Home

TROUBLESHOOTING NUCLEAR INSTRUMENTS

Contents

1. TABLE 6 3 Failures in the circuit of Fig 6 2 due to resistors R3 open circuited E2 VE E2 IE 0 The case of RB short circuited can be investigated only by direct RB measurements If the above described tests visual inspection transistor fault diagnosis and resistor short circuit open circuit test do not show anything abnormal measure the resistor values after removing the transistor 109 Chapter 6 6 Consider now the circuit of Fig 6 3 which shows a transistor T3 in the common base configuration If you suspect that there is something wrong in this c rcuit and that it may be responsible for the wrong behaviour of the network to which it is connected check first the voltage between B and ground If such a voltage substantially differs from the nominal value EIR2 E2R1 Rl R2 it has to be concluded that the circuit is faulty The fault may actually depend on C behaving as a short circuit because of an irreversible damage occurred to it on Fig 6 3 Transistor stage with transistor T2 or on the voltage ac coupling divider Rl R2 If you conclude that C is short circuited disconnect C on one side and measure VB again to have experimental evidence that your hypothesis is correct There may be some situations in which C is not a true short circuit but presents
2. 90 004 Sq 1 DIVA 1H Chapter 5 ON 36 1 300007 15v pase beni 13 TR 205 ameo suas srivaam Er Caves 40 3018 NLOS NO 1 S 1V210w Dy 9 590151930 209 NV SILWIIGN FS 009 N JUV 630010 TV 03108 ATT SUV SOLID Tw 0340N 5911 E L 1 Swoisisry YW OLLON 7 2070043006 NO 5311 AM ON RIV J3l l ISILON ndi N23 335 Conwy O 4a2 25 03 A33 3 an 3 oost vo x HO o m ET lt emus nt TE I anvisa ti CK 7 au ite ATIC t e Senn aste T amp aviv tee Kot yu Low Voltage Power Supply of a MCA 4 5 Fig 91 Chapter 5 14 variac ac line line input Fig 5 5 Using a variac to identify a fault The arrangement as shown in Fig 5 5 can be used also for testing in the case when the fuse F101 is blown immediately when the instrument is switched on This indicates that there is a short circuit somewhere in the power supply Before you start to look into the circuit in detail remove the whole load take out all boards disconnect the display unit Slowly increase the output voltage of the variac and observe the current with an ammeter see Fig 5 5 When the ammeter indicates roughly 60 80 of the nominal fuse current stop increasing the voltage Now measure the voltage at the ouput of th
3. 00000 o o 00000000 00000000 00000000 00000000 Fig 9 30 Matrix representation Fig 9 31 Video signal drawing the first line of E Having the character code at outputs Al to A6 of the ROM 108 the output corresponding to the vertical line pattern of the required character appears at Bl to B8 To reproduce E for example the thicker points should be brightened When the beam runs from bottom to top of the screen and arrives at the letter E the pattern 1111111 should appear at the ROM output Then two 4 bit 200 29 Chapter 9 shift registers 106 and 107 are loaded with Bl to B8 data The pattern is then pushed out in the serial form corresponding to the first vertical line of the loaded character TP30 and the command shown in Fig 9 31 is delivered at the CVID line CHAR LATCH E 3 STATE LATCH CHAR GATE CHART GEN SHIRT REG Fig 9 32 Character display block diagram LOCAL DATABUs D0 AD7 CVID DTCK After this the second character is pushed down from A91 to A90 to draw the pattern of the upper character line Only the first line of both characters was used Therefore we don t need to change them yet but we have to keep them The lower character stored in A90 is returned to A91 to be used again in the next vertical line After using all eight lines of both characters A91 and A90 are reloaded However to write the second vertical line of the same character t
4. ATN ATTENTION MTA MY TALK ADORE SS Outputs T TALK ENABLE TEO TALK ENABLE DELAY 4122 4 My Tab Adorees Laich FROM INTERNAL CLOCK FROM RESET LOGIC BUS GENERATED BUS GENERATED ACTIVE WHEN READY TO RECEIVE THE NEXT BYTE FROM THE BUS ACTIVE AFTER DECOO D BYTE HAS BEEN ACCEPTED BY THE MODULE ACTIVE FOR ONE CL OCK PERIOD DURING STABLE AND VALIO DATA STROBES ALL MODULE DECODERS AND LATCHES FROM INTERNA CLOCK FROM RESET LOGIC BUS GENERATED BUS GENERATED FROM TALK DELAY GENERATOR FROM TALK DELAY GENERATOR FROM OUTPUT DATA SEQUENCER GENERATED TO SYNCHRONIZE INTERNAL CIRCUITS ON EACH OUTPUT BYTE INACTIVE DURING THE PERIOO WHEN STATE AND BYTE CHANGES ARE OCCUR RING GOES INACTIVE ON DAC ACTIVE ON THE RISING EOGE OF NEXT CK AFTER BYC GOES INACTIVE GENERATES DATA VALID TO THE BUS GOES ACTIVE AFTER A DELAY TIME ALLOWING DATA TO SETTLE AND RFO INACTIVE AFTER DAC ACTIVE INDICATED BYTE RECEIVED ON THE BUS GENERATED BY DAC ANO VALID TO THE ENO OF BYC FORCED BY TE ORRDY TO PREVENT BYC SENT TO COUNTER CLOCK BYTES FROM THE COUNTERS IN S3 DATA CHANGES TO NEXT 158 ON THE FALLING EDGE OF ACL FROM INTERNAL CLOCK BUS GENERATED FROM MY TALK ADORESS LATCH ACTIVE FOR TALK STATE SYNOHRONUES BUS TO INTERNAL CLOCK FOR CORRECT TENG Opus SRO SERVICE REQUEST SPR SERIAL POLL RESPONSE 8 Outp tt Data Sequencer and Gating routs Te TALK ENABLE Tet TAKE IT SPR SERIAL POLL
5. h 250 nsec I t pod Cas ae DATAV I t 1 t RORAM 83 nsec DMA Read Timing 1 1 1 pod d H D t 1 I i I 1 i I 180 ns E NES L 1 1 k if 1 il I 4 t t m i I ey oe EIN GEN OTHAR Was Cas OaTAV WTOTa wT 193 la 2 sig Dats In Valid 1160 Data Out 166 ns DMA Read Modify Write Timing 9 22 DATA aus Fig Chapter 9 22 9 10 CURSOR CONTROL The aim of this circuit given in sheet 3 CPU board is to control the cursor position Its implementation into the board can be seen from Fig 9 23 MOTOR SCR CONTROLLER Y D0 D7 Fig 9 23 Cursor controller connections The command in the form of a binary number to move the cursor is given to the CPU through the three state latch A681 74LS373 The latch receives data from two bidirectional four bit counters A82 and A83 74LS191 which are periodically scanned for the data Counters count pulses from the VFC Voltage to Frequency Converter A84 4151 VFC driving voltage is provided by a DC motor serving as a generator when rotated Negative or positive voltage applied to the operational amplifier connected as a rectifier causes the generation of the clock signal at the output of VFC The same frequency res
6. F C F 29 XXXXX SKILL elect one h 11 Chapter 3 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX S General instructions on soldering Soldering and desoldering is one of the main tasks in ronic troubleshooting work To solve these tasks properly as to consider several points l The physical dimensions of the soldering point The range is from tiny hybrid circuits watches double or Multi layer boards e g pocket calculator up to big area soldering e g for shield grounding 2 Material on which soldering must be done Normally there will be a printed circuit board covered with special protection varnish or tin silver gold etc but also on stand offs leads plates cables etc Let us assume all material is tin solderable nevertheless there are big differences e g for iron and gold In addition to the different heat transfer also different surface conditions have to be considered IT IS ESSENTIAL THAT FOR THE SOLDERING PERIOD THE TWO MATERIALS REMAIN CLEAN NO ORGANIC MATERIAL OR CORROSION 3 Material used as solder The material normally called tin is in reality an alloy which is mostly composed of other elements like Pb Cd Ag Bi Cu and Sb TABLE 3 1 Some common types of solder and their composition Specifications Standard Melting A QQ S 571E G DIN1707 Alloy Point C B BS 219 Used for TLC 145 B T G L SnPbCdl8 solder of galv gol
7. 40709 KMN ase Bante fast 8 azaaqdey 991 cna ame tanara oe RASTA GI G9 vr Gla na 425 ree sue ua C leu rt 0 eA Gp 44 O occer eno lt e CX Axioo enata Jia 9 cae teat l N I 445 sr se a a lt ae atts JEE e 191 Fut wells 145 Gare 8 21e3deu5 891 ensa or ge 2201 srog 28 tev and NAT Zee ice DEALS TIE SEET CORNET ON Karts Fa NAAT SOV BATS PER 13 AF CAnEDAMAT 3 WEE 43 Lown aT e 545 2 4 BO OCA ES CONN d C 07 ON SAE Aur 4 E COOLMMATES BL 13 Foot CL ecard Comm Cac aw PC ALA A af OG a C st sre 6 C561 he ste ars c x te pana are go gt gom srs Ye E 7 1e3 gt 2t 4 4 e Gay gt 4 6 540 4 ca x a x x T gt lt af E 2 mari C car WOES L et a 41 OXA Ca ML re an X4 c PP COE lt gt xy c Coti x amp 4 THEEL ALE 9 way TUS SCHEMATA 4 9 AE wS rot a r vww Mecrt40 MSS rors Ali 700K y 4 2 v
8. 5 4 1 Circuit Description The power transformer provides four separate low voltage ac sources These sources are full wave rectified capacitor filtered and regulated by electronic series regulator circuits which have the capability of regulation and current limitation with foldback characteristics Each supply voltage has its own reference source and the possibility to adjust the output voltage by a potentiometer All four supplies use the same active components however the voltage dividers are tuned to the requirements of the output voltage Two different preregulators are used one consists of the voltage doubler 01 D2 Cl C2 4 zener diode D4 for the 12V and 24V supply The second uses a 10V zener diode for 12V and 24V supply The reference voltages of 6 95V are derived from a reference diode Ul U3 U5 U7 The regulators are of the type LASI1000 or equivalent As a pass transistor a mpn Darlington transistor is used type TIP100 or equivalent A reverse current protection is also built in by the reversed biased diode from the type 1N5819 or equivalent Following the above observations it should be easy to troubleshoot the instrument Nevertheless the following additional comments might be useful There are two shock hazard locations to watch for the wiring side of the input line cord connector block and the two thermal switches Sl for thermal cutout S2 for thermal warning mounted against
9. and BA10 demultiplexed in 3 to 8 demultiplexer A78 are used to produce the strobe signals RO R2 and R4 Multiplexer A78 is enabled by OUT output request generated within the CPU board OUT can be checked at TP23 By these signals applied to four 8 bit latches A101 A103 A84 and A102 four bytes of the information can be stored R4 is used to enter the data into A60 the dual flip flop Through some additional processing in two multiplexers A83 and A65 the complete display status is created From the latched data you can learn what is the memory range MO Ml M2 or the display mode or similar 199 Chapter 9 28 ADDRESS DAA 9 INTERNAL BUS pg dott YAT UPPER Tao on CORP MESo AN OG VEN METE 19 404 am w our m amp T ADR 6039 1 Fig 9 29 Status register 9 11 5 Character Display and Video Mixer Characters are displayed in the dot matrix form 5 x 7 in our case The character cell size is bigger 8 x 10 dots Fig 9 30 Characters to be displayed are accepted from the local data bus Fig 9 32 during the direct memory access DMA cycle and loaded into the 8 bit character latch A91 sheet 4 followed by another 8 bit latch In this way a two byte fast memory is created When the second character is accepted immediately after the first one the first character is transferred into latch A90 Fig 9 32 00000000 Qooooooo Qooooooo V Qooooooo
10. 5 l OL 39VL IOA LNIWLSOLGY AH c TISNNVHO YVaTONN AIddNS AIddNS N3MOd H85VL OA MOT SNIVW 35VL IOA HOIH Chapter 11 QIONLNOO TWONWH H3MOd SNIVW Alddans HOLOW LIQn2NIO MHOLOW 5SNIdd3IS X 21901 HOLOH ps bd IOULNOD 4d4O NO X HOLOW ONIddaLs X LNSWLS PGV TONLNOD daads cj x x T L I nT AONANO AYA S ONIddaLs ALISNSG NOILVWWOSNI SHOSNSS NOILISOd S5NYH MOGNIM ROWING 727 3 77 Landi bd LHOIGH ASIANA crm e 3012414 AdOLOSI TENDIS YOLIALIG NOILV TIILNIOS VIIN PES 7 ALWu ONILNNOD YOLOALAG SOS SS 4 J YVLIOA HOIH HOLOd3ILdd Block schematic of a typical scanner 11 16 Fig 270 31 Chapter 11 The regulated voltage supplies of the X Y motors are rather simple their rated output is between 150 300 VA They are designed to deliver ample power to start moving the detector by the stepping motors The speed regulation is accomplished by changing the frequency of the steps The rotation direction is changed by altering the phase relations in the control coils of the motors The high power semi conductors might fail more often if the ventillation of the heatsinks are obstructed
11. Porre Alarm circuits Input from o if ferent Sensors Fig 10 13 Closed loop stepper motor driver with position encoder There are two possible faults The first is the driving circuit as described before The second is the position encoder 236 27 Chapter 10 which indicates the momentary position of your driven system It strongly depends on the encoder which kinds of signal are fed back to your controlling device If you find out during troubleshooting that the driving circuit works correctly but the position is incorrect you have to check the feedback loop Depending on the position of the encoder use check if the output signals are correct 10 8 CONCLUSION Dealing with interfaces especially if they don t work can be a tough job Nevertheless you have to do it a few additional tips for troubleshooting are listed below l Never start your job before you have read the operating manuals a lot of problems result from a wrong setup and operation 2 Before you start troubleshooting on boards study the circuit diagrams if they confuse you try to draw functional block diagrams for it makes your job easier 3 Write down everything you are doing maybe the next day you won t remember what you did 4 Follow the signals from the destination to the source 5 Make timing diagrams to learn how signals are related together 6 If possible try to implement your own simple test software
12. 4 7 mons UAMESS OTHERWISE 1 TNE ARE 004 WAY TIED ON r BCHEMMT C L AU crt al 1C 03B8 AAR ae 1 4 OUTPUT VOLTAGE 550 m i 3 Alu RESSIORS GAL 1 OMAK Ub TAX NV OUTPUT METER PION 1 TOR INOCATES COAX PERINAT ION 4 wbicATES w RE POINT On PC para dust bon 6 P SYMBOL INDICATES ANEBC L 1 0 1 3 lt va ANSSE t PASSE RIK o i amp 2 7 OvVERVO TAGE oerteroe STEED V 2 EFFECTIVE g l OOo OVER VOLTAGE i DETECTOR 09 Circuit diagram of Canberra Model 3102 4 Chapter 5 Measure with the digital voltmeter the 9V reference Adjustment be done by changing the potentiometer R172 IC 101 pin 1 Next check if the setting circuitry works properly This is done by varying the front panel potentiometer or by changing the voltage selector switch at the front panel while monitoring the voltage at the output of IC 103a pin 1 Now check with the oscilloscope to see if the oscillator is working the signal at the output should have a trapezoidal signal with an amplitude of about OV to 11V and a frequency of about 20kHz If not measure the inputs with an oscilloscope and compare them with the output C108 should be charged and discharged amplitude about 6V to 11V Due to the not very sharp signals at the outputs of IC A5 pin 6 and 8 a triangular signal sitting on
13. a set of screwdrivers Allen keys plyers flat keys a pulse generator s PG with which nuclear pulses can be simulated both for analog pulses for digital pulses and a radioactive test source with known activity preferably the same as used during acceptance testing In order to do troubleshooting one should know 1 the usual composition of a Nal detection system and the functions as given in Fig 4 1 2 the forms of the signals at the output of the PMT the preamplifier amplifier and single channel analyzer 3 why one does not observe a signal at the input of a charge sensitive amplifier 4 that the rise time of the pulse at the output of the PMT depends on the half life of the scintillation process the detector and 5 that the pulse heights and shapes at the output of the pulse amplifier are so chosen as to fit best to the SCA or MCA and to guarantee optimum spectrum resolution Each of the following paragraphs gives a possible indication of failures as may be given by instrument users operators and a list of possible origins or reasons for these failures and when not obvious actions to be taken There may be among the operators very unexperienced ones This may lead to some reasons which seem ridiculous nevertheless they are based on experience the field 4 3 THE INSTRUMENT DOES NOT WORK To be checked Is Is the nstrument switched on 2 Is there power on the AC outlet 3 Are
14. oues If special heads other than e g tne bit in a hexagon socket 100 mm long 1 4 inch socket Example of different sizes of Pozidrive bits No 855 Setew rivers for Pozidriv Supadriv slots C form Extra hard quality HRC 64 65 Specidlly intended for tightening sheet metal screws lt Orig No 855 1H 1 5014 5015 Ref 5014 0052 0102 0201 0250 Pozidriv slots No 0 2 25 2 50 TORAN SSIS Length mm 25 25 25 50 Std pack 10 10 10 10 Price each SEK 525 525 525 875 Orig No 855 1H Ref u 5014 0284 0300 0409 Pozidriv slots No 3 25 3 32 4 Length mm 25 32 32 Std pack 10 10 10 Price each SEK 525 12 00 14 50 Fitting in universal holders 851 1 ea 655 1 n O ax sez different types of bits 28 Pozidrive are needed use different bits in a holder a spring collar or a magnet BC C F ABC F BC then holds C F 3 1 12 Allen Keys f e 3 1 13 Pliers sic AB length keys are removeable from the holder metric set 1 5 6mm hex inch set 1 16 1 4 hex for multiturn dials of precision pots additional special sizes should be ordered flat nose plier length 170 mm snipe nose plier length 120 mm half round nose plier 140 mm combination plier length 160 mm water pump plier length 130 170 mm wire strip plier length 130 mm Chapter 3 BC F BC F C
15. symbols must be according to local standards It is a good practice to mark points where stages can be isolated from each other with indication of possible test signals and expected correct outputs 64 45 Chapter 3 In the case of missing drawings and documentation the functional diagram preparation is recommended as an efficient aid in repair work vs the traditional draftsman approach XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 65 Chapter 4 TROUBLESHOOTING IN SYSTEMS Chapter TROUBLESHOOTING IN SYSTEMS 4 1 INTRODUCTION A Nal detector is used in many fields of application of nuclear techniques e g in nuclear medicine radioimmunoassay agronomy radiation protection and uranium prospection Therefore a Nal detector system was chosen as example of troubleshooting in a detection system Such a system consists of a detector usually surrounded by a radiation absorbing shield and a collimator a preamplifier an amplifier a single channel analyzer SCA a scaler timer or ratemeter instead of the last three a multichannel analyzer MCA Furthermore the system contains a high voltage supply HV and several low voltage DC supplies LV The units composing the system and their functions are given in Fig 4 1 For other detectors a similar set of electronic units is used with characteristics adapted to the particular detector In the following text examples
16. 0 Ty EU Lr Ud w 101 s Cory w0 _ wf p Y Q NE 2 lt P ese zi 3 t3 te tele AY we HAD I ORY ee oN I ALL eN y Le 4919624 25 VO 3 t s asy 4414 MM v Arhat 452 Or Y e Bas 2 J ok Man O 5 H4 cr p mE s E TII ER op ul Da 1 lt bod 3 6 lt nj 950 j RO is o29 xa T a S psa e port of Interface circuit diagram for the RS 232 a MCA 35 10 4 Fig 219 Chapter 10 10 ATTENTION Don t connect Pin 20 it can damage your driver in the PC Next you have to provide the options in your computer to the setup chosen on the serial interface in the MCA You will find a detailed description the setup of the interface board the Operators Manual of the MCA Take care you cannot exceed a baudrate higher than 4800 bps because no handshake is supported Some hints if you run into trouble when installing your interface are presented in Table 10 1 TABLE 10 1 Partial list of problems with an RS 232 interface Symptom Equipment Cause Remedy No data is being Terminal or Check to be sure that power is on displayed or printer Ensure that device is in on line printed mode RS 232 requirements may not be satisfied Polarity of signals could be impro perly set Both dev
17. Below you will find the pin assignment and description of Signals seen from the printer side in our case an EPSON Signal Return Pin No Pin No Signal Direction Description 1 19 STROBE In Used to strobe Latch data in A pulse gt 0 5 us at receiving terminal is required 2 9 20 27 DATA 1 8 In Eight TTL compatible data lines Each has its own signal ground return for use with twisted pair cables 10 28 ACKNLG Out Output pulsed low for approx 12 us and indi cates that data has been received and that the printer is ready to accept more data 11 29 BUSY Out HIGH indicates that the printer cannot receive data The signal becomes HIGH in the following cases during data entry during printing operation in OFF LINE state during printer error status 12 30 PE Out A HIGH signals that the printer is out of paper 13 SLCT OUT Out A HIGH signals that the printer is in the selected state in most printers pulled up to 5V through 3k3 14 AUTO FEED XT Out When this input is low the paper is automatical ly fed one line after printing 15 NC Not used 16 In Logic ground level 222 13 Chapter 10 17 GND Out Printer chassis ground Normally isolated from logic ground 18 NC Not used 19 30 GND In Twisted pair return signal ground level 31 INIT In When this input is LOW the printer controller is reset to its initial state and the print buffer is
18. Chapter 9 14 counting system is additionally preloaded with 1 2 3 up to 18 The resulting binary number would thus be too big by 1 2 3 To get the correct value this number is subtracted in the adders A63 A64 A65 and A67 Subtraction is implemented by the addition of the two s complement Lines QLO to QL12 with the signals representing the result of the conversion have to be connected to the address data bus BADO BADL BAD2 BAD4 BAD6 BAD7 AB A9 A10 All A12 The connection is done through three state buffers A33 and 44 are used between 9 4 CPU BOARD 9 4 1 Processor Description The heart of the CPU board is the INTEL 8085 microprocessor with the pin assignment shown in Fig 9 15 Because of the shared address and data pins an additional latch must be added externally to create the normal 16 bit address and 8 bit data bus from the microprocessor ADU AD7 and A8 15 lines TABLE 9 3 Status signals STATUS SIGNALS S0 S1 10 of Machine Cycle 1 0 Op Code Fetch OF 0 1 0 Memory Read MR 1 0 0 Memory Write MW 0 1 1 1 0 Read IOR 1 0 1 1 0 Write IOW 1 1 Interrupt Acknowledge INA _ 0 1 0 Bus Idle X1 vec 2 HOLD RESET OUT HLDA 500 CLK IOUT SIO RESET IN TRAP READY RST 75 IO M RST65 Sy RST55 RO INTR wA INTA ALE Do So A15 AD2 14 A03 A13 AD4 12 ADs AW AD6 A10 A07 Ag vss AS Fig 9 15 8085 microprocessor 186 15 Chapter 9 ALE Add
19. Fig 12 5 The nitrogen transfer device The detector cap is connected to the dipstick with a flange see Fig 12 6 An O ring takes care of vacuum tightness of the joint Be careful not to pour liquid nitrogen on the flange The cooling will make the rubbery material of the O ring brittle and a vacuum leak will develop Some manufacturers use metal rings they are safe as far as the cooling is concerned but are difficult to replace 286 9 Chapter 12 By mishandling liquid nitrogen can be poured on the flange While this is bad it is not necessarily a catastrophy Tighten the screws holding the bottom and top flange together you might be lucky and the O ring can be squeezed enough to still hold the vacuum It is a recommended policy to keep the detector in liquid nitrogen all the time The shortage of liquid nitrogen might force you to let the detector warm up If this happens let it warm up all the way i e let it spend a day or two at room temperature before it is cooled again Deirin Detector Lexan Copper Aluminium Fig 12 6 The inner life of a semiconductor detector Note the flange with an O ring High resolution detectors are sensitive to mechanical shocks Be very careful when moving them A special feature of these detectors is microfony Mechanical vibrations or accustic signals will be transferred to the detector and undesirable noise will be produced Different precau
20. Por gi 27 Chapter 6 Check whether the voltages at points A B C and D are close to the values specified before VB R7 R16 V1 R6V1 R6 R7 R16 VC VB lt ranging between 0 1 and 1V VA VC R4 x 2Vl note that R3 R6 R6 R7 R16 There are three possible sources of trouble l The channel of JFET 01 is OPEN 2 The transistor Q2 has got either base emitter junction OPEN or emitter collector path OPEN 3 The current source Q5 does not provide current You can easily distinguish situation 1 from 2 and 3 by measuring the voltage at point A If such a voltage is equal to V1 then JFET Ql has an open channel for it drives current although the positive voltage at Q4 emitter through the 100 MQ resistor forces a forward bias of Ql gate to source junction If the FET is suspected remove it from the circuit and check it with the circuit of Fig 6 21 a and b a 0 9 logs 0 9 Joss 6V Fig 6 2la Measuring IDSS Fig 6 2lb A circuit to measure of a JFET the transductance If the charge sensitive loop has correct dc conditions troubleshooting can continue by checking the output amplifier However if these voltages are far from the specified values and as frequently happens in a damaged charge sensitive preamplifier VD is some volts positive the following failures may have occurred 131 Chapter 6 28 No drain current is measured in th
21. Some Prom programmers on the Bi polar devices and PALs But 56 normally PAL circuits copying is possible spare PAL circuits have to be ordered from the manufacturer device RS 232 Centronics 3 adaptors for copying different types of E Proms 2 adaptors mainly used for multiple copying of E Proms gang programming are also able to program are protected and therefore 37 Chapter 3 The Prom Programmer described requires for E Proms a personality module for the individual Prom families to be programmed Especially with new devices it takes some time until such cards become available from the manufacturer and sometimes even a modification to the basic instrument is necessary to provide the required features New Prom Programmers which are now available allow programming of the individual parameters for burning a device into their memory and are therefore more flexible Personality cards for these instruments are not necessary 57 Chapter 3 38 3 4 RECOMMENDED ELECTRONIC COMPONENTS Below is a list of spare parts and electronic components that are considered to represent an optimal store for a medium large electronics service laboratory The last column in the catalogue number refers to a large mail house in the FRG Fa Buerklin P O Box 200440 8000 Munich FRG The value of these components is about US 4 000 By adjusting the number of ordered components a less or more expensive st
22. 17 and CHLD A26 During data handling the be set See Table 9 DATA Deum 4 corresponding schematics are shown in AoORESS Mux A4 496 99 oa ra Mux 3 ovr proper for the required sheet 7 DMA Bud SiG ALS DATA cre AMT AOQNELZYDATR BW Fig 9 34 DMA TABLE 9 4 DMA addresses A3 A5 D2 LO Ed LO L1 L2 O n Li L2 L3 a L2 L3 L4 O E L3 L4 15 lt LU 15 16 5 16 L7 L5 16 17 A6 Lu L5 L7 A7 L3 L4 L5 L6 L7 L8 A8 L4 L5 L6 L7 A9 L5 L7 L8 43 48 err A10 All L6 L7 L7 L8 18 0 0 0 0 0 0 0 0 0 0 OMA CONTROL BURST q INTERFACE A96 235 437 439 ane ont w Cu 98 30 12 A13 18 BO 0 BO 0 BO 0 BO 0 BO 0 BO 0 BO 0 1 2 byte Chapter 9 Check TP25 for some activity at TP20 memory A91 A90 pin 13 are used RAM and ROM addresses have to combinations The 1 B1 81 B1 Bi Bl B MERO Y C Comoe 53 004 srrar pat cona CwAt 15 203 Chapter 9 32 9 12 MISCELLANEOUS BOARD The miscellaneous board is responsible for various activities such as communication with the keyboard and communication with external units through the serial interface RS 232 or TTY However the most important task is the mathematical operation during the pulse height analysis PHA As
23. E Ra APPLY TO fy THE ROUBLESHOOTING PRaCEDUCE BASED UPON gesse R NOMINAL VALUE DETERMINED BY VOLTAGE DIVIDER OMIM VACU DETE RMIED Y VOUTALE Di Rs a 2 CLOSE TO THEIL NOMINAL VALUES YES TEST NEW SPECIMEN OF THE SAME TYPE OR or A RECOMMENDED FOR PEACE NOLL THE CifCo rr WIR TNE NEW Fig 6 9 Flowchart for troubleshooting a basic transistor 118 stage 15 Chapter 6 Troubleshooting considerations similar to the previous ones can be applied to instruments or parts of them based upon operational amplifiers An instrument may be designed to use several operational amplifiers The search for a fault in the instrument requires a fault analysis for the individual operational amplifier circuits which can be introduced with a quite general approach by discussing the connections as shown in Fig 6 10 Fig 6 10 Basic operational amplifier configuration Suppose that the output voltage Vo which should be close to zero if this circuit is intended to a linear amplifier is found instead to be close to the positive saturation voltage ll to 14V depending on the type of operational amplifier employed for 15V bias Assume also that visual inspection has been accurately carried out on the circuit and that nothing has come to your attention Follow the instructions suggested in the flow chart presented
24. VERTICAL AXIS GATE OUTPUT A and B 50 Chl Ch2 used for vertical analysis Y Ch3 Ch used for X and ext trigger time reference HORIZONTAL AXIS Ch 2 modes mode is switch selectable HORIZ DISPLAY SWEEP modes A ALT A INT B B DLY D DUAL X Y HOLDOFF delay method continuous delay trigger delay delay time 0 2 to 10 times the sweep time from 200ns to 0 58 continuous ly adjustable B modes STARTS AFTER DELAY TRIGGERABLE AFTER DELAY BC F 31 Chapter 3 3 3 8a Double Pulse Generator The simultaneous positive and negative outputs deliver 2 watts into 50 ohms Pulse amplitude width delay and repetition rate are continuously variable Other capabilities include single or double pulse operation external triggering synchronous or asynchronous gating reference trigger outputs sine wave triggering and manual single pulse operation Specifications repetition rate 10 Hz 10 MHz external trigger 0 25V 20nsec min 50 Hz 10 MHz sin lVrms manual cycle synchronous asynchronous gating possibilities advanced trigger 1 7 V min 1508 reference trigger 2 V min 15ns pulse mode single one output pulse at the end of the delay period double two identical pulses per cycle first after the reference trigger second after the selected delay pulse delay 40 ns 10 ms pulse width 40 ns 10 ms pulse height 0 5 10V 50 ABC F 51 Chapter 3
25. values from 0 to 99 This information is loaded in the down counters 42 units 43 tens The power r is used to control the output of the six decade counter A51 if r 0 the output has the same number of pulses as the input in general the output corresponds to a division by 10 r Pulses for the down counters come from the output of the decade divider A51 through gate A4ld This gate is enabled by the output of A4lb while the preset count is not reached When the preset value is reached the output of 41 becomes 1 and through A28d and A6 stops the counting process Capacitor C3 filters out eventual negative spikes that may trigger the following circuits Gate 284 may be closed by A31 allowing the counter to be open indefinitely A31 an 8 input NOR gate closes A28d if the preset value to the down counters is zero 8 4 TROUBLSHOOTING EXAMPLE LCD DISPLAY OF DUAL COUNTER TIMER CANBERRA MODEL 2071 Here we just refer to the display section of this instrument the block diagram channel A of which is presented in Fig 8 4 The 6 digit display can either show the contents of decades D5 to DO or of decades D7 to D2 according to whether the contents of the most significant decades D7 D6 is zero or non zero this is implemented by the scaling block The contents of the various decades is transferred through a bus to the latch decoder ICs associated with each digit the latches are successively enabled by the stro
26. 1 333de Chapter 8 SCALERS TIMERS RATEMETERS l Chapter 8 8 SCALERS TIMERS RATEMETERS 8 1 TYPICAL STRUCTURES OF SCALERS TIMERS AND RATEMETERS To be able to service and repair scalers timers and digital ratemeters it is essential to correctly identify the different blocks in which the instrument may be logically divided and to understand their interactions To help in this procedure a short description of typical structures is given below detailed description of examples of commercially available instruments completes this chapter 8 1 1 Introduction The general block diagram of a typical counter with preset count capabilities is shown in Fig 8 1 OUNTING STAGES PRESET CIRCUITRY Fig 8 1 Block diagram of a typical counter The signal to be counted can in general be easily followed through its path in the counter and defective ICs can be located without too much difficulty Circuitry associated with preset count and gating is generally more difficult to troubleshoot because of interactions among several control signals As an example of faults which are hard to find we may quote the spurious counts due to bad filtering by a defective capacitor 8 1 2 Input circuits Most input circuits accept NIM logic signals positive and or negative Some counters have discriminator type inputs allowing analog signals of small amplitude to be counted One must check whether the input circuit passes the sign
27. 158 5 Chapter 8 The functioning of the counting circuits can be easily checked if they consist of individually accessible decades binary counters When one is dealing with LSI counters where the output lines are time shared by several decades the functioning of each decade may be observed by externally triggering a scope with the scanning clock signal Preset count circuitry may be checked starting from the storage of preset information followed by observation of the count down or by examination of the comparator circuits that test when preset count is reached according to the approach used in the instrument to implement the preset function 8 3 TROUBLESHOOTING EXAMPLE TIMER SCALER CANBERRA MODEL 2070 block diagram of this timer counter is shown in Fig 8 3 some semiconductor components not all are indicated to help in identifying the blocks PRESET COUNTER A42 43 A51 A31 A41 A6C GATE CONTROL VENT TIMEMUX A45 46 A52 D20 D21 TIME BASE TIME GATE A33 36 A15C A46b SINGLE RECYCLE A15a A14 A24 A41 Fig 8 3 Block diagram of Canberra 2070 timer counter 8 3 1 Input and Event Gate The dc voltage at the input is approximately OV for it is imposed by Q9 whose base is at about 0 7V as set by the diode connected transistor Q6 NIM positive logic pulses actually any positive pulse larger than about 0 7V saturate Q10 and cut off Q9 NIM negative pu
28. 23 Chapter 10 lines are unidirectional and form a subset of the system The PIA thus appears as a number of specific memory or I O addresses which may be selected by appropriate software instructions The PIA also utilizes the CPU control bus when for example a RD and WR signal is used to determine the direction of the data flow from to the PIA In addition bidirectional buffers are used to interface the peripheral lines to the PIA These buffers are generally TTL compatible and provide limited current drive capability typically in the order of ImA As a typical example for a PIA we will take the 8255 which is also called programmable peripheral interface PPI see Fig 10 10 Fig 10 10 Pin out of 8255 programmable peripheral interface As an example of the use of PIA devices we will consider the operation of a keyboard decoding arrangement see Fig 10 11 On most computers the keyboard consists of a matrix of 60 or more switches with the possible addition of further switches reserved for specific functions The key matrix is arranged in eight columns and sixteen rows Ports A and B are configured as inputs while port C is configured as an output Note that only half of port C 15 utilized and that the four output lines are taken to a four to sixteen line decoder This device effectively scans the keyboard rows addressing each in turn as the b nary count on port C is cycled through its sixteen states under software control
29. 40 ABC ABC ABC BC ABC ABC BC BC ABC BC BC BC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC or mo rn rn rz m m rm r rr 5 x 21 Chapter 3 Modular switchable probe with xl and x10 attenuation AH 10 1 Bandwidth DC 250 MHZ rise time 1 4 nsec input resistance 10 Mohm AH 1 1 Bandwidth DC 10 MHZ rise time 35 nsec input resistance 1 Mohm Modular probes allow easy repair of broken parts any module can be simply replaced ABC F 3 2 7 Oscilloscope Current Probe Sensitivity 1mV mA Accuracy 3 Bandwidth lkHz to 40 MHz rise time 8 nsec I max dc 0 5A I max ac 15A 41 Chapter 3 SIDS 3 2 10 Shielded Black Box For compact packaging of matching networks Features shielded housing of die cast aluminum Includes cover and four self trapping screws BC 3 2 11 BNC 50 Ohm Terminator Plu 1 0 5 watts 100 C max gold plated center contact BC F 3 2 12 BNC 50 Ohm Attenuator Impedance 50 Ohm f range DC 1 GHz Accuracy 0 2 dB Max Power 1 Watt 42 23 Chapter 3 3 3 INSTRUMENTS Selection of instruments for troubleshooting and development may be troublesome because nowadays a large amount of different types even for similar purposes are available on the market Even experts are only familiar with a few types of instruments and these are mostly instruments they are dealing
30. In industry radiation and associated nuclear instruments are applied in products and in process control As a rule nuclear instruments are rather sophisticated and delicate instruments If they develop faults as any instruments sooner or later do they are not easy to repair Considerable specialized knowledge extensive experience and suitable equipment is needed for their repair and servicing For a price the manufacturers of nuclear instruments offer the required service for their instruments If sufficient funds are available a service contract can be established and the manufacturer his service laboratory will take care of the installed instrumentation This is sound practice for a laboratory in an advanced country where the manufacturer s service person is available on call and where the rather stiff prices of the service contracts can be accommodated in the laboratory budget In developing countries both commodities available service and sufficient hard currency are an exception rather than a rule The management of developing laboratories must find an alternative solution Creating a maintenance and service laboratory in an institution in a developing country is not easy Following reasonable advice like some given in the present publication can help in the selection of suitable testing instruments tools and components However the training of the staff who must have all the required skills knowledge and experience
31. gt last byte of a datablock EOI 1 ATN 1 gt parallel poll 9 IFC Interface Clear Resets the whole system 10 SRQ Service Request has same priority for all instruments in a system Is active whenever an instrument requests a service Control ler will interrupt and start with a serial poll to deter mine and satisfy the reques tor 11 ATN Attention 0 Data is transmitted ATN 1 Commands transmitted 6 DAV Data Valid indicates the data on the bus is valid 7 NRFD Not Ready For Data is sent from the instru ments to indicate that they are not ready to accept data 226 17 Chapter 10 8 NDAC No Data Accepted is sent from the instruments that valid data on the data bus have not been overtaken yet 12 SHIELD 18 23 GND 24 LOGIC GND ids j B fret omne f tn DAV VALID VALID VALID NOT VALIO SOME ALL INSTRUMENTS READY m PP altel fi j NMO INSTRUMENT R NRFD I SoME ALL FPMJMETROQM amp HTZI re DATA OVER NO INSRUMENT A f TOOK DATA OVER i NDAC 1 nen Fig 10 7 Timing diagram for handshake As example we will take the Canberra counter timer 2071 with the installed GPIB option see Fig 10 8 Before you can operate the scaler in a GPIB system you have to configure the interface through eight DIP switches The first five switches from the top are used to set the units GPIB address The address i
32. 1 Shen 200 3k 86 200 MO AUTO ON 19 A 004 1m 20m 200 2000 0 asoy PEAK MAK Features edBm Relative Functions eMin Max Reading Hold Da Safety Input Jacks 4 Digit LCD Display ate eFast Autoranging e10A Capability eBench or Portable 100kHz Specified AC Bandwidth Digital Calibration 100 Point Data Logger 10nV 10m2 10nA Sensitivity 0 03 Basic Accuracy eTRMS Options Model 1758 Rechargeable Battery Pack Model 1753 IEEE 488 Interface A remarkable feature of the instrument shown above is the Data Logger This is specially suitable for longterm measurements as for example the line fluctuations instabilities superimposed slow variations on dc lines 100 data Hi and Lo can be stored in 6 different speeds from 3 reading sec to 1 reading h Options battery pack supply for 6h IEEE 488 interface for remote control BC F 47 Chapter 3 28 3 3 3 Capacity and Inductivity Meter digital direct reading 3 1 2 digits 48 The instrument is battery powered accuracy lt 0 54 lead compensation possible Capacity 1 10 100 l 10 100 pF pF pF uF uF uF 20 100 20 200 Inductivity 1 10 100 1 10 9V uH uH uH mH mH 20 200 nF nF nF uF uF uF mH mH mH ABC 29 Chapter 3 3 3 4 Portable Transistor Tester AB C F This low cost type of transistor tester uses digital high c
33. 5 INTEGRA j 9M T TOR RS BASELINE IUNIPOLAR RESTORER CE 1 x SHAPING SECTION La Past i i PILE UP DISCR CHANNEL REJECTOR 1 i i 9 x adeuo Chapter 6 32 To troubleshoot a faulty spectroscopy amplifier start applying at the input a 1OmV square signal with a 2KHz signal and set on the relevant panel knob a value of the gain around 500 Connect the output of the amplifier to an oscilloscope through a 2m long cable In this condition you should see on the scope a sequence of positive and negative gaussian signals of about 5V in amplitude and related in time to the LOW TO HIGH and to the HIGH TO LOW transitions in the input square wave Use of a two channel oscilloscope displaying in the ALTERNATE position the input square wave and the output gaussian signals is appropriate If the signals are present at the amplifier output synchronise the scope on the channel displaying the output signals wake a Single gaussian pulse firmly visible on the display and proceed to the following tests a Switch the COARSE GAIN knob through all its available positions and make sure that the signal never disappears on tne scope and that simply its amplitude changes according to tne knob setting If for a given position of the COARSE GAIN knob the signal disappears or looks to be badly deformed check the condition of the resistors and in that
34. ARTIFICIAL PULSES performance degradation a b c gt appearance of a small non linearity slight increase of noise rise time d SPECIFIC TESTS time jitter and so forth _ 6 1 1 Visual Inspection Visual inspection aims at discovering whether a there is any stray jumper shorting two wires b there is any resistor which because of a change in colour or a deformed shape suggests that the maximum ratings have been exceeded c there is any cold looking soldering d there is any wire or component pin disconnected NOTE The instrument under repair should be illuminated by an intense lamp Even if you have good eyes a magnifying lens can help you to see more details 6 1 2 Checking dc Conditions If the visual did mot reveal any faults proceed to the next step namely to check dc conditions throughout the instrument 106 Chapter 6 NOTE The analysis of de conditions if done properly will help you to detect the fault in most cases Several precautions must to be taken during a dc analysis 1 Check the condition of the fuses if the instrument to be repaired is supplied directly from the mains Then remove the cover and after turning the power ON check that the supply voltages are present at the correct values on the output lines of the power supply If the instrument to be repaired is a module which receives the supply voltages from a cra
35. DATA LEADS Pin 2 is used for transmitted data and pin 3 for received data Data are transmitted over pin 2 from one machine and received on pin 3 at the other To allow for proper data transmission and reception at both machines cross pin 2 on one end with pin 3 on the other end Function PCl Pin DTE PC2 Pin DTE Function PG l gt 1 Protective Ground SG 7 lt gt 7 SG Signal Ground TD 2 Oe TD Transmit Data RD RD Receive Data Data terminal equipment DTE provided signals are all that are present in a null modem cable This limitation forces us to provide DCE signals with available DTE signals Specifically the DTE signals RTS and DTR must used to provide or emulate the DCE provided signals DSR TS and DCD Data Terminal Ready DTR pin 20 is ordinarily provided by the DTE to indicate that power is on at the terminal For an indication that the line is established the DCE normally gives a signal on pin 6 Data Set Ready DSR As long as DSR is on one can assume that DCE is available for data transmission If pin 6 is not present the line or connection is not available To emulate DSR pin 6 at both ends we strap the DTR signal pin 20 at one device across to pin 6 on the other device The same strapping is done in the other 213 Chapter 10 4 direction By strapping pin 20 across to pin 6 whenever DTR is high the machine power is on
36. In contemporary systems the digital part operation is steered by a microprocessor reading the operating instruction from a large ROM Read Only Memory The measured data are stored in the RAM For the CRT display a system similar to a television screen is used For effective repair you should become familiar with the multichannel analyzer operation Troubleshooting instructions cannot describe every detail some imagination is required Useful information on the operation of the multichannel analyzer can be obtained from the publication IAEA TECDOC 363 Selected Topics in Nuclear Electronics pages 117 168 The general instruction would be out of place here Therefore we will concentrate our attention typical MCA Canberra 35 Plus Fig 9 2 173 Chapter 9 21232 Analyzer Sianal Operator Memory Display gna Data 1 0 Processing inter face Fig 9 2 Block Diagram of Ser es 35 Plus MCA 9 2 MCA TROUBLESHOOTING AT THE UNIT LEVEL 9 2 1 Low Voltage Power Supply We have removed the top cover of a CANBERRA 35 Plus MCA The location of individual printed boards is indicated in Fig 9 3 If after 20 seconds the screen is still black the power supply should be checked On the power supply board are 5 LEDs in line all lighting if supply voltages are present This voltage can be measured between the ground at TP7 and to TP6 L V SUPPLY DISPLAY MONITOR GND TP 12 TP2 5 TP6 15
37. Q103 The central tap of the transformer is connected to the emitter of Q103 while its collector is on the positive pole of the battery The base potential of this emitter follower is driven 0104 The base of 010 is connected to the rectified output signal of the transformer through the R131 potentiometer and the reference diode CR103 to form an adjustable feedback controlled regulated voltage circuit If the output voltage is not 12 volts the fault causing it should be determined and eliminated Let us suppose that the symptom is no voltage on the 12 volts rail First the detector should be detached from the central unit If the voltage appears then the problem is in the removed section If the voltage does not appear a quick way to locate the fault could be done by separating the central tap of the transformer from the emitter of Q103 and with an ohm meter check for shorted collector emitter condition in Q101 and Q102 If there is no short circuit one should apply 4 to 8 volts through a fused ammeter for a short time If the oscillator starts operation and the current is less than 50 mA a volt meter should be attached to the collector of 0104 This point should be near to battery voltage if the R131 potentiometer is grounding its base and it should start conducting if the potentiometer is put into the other end position If no change could be observed all components should be checked one by one and the bad ones must be r
38. The indirect test is done by observation of the 1 MHz clock derived from 6 MHz clock at test point 8 Another indirect test is to observe CK signal of 3 MHz leaving the 8085 at TPlO However for the direct check your probe should be attached to pin 1 of 8085 big chip A45 position 188 17 Chapter 9 The 8085 system bus is created by using A40 and A47 8282 INTEL production similar to 7415374 but different pin config uration to latch the 16 bit addresses Latch is performed using the A signal derived from the ALE microprocessor output A signal can be observed at TP11 See Fig 9 18 for the block diagram INTR Status Decoder BADO BAD7 TURZC MOTION CONTROLLER 16K or 32K Byles RAM OCHA DCHA DATAV REQEN A8 A15 Fig 9 17 CPU board structure Fig 9 18 8085 system bus and data flow 189 Chapter 9 18 Bidirectional data flow is provided using the 3 state bidirectional drivers 7415245 A61 and A62 A61 output is enabled by RDROM signal observe TP17 and the direction is selected by DI available at pin l A61 The A61 data flow direction is selected by a signal which can be observed at TP15 Three state operation is not used i e 19 is grounded The status decoder A39 produces the input output control signals WM at TP9 RM at TP13 OE at TP12 and a few others When working with the slow input or output devices a WAIT State should
39. They often develop short circuits within the secondary Local repair is possible if proper interlayer insulation could be secured combined with vacuum impregnation If R110 the 22 MOhm value feedback resistor fails to conduct a dangerous situation might develop The missing feedback voltage forces the circuit to increase the output so a higher than normal voltage will soon be established on C105 and the Geiger Mueller tube will behave accordingly The reverse leakage current of the CR106 can be 30 100 mA only so a dangerous charge might remain on the C105 capacitor for a long time after the instrument was switched off the 0 01 J energy kick can hurt Care should be taken to check the presence and good condition of the feedback resistor before starting the repairs The Geiger Mueller tube is in the center on its right side a pulse shaping circuit can be found If the Geiger Mueller tube is triggered a positive pulse will appear on R204 limited to battery voltage amplitude by CR201 clamping diode The pulse is differentiated by C201 R204 before it enters Z201 a monostable multivibrator generating equal amplitude and length pulses After further amplification in Q202 the signal leaves the sonde through emitter follower 0201 The connecting cable is rather critical in portable instruments It should be checked thoroughly for continuity and wear It is better to replace the worn cable before a fault develops 254 Chapte
40. a voltage higher than 30V DC is applied to power input or when power lead is connected reversely or with AC line ABC F 53 Chapter 3 3 3 16 Digital Circuit Tester A Pulse shorted node Shorted Current Tracer Follow current puises to short Stuck Data Bus Current Tracer Pulse and probe test point simultaneously Short to or Ground cannot be overndden by Probe Current Tracer pulsing Pulse test and follow current pulses to the short Remove power from under test Disconnect electrolytic bypass capacitors Pulse across and ground using accessory connectors Provided Trace current to fault Pulse device nput s Probe output for response Pulse suspect kne s Trace current pulses to the fault Light goes out when solder bridge passed Cvcut clock de activated Use Pulser to enter deswed number of pulses Place Clip on counter or shet repster and verity dence truth table Signal Line Short to Vee or Ground Supply to Ground Short int Open ernally 54 Curent Tracer Current Tracer Stimulus response capability circuit and testing kit in dynamic multi pin complete multi family fault static finding testing To accomplish troubleshooting at the node and gate level both stimulus Pulser and response Probe Tracer Clip and Compara tor ins
41. and a repetition rate of between 10 Hz and 10 kHz 247 Chapter 11 For the calibration of the counting rate meters one should have a scaler with a reasonably accurate time base The mains frequency in most countries is not suitable for this purpose In repair of ionization chamber systems a 10 kOhm multi turn potentiometer with micro dial can be a useful repair aid to simulate the detector as shown in Fig 11 6 Ga Resistor MULTI TURN POTENTIOMETER USED IN TESTING Fig 11 6 The technique of electronically simulating a radiation detector In testing DC DC converter transformer shorts the ohm meter could give information only on very crude faults A more sensitive approach is when the ohm meter is connected into the collector circuit of transistor minimum beta 45 in series with the primary of the transformer under testing The secondary should be in the base circuit to form a blocking oscillator as shown in Fig 11 7 Note the correct coil connection directions symbolized with the dots TRANSFORMER UNDER TEST OHM METER Fig 11 7 A simple tester for DC DC converters 11 1 4 5 Identification of the ke oints signal simulation DC voltage measurements or pulse shape observations in the key points aid the repair efficiency the quick diagnosis of the fault 248 9 Chapter 11 If the battery of the survey meter is bad no functions could be expected from it So the first key test po
42. complicated circuits built up from these simple ones The dotted lines in Figs 6 1 6 2 and 6 3 imply connections to other parts Sometimes an instrument undergoes a catastrophic failure owing to which in the individual elementary circuits like those of Figs 6 1 through 6 4 more than one component be damaged There are so many possible combinations of faulty elements that troubleshooting may require a procedure describing flowchart A flowchart will be developed here with reference to a single transistor circuit of broad validity the one shown in Fig 6 6 To judge whether this circuit is properly operating or not the voltages VB VC VE to be measured and compared with the nominal values 113 Chapter 6 10 ElR2 E2R1 VE VB 0 7V Rl R2 VC El VE E2 R3 R Fig 6 6 Basic transistor stage If the measured values differ from the nominal ones by more than 10 which accounts for the worst case component tolerances the circuit has to be considered faulty As previously pointed out the fault may be due to either 1 defective voltage divider 2 defective transistor 3 defective emitter resistor 4 defective collector resistor or 5 defects in layout or to all the possible combinations of two three four or five causes of fault Referring to the circuit in Fig 6 6 immediately removes any doubt about whether the fault depends on the voltage divider or on the active device
43. gI g 1 3dey9 Chapter 9 MULTICHANNEL ANALYZERS 1 Chapter 9 9 MULTICHANNEL ANALYZERS 9 1 INTRODUCTION The most frequent task of a multichannel analyzer is to search for the pulse height distribution of the incoming pulses pulse height analysis PHA In order to get the pulse height distribution or spectrum the pulse height of each pulse is measured and the result is expressed as a binary number This is the task of the ADC unit The measured binary number serves as an address to the random access memory RAM location The contents of the called memory location is pushed into the ADDER where it is increased by one The new number is returned to the same location As a result of this procedure the RAM can tell how many times pulse of a given height has appeared during the measurement The whole operation is controlled by the steering logic Fig 9 1 ADC ADD Fig 9 1 Simplified MCA During the measurement or after it results are either displayed by the CRT and or transmitted to a peripheral device like printer or plotter The display is always a part of the system while external units are connected according to our requirements Communications with an external printer or plotter are realized either the serial RS 232 interface by the parallel Centronics In order to perform the described tasks a rather complicated system composed of the analog part followed by the digital one is used
44. in Fig 6 11 119 Chapter 6 EU s R3 TO 175 NONINA L VALUE DISCONNECT THE NOMINVELTING rut OF THE OPERATIONAL ANPUFIER FROM i DINDER AND CONNECT it TO 70 ITS NORA ER h bota tle APPLY THE VOLTA Mee 0 0 Fuu SROET CIRCUITS INTER Qu on OMS varout r OF ANP CONNEC NAL oF RESISTOR Ra SUPPLY VOLTAGE amp TERM 0 NOMINAL VALU E R e R 22 NO THE TROUBLE SHOOTING PROCEDURE TO NO FURTHER dc ANALYSIS REQUIRED RE Bn Pett pri Xi du doen if THE WERNE PUT OF Of AnP P Va USE TO TS gt WO we N RESTORE amp ow CONU CCT T ARPUMER Ho rut TH f ec AVAL TSS acquired Fig 6 11 Flowchart for troubleshooting a basic operational amplifier configuration 120 17 Chapter 6 6 1 4 Signal Analysis Have you finished the dc analysis of the individual parts of your instrument Have you made sure that everywhere in the instrument the dc conditions meet the expected values If so you can quickly check whether your instrument implements its basic function For instance a If the instrument is a preamplifier or an amplifier does a signal a
45. is a long and difficult procedure It is very difficult to teach troubleshooting and repair any instrument In fact the acquisition of the necessary experience for repair of electronic and electromechanical instruments is a typical case where on the job training is most effective As rule one should not take the methods that the manufacturers apply to train their field engineers their training is limited to a certain line of products or even a single instrument and for this they have developed efficient approaches to convey the required skills in a short time The staff of a service laboratory in a developing country cannot be trained in this manner on all possible types of equipment which there might be only one installed in the country Their approach to the servicing and repair must be more general and is more demanding In the nuclear field the staff responsible for instrumentation maintenance and servicing face a number of additional problems i Nuclear electronics is not taught regularly at the universities or technical schools in developing countries ii Literature on nuclear instrumentation and particularly on servicing of such devices is scarce or non existing 9 Chapter 1 x2 iii Manufacturers information on their products and servicing is generally either bad incomplete or not available iv There are very few experts who are familiar with the repair of nuclear instruments v A talent
46. pin 10 will force multiplexing diode D20 into conduction therefore fixing the output of the MUX the common point of 020 and 021 to logic 0 and thus also disabling the counting of event pulses If jumper A is moved to the B position the external gate signal cannot disable counting The external gate also actuates on the time generator by closing Al3d provided jumper 5 is in the appropriate position thus time counting can be controlled in lys intervals Note that A45c is actuated through A45b being open when the output of A45b is at logic 1 this requires pin 5 of A45b to be at logic 0 a condition that is satisfied as discussed below 8 3 4 Start Stop and Enable Circuitry The start signal from the START input or from the manual switch sets flip flop A3 While the flip flop is set counting is enabled except for an initial lOus dead time period set by the A24 monostable to reset the A51 six decade counter To allow a reset to follow quickly the set signal should be narrow this is accomplished in the manual starting mode by keeping pin 2 of 13 only momentarily at logic 0 only while R15 charges up C5 Through the output of Al3a the start signal triggers the 10us 24 monostable to clear the A51 counter and to enable the parallel load of the 42 and A43 down counters Note that a 10ps dead time is thus introduced in the counting t me The output of the A3 flip flop is ANDed with the preset count signal output of A6c
47. stone CEGTEASZO 4 xot X SY X OW CAP WEM we is PVC antistatic e s s s 4 s e e s o o n Colour green grey uni 5 Chapter 3 3 1 2 Work Benches work bench with additional shelf of beech material solid construction permissible load 100 kg min non inflammable surface preferably with drawers and additional shelves us DUE wey E dL UE le LET AURA See IE Uh 28 with antistatic bench mats two for each working place with and without backplate at least one with adjustable height and rolls en ge far Te E 3 1 4 Bench Lights adjustable in all directions arm length min 80 cm we Se ek as Fe Sei be fluorescent lights and lenses e 7 halogen lamp spot light min size 60 x 7O cm min load capacity 60 kg should have the same height as the working table s s ABC A B C Q5 Chapter 3 6 3 1 6 Shelf preferably a modular system with pillars adequate to the room height precaution shelf must be anchored to the wall at a reasonable height V ria 3 tec e 3 147 Cupboard solid preferably metal lockable with drawers and adjustable shelves metal frame with plastic drawers drawers with an edge to avoid inadver tant withdrawal 3 1 9 Storage Boxes different sizes plastic stockable mainly f
48. 100uA and the circuit is simple to understand NOTE NEVER measure with a digital voltmeter in the HV path unless you use a HV probe with a voltage divider 1000 1 such a high voltage probe is available from Fluke or 100 1 Through such a probe the input resistance of a digital voltmeter is 10000 MOhms Another possibility is to use a static voltmeter but pay attention to HV isolation problems HV bias supply is usually built around a DC DC converter An oscillator push pull circuitry a transformer and a regulation circuit are necessary on the primary side on the secondary side the AC is rectified and filtered or a voltage multiplier may be used Before you start troubleshooting make sure that the working area where the HV supply will be tested is free of all conducting material such as wire ends etc to prevent HV shock hazards 5 6 1 1 Troubleshooting The specific HV bias supply described here has no feedback loop Be sure that all required input supply voltages are provided Using an oscilloscope check that the oscillator 91 Q2 is working Frequency can be changed with potentiometer R42 If not check Ql and Q2 The next step is to inspect the operation by measuring with the voltmeter the emitter voltage of transistor Q7 while changing the front panel potentiometer R23 Increasing the setting of the potentiometer should induce the voltage change of the emitter voltage of transistor Q7
49. 2102 drives the moving coil type display meter Ml through resistors R113 and R129 serving for full scale adjustment The alarm circuit starts to operate above a level which can be set with the Rl potentiometer Checking can be done by injecting a variable voltage through a 10 kOhm resistor to the inverting input of 2102 if the operational amplifier output does not change it must be replaced The second half of the 2100 generates the alarm signal frequency and 0106 is the power stage driving the loud speaker LSl 11 1 5 Stock Faults in Various Systems and Repairs Symptom Cause Action New dry batteries corroded contacts clean if needed replace Test no indication faulty switch clean if needed replace meter or R113 bad repair or replace short circuit determine location repair Test low voltage short circuit determine location repair R129 misadjusted readjust R129 corroded contacts clean if needed replace 258 Chapter 11 19 amat may s i u N mn wai am I ec rM ma SSS ui MER Maa EA 3 TA i z 259 Ratemeter and alarm circuit 11 12 Fig Chapter 11 Ni Cd accumulator low voltage No 12 volts More than 12 volts Less than 12 volts Geiger Mueller sonde No 12 volts No detector supply Detector supply high No signal with source 260 20 charger fuse bad cell
50. Diagnostic tests in the M I P 10 polyradiametre The M I P 10 is a portable battery or mains operated survey meter equipped with various types of nuclear radiation detectors It can be used as a dose rate monitor if calibrated 250 11 Chapter 11 i Controls and display The picture of the front panel is shown in Fig 11 8 main switch battery test loud speaker on off and four counting rate meter range selector push buttons form the controls of the instrument The moving coil type display has two scales one for the battery condition indication and the other for the CRM readout O nain 4 Fig 11 8 Front panel of a typical survey meter ii Connections The detector socket is on the front panel line voltage recorder and scaler outputs are on the rear side with the mains fuse 111 Battery operation Eight 1 5 volt batteries can be loaded into the battery compartment In an optional variant a rechargeable Ni Cd supply is available with a drip charging feature The wiring diagrams of the two variants are shown in Fig 11 9 The first key test point is the battery voltage between pin 1 and 11 This can be tested with the built in TEST push button If new batteries were put into the instrument and the TEST gives no indication to the moving coil meter the Sle switch has to be tested for continuity Sometimes corroded battery compartment contacts create problems they must be cleaned or replaced as neede
51. Even so one has to realize the fact that the on site service of highly sophisticated nuclear instrumentation may often have to limit itself to the board level just by swapping boards Board test equipment which is required to enable repair the chip level will only be affordable to the instrument manufacturer some strategically located service centers worldwide One may complain about th s situation but it also offers a considerable advantage by reducing the number of boards in typical nuclear instrument and consequently the failure rate Many manufacturers are now able to use a functionally partitioned approach to break down a design to the board level which allows them to provide diagnostic routines and facilities to the customer for easy fault location to the board level 15 Chapter 2 4 Special emphasis should therefore be given to this fact when ordering equipment if such diagnostic facilities are available In such a case return of an instrument to the manufacturer may never be necessary and the possibility of shipping damages when returning a board to the manufacturer largely vanishes Of specific importance for service laboratory is the availability of suitable extension boards and cables If they cannot be purchased they must be produced in the laboratory Another essential activity of a properly organized laboratory is the good organization of the technical library This should include Original
52. MESSAGE PULSE SENT TO THE COUNTER BOARD DURING STATE 5 IF RECYCLE IS SELECTED FROM ACCEPTOR HANDSHAKE TIMING FROM REMOTE LATCH BUS GENERATED WHEN ENABLED SENDS A STOP PASE TO THE COUNTER ON DCL COMMANO FROM THE BUS D D 10010100 inputs MA MY ADORESS FROM MY ADORESS DECOOER 07 DATA 6 BUS GENERATED 10 10 Remote Lain OVA DATA VALID FROM ACCEPTOR HANOSHAKE TIMING outs evc BYTE CLOCK FROM SOURCE HANDSHAKE TIMING Cx CLOCK FROM INTERNAL CLOCK HAVE IT FROM SOURCE HANDSHAKE TIMING RSET RESET FROM RESET CIRCUIT iB LAST BYTE FROM OUTPUT DATA SEQUENCER MA MY ADDRESS FROM MY ADORESS DECOOER ABRT ABORT FROM RESET CIRCUIT OVAL DATA VALIO FROM ACCEPTOR HANDSHAKE TIMING TON TALK ONLY MOOE 5206 O68 D DATA6 7 BUS GENERATED 07 06 100901 ECO END OF COLLECT FROM COUNTER BOARD Outputs Outputs REM REMOTE ACTIVE AFTER HAVING RECEIVED MY RCE READ CLOCK OUTPUT TO COUNTER BOARD LISTEN OA MY TALK ADORESS FROM THE ENABLE TO ENABLE RCL BUS INACTIVE AFTER RSET MTA MY TALK ADDRESS ACTIVE AFTER BUS COMMAND MTA INACTIVE AFTER DTA OR UNT BUS 1 Reset Cram COMMANDS CLEARED ON LB AND HVIT inputs POWER ON ACTIVE AT POWER ON 51 My Aaacress Decoder FC INTERFACE CLEAR BUS GENERATED inputs TON TALK ONLY FROM 520 6 05 OA A 5 BUS GENERATED REN REMOTE ENABLE BUS GENERATED 520 1 ADORESS BUS ADORESS SELECT SWITCHES Outputs 520 5 SWITOES BINARY WEIGHTED 6 ABORT ACTIVE AT POWER ON OR DURING IFC NOTE All swaches on adores 31 CLEARS MY T
53. O With a scope it should be observed that the outputs of the comparators go to the complementary logic state while the analog signal exceeds the respective comparison voltages 7 2 3 The SCA Logic and Timing Circuits The SCA logic is mainly based on RS latches made with gates included in Al A3 A5 and on gate A2b You may quickly perform a first check on these and the other latches present in the circuit by just observing if their outputs Q and Q are complementary as they should be The logic behaves in somewhat different way according to whether the leading edge or the crossover mode is selected We first refer to the leading edge mode operation which may be checked as follows Apply pulses of about 5V amplitude and with a shape similar to lus amplifier pulses Set the baseline helipot to a level of about 4V and the channel helipot to a channel width of 2V only the baseline discriminator should be triggered by the input pulse Look at the timing discriminator All output pin 5 observe that it changes before the baseline discriminator output because it is set to a trigger level of around 0 2V while the baseline discriminator level is set at about 4V Note that for All to be triggered it is necessary that pin 4 be at logic 1 the state at 4 is controlled by latch A4 pin 6 You may now observe the actions initiated by the output pulse of All Through inverter 919 it triggers monostable A5b the complemented roughly O lus w
54. R3 R4 Mind the following 1 If the voltage drops across R3 or R or both are zero but the one across R is equal to El E2 then R3 and R4 behave as short circuits The short circuits may depend on the resistors themselves or on some stray jumper on the layout Check the latter possibility by accurate visual inspection If there is no evidence of stray jumpers proceed to replace R3 and R4 and check the voltage drops across the R3 R R4 divider again Most likely the fault has been eliminated 253 If the voltage drops across R3 R R are all zero there is a circuit interruption along it Again this may depend on R3 or R or both being interrupted or on some broken connection on the layout Search for it by accurate visual inspection and if you discover any defective connection repair it Otherwise again replace R3 and R and check the voltage drop across the R divider again Either way the fault should have been eliminated Once you have removed the transistor and made sure that defect had to be attributed to R3 and R or if there was a defect that it has been fixed proceed to check the transistor 115 Chapter 6 12 NOTE The most reliable procedure would be to test the transistor with transistor curve tracer This instrument will tell you whether the transistor is still alive or definitely gone but would also enable you to determine whether a deterioration in its characteristics has
55. This process is repeated every 10ms and an appropriate interrupt is generated when a key is pressed This interrupt is done by a return signal appearing a column line Note that special function keys such as SHIFT and CONTROL do not form part of the matrix These higher priority keys are treated separately as direct inputs to port A 233 Chapter 10 24 Fig 10 11 Keyboard coding arrangement using a 8255 PPI Now let us assume that there is something wrong with your keyboard interface how do you start troubleshooting First try to find out if only one of a group of keys is not working or if the whole keyboard is not working This may be seen by pressing related keys in the keyboard If your whole keyboard is not working check the supply voltage Take an oscilloscope and have a look if scan pulses appear on PCO to PC3 If they do look at the decoder output to see if this is working Pulses should appear on lines 0 to 15 Next check if the pulses are connected through to the inverters and PBO to 7 by pressing the related keys Check the special function keys at PAO to PA3 If you find that up to now everything works correctly you can assume that your controller is defective But before changing it make some more tests on the bus side of the controller If you find that on the peripheral device the keyboard works properly and that writing to the PIA is correct then there may be something wrong with the read
56. Type of preamplifier optical or resistive feedback I2 1 2 Installation and Testing of a High Resolution Detector The high resolution solid state detectors are shipped together with the dewar but without liquid nitrogen except if the customer specifies otherwise A pure germanium detector and a modern Si Li detector can be stored for years at room temperature without loosing their characteristics Before put into operation the dewar of such a detector must be filled with liquid nitrogen and the detector cooled for a period of 4 to 6 hours The manual of the detector specifies the minimum time for cooling and it is advisable to adhere to the recommendations of the manufacturers With each solid state detector the customer receives a certificate describing the properties of the detector and the conditions under which these characteristics have been determined An example of the certificate in this case for a Si Li detector is given in Fig 12 1 When determining the features of the detector one must try to reproduce as close as possible the measuring conditions given in the certificate A general observation is that the manufacturers are rather conservative with the specifications presented in the certificate With careful adjustment of electronics and correct measuring procedures the value given by the manufacturer can as a rule be easily achieved and surpassed Before you start to write angry letters to the company that sup
57. a dc level should appear If not change the IC On the collector of the power transistor 010 and Q102 you should measure 24V when the instrument is switcned off If not there must an interruption in the HV module After switching on the instrument a sinusoidal waveform should appear with the amplitude depending on the HV voltage setting If not the HV module is defective and must be replaced by a new one The HV module consists of transformer voltage doubler filtering network and feedback resistor chain and is sealed that no humidity can reach the components If for any reason the feedback loop is interrupted an over voltage detection is activated and shuts down the instrument For test purposes it is necessary to disconnect or remove diode CR109 5 7 SWITCHED MODE POWER SUPPLIES Nowadays the so called SWITCHED MODE power supplies are frequently used This type of supply has some advantages an important one is that they are smaller and lighter compared to the linear regulated ones They are frequency independent 40 400Hz over a wide range and the voltage variations range covers from 10 to 20 of the nominal line voltage The efficiency of such supplies is in the order of 75 this means less heat production On the other hand there are also some disadvantages lot of filtering is absolutely necessary otherwise this supply would be very noisy The load regulation is critical From the theory of matched o
58. accordingly Some situations and actions scanning line wise border switch activated step wise motion starts after this new line scanning starts with reversed direction step wise border switch activated scanning is finished all motors are stopped border limit proximity switch activated motor torque is reduced breaking action starts before scanning direction is reversed this action is important otherwise the mechanical system is exposed to heavy strain safety limit switch activated further motion in same direction is inhibited Under the manual detector positioning mode only the safety limit switches are active in protecting the mechanical system 11 2 4 8 Stepping motor control circuits The block diagram of the circuit is illustrated in Fig 11 18 The step frequency selection is done by the SPEED control switch In a phase splitter double phase signals are generated from the step frequency signals to feed the rotation direction control circuit together with the line wise border limit switch information Whenever a border limit switch is activated the bi stable multivibrator sensing it changes the phase of the triggering pulse to the triac which drives the rotation direction control coil of the motor The motor torque is always reduced to zero before the rotation direction is reversed by modulating the firing angle under the control of the limit proximity switch 274 35 Chapter 11 The
59. an output indicating that the HOLD command has been accepted TRAP interrupt is edge and level sensitive and must remain at a high level until it is acknowledged It is non maskable there is no software way to avoid it when the signal is applied to the input When the interrupt occurs the address is branched to 24H RST 7 5 RST 6 5 RST 5 5 These three inputs have the same timing as INTR except they cause an internal restart to be automatically inserted The resulting addresses are 3CH 34H and 23H respectively INTR interrupt request has a similar effect as TRAP and RST with the return address depending on the instruction read by the CPU when interrupt is acknowledged NOTE We only discussed the function of the pins used in the described application of 8085 9 5 GENERAL STRUCTURE OF THE CPU BOARD Microprocessor 8085 has to be supported with some additional units to form the complete computer system However because of the request for direct memory access more than minimum additional circuits were added See Fig 9 17 for the block diagram of the CPU board The complete schematics of the CPU board are covered by 6 sheets RAM organization ROM organization Cursor motion controlling system 8085 processor with bus lines and status decoder Direct memory access controller central clock unit Remote control interface un FUNG 9 6 8085 COMMUNICATION To check the 8085 operation starts with 6 MHz clock inspection
60. and associated resistors If VB is at its nominal value the fault has to be attributed to the active device and or to the R3 R4 resistors If however VB is not correct the voltage divider or the T R4 amplifier or both may be defective To disentangle responsibilities remove the transistor and check VB again If VB is near its nominal value then the fault has to be attributed to T R3 R As T was removed you have a very effective way of checking R3 R4 Fig 6 7 Connect in series with and R4 amp a resistor of accurately known value and such that the current I flowing across the series connection R R I El E2 R3 R R will be equal to the current IE IC which would flow across transistor T and resistors R3 R4 if no fault were present Such a current is easily evaluated from the table of nominal values 1 114 11 Chapter 6 IE IC x VE E2 VB 0 7V 2 R R Fig 6 7 Replacement of a transistor by a resistor Besides R must be able to stand a power of at least 5 El E2 2 R Once R is connected check whether or not the voltage drops across R3 R4 coincide with the nominal values determined by the knowledge of I and of the nominal values of R3 R4 If they coincide then R3 and R are not defective and you can focus your suspicion on the transistor If however any none of the voltage drops across R3 R4 stick to their nominal values concentrate on
61. be inserted into the normal instruction cycle The READY input is suitable for this controlled by A25 and A26 After the direct memory access request the normal microprocessor operation should be restored This is done using RST 7 5 and RST 5 5 input lines of 8085 The general power failure is indicated by a LOW on PWRF line After the inversion in A60 the TRAP input highest priority is activated 9 7 ROM OPERATION ROM organization is given in Fig 9 19 The ROM circuit is divided into four banks of 16 x 8 bits for a total programme memory of 64 kbytes This is also the normal addressing space of 8085 Because we also need RAM for data storage the programme controlled bank switch was introduced The signals and BK2 are stored in latch All Tri state driver A48 is enabled if BK1 is low address bit Al4 is low Driver A29 is enabled if is high and if the address bit A14 is high Signal BK2 is gated with address bits Al4 A13 and Al2 in a 74LS10 location 10 to determine which ROM output 15 passed through driver 48 The selection of the separate ROM chips is realized through 3 to 8 line decoders 74LS138 14 and A78 190 19 Chapter 9 Fig 9 19 ROM organization 9 8 RAM OPERATION RAM consists of four static RAM chips 8k x 8 bit each Because of the low power consumption memory chips can be powered from the built in rechargeable battery for up to 30 days The data exchange goes through thre
62. be plotted on input frequency vs displayed value relation Action should be taken if the integral non linearity exceeds 5 A pulse generator is an essential instrument in the diagnosis of counting rate meter faults 11 2 4 5 Colour adjustment potentiometer The most often used control element of the scanner is the potentiometer between the counting rate meters output and the input of the intensity to colour converter servo circuit It must be adjusted so that the maximum activity area should appear in red colour on the scintigram An early sign of wear of this potentiometer is if the colors are changing while the count rate remains constant during tests with a source fixed to the detector 11 2 4 6 Intensity to colour code converter servo The circuit diagram and mechanical construction of a typical converter is shown in Fig 11 17 In its simplest version the position of the coloured typewriter ribbon under the tapper is sensed by a potentiometer mechanically attached to a DC motor The non inverting input of the operational amplifier is connected to the source of the intensity information that is to the counting rate meter output through the colour adjustment potentiometer The inverting input is connected to the moving contact of the potentiometer while one end is on ground and the other on a reference DC voltage level The DC motor is connected with such polarity to give negative feedback that is the voltage from the poten
63. broken R201 bad Z201 R401 badly adjusted short in Tl diode short in voltage multiplier CR102 111 capacitor short in voltage multiplier Chapter 11 replace bad components replace repair decontaminate repair DC DC converter replace locate repair repair DC DC converter G M repair replace tube locate repair replace repair locate repair repair or replace replace replace replace replace replace readjust replace or repair locate replace locate replace 261 Chapter 11 No scintillation detector output signal with stan dard source in reference posi tion TP 1 Pulse rate higher than normal in reference con dition Pulse rate lower than normal in reference con dition Main unit count ing rate meter not functioning in reference mode Counting rate meter calibration bad in single range 262 22 dynode resistor chain element broken photo multiplier bad Z203 or Q204 bad C211 broken radiological con tamination noise pick up from DC DC converter noisy photomulti plier corona discharge on high voltage component humidity caused high leakage current increased background in workshop high voltage too low deteriorated scin tillator R222 broken C301 303 broken no signal from sonde cable is bad connector is bad Z100 bad Z101 range switches R104 106 R124 127 or C106 109 bad bad adjustment or faulty R C c
64. control line If RD appears as well we may think in two alternatives first the PIA is bad second it was wrongly initialized so that the ports are not set properly Maybe your software is causing the trouble So write a 234 25 Chapter 10 small test programme which initializes the PIA and so that you can test each PIA line separately 10 7 STEPPER MOTOR DRIVE Frequently an interface application will require that the PC controls the motion of object A device that is often used to power or move a shaft in precise increments directions and speeds is a stepper motor Here we consider two approaches to this problem The first uses the stepper motor a device whose angle of rotation is known reliably from the pulses which have been sent to it Once calibrated and initialized no feedback of the rotor s position is necessary unless the speed demanded is too high or the torque required is too great Running a motor this way without feedback is called OPEN LOOP The second method uses feedback is a CLOSED LOOP approach and is called a servo system The servo System can respond more quickly and accurately than the open loop stepper motor system and is relatively insensitive to hardware variations However it requires position sensors as well as more complicated drive electronics to ensure stability Next we have to distinguish between two different ways of driving the motor The first method is to implement the stepping seq
65. digital multimeter DVM Co What am I going to connect slave Is it data communication device like a printer a terminal Am I going to control different instruments like DVMs scaler timers MCAs Do I have to control peripherals such as sample changers or motors 211 Chapter 10 2 d Are interfaces already available in the master If YES can I use them for the job I am going to do If NO what is available from the company or on the market e Is an interface already available in the device the slave I am going to connect f If interfaces are available in both the master and the slave are they compatible ATTENTION Make your decis ons very carefully you will have less trouble later on 10 3 SERIAL INTERFACE RS 232C V24 The application of the RS 232 interface is widespread in mainframes minicomputers microcomputers printers and all types of terminals It is used for a SERIAL BINARY DATA INTERCHANGE between two devices The basic principles of the standard are implemented in such devices however various options may occur from device to device These variations become extremely significant when interfacing different combinations of computers printers and terminals A general rule may be established follows NOTE When connecting between devices make sure that an output signal goes to an input signal and vice versa First of all terms which are used for
66. displays all digits should be permanently activated circuits including a 4 bit latch and a converter for each digit are generally used Scanning circuits are typically made out of a binary counter and a decoder for example 1593 and 15138 whose output lines successively activate the open collector or tri state circuits that connect the various decades to the bus and select the appropriate digit Some LSI circuits like the six decade 7301 already include the scanning circuits 8 1 7 Time Generators In timers or counter timers time marks are derived from the mains typically at 1 100 or 1 120 second period or most frequently from a crystal oscillator These generally oscillate at a frequency of several MHz which is suitably divided to give time marks either in a seconds or in a minutes scale In preset type counter timers the preset count can be associated with either the counting events or the time marks 8 1 8 Ratemeters A typical digital ratemeter has a structure similar to that of a preset counter timer The integration period corresponds to a preset time the displayed count corresponding to the total count of the previous period is updated once per period Analog ratemeters typically shape the input pulses a well defined form and integrate them toO have a voltage proportional to the incoming rate in either a linear or in a log scale 8 2 TROUBLESHOOTING The first step in troubleshooting is to e
67. drop because there is no load It could be that due to bad adjustment of the output voltage the crowbar trigger level has already been exceeded Remove IC U2 and check again If the voltage drop is again too high check the value of resistor R5 may be broken or value change due to overload If the value of R5 is correct remove thyristor Q2 and when pulses occur replace thyristor When the output voltage comes back a bad adjustment of the output voltage may be the reason for the shut down or a defective IC U2 Measure the output voltage of the module and adjust with potentiometer R13 If the adjustment is not possible check the feedback loop If this is OK replace IC Ul If there is no output voltage connect the oscilloscope probe to common and look at the diode bridge Dl pin 1 this diode looks like a power transistor Pulses must be there if not either transformer Tl capacitor C3 or switching diode D3 is defective To find the defective component the components must be removed from the circuit If pulses are observed but still there is no output voltage the components D2 Ll may be faulty or one of the capacitors C5 C6 may be shorted After these checks the output voltage should be there Measure and if necessary readjust output voltage Insert IC U2 check again if no output voltage is present replace IC U2 102 Chapter 6 PREAMPLIFIERS AMPLIFIERS af Chapter 6 6 PREAMLIFIERS AMPLIFIERS 6 1 GENERAL ASPECTS OF
68. feedback and input FET operating at room temperature is analyzed 6 2 1 1 General considerations typical block diagram of such a preamplifier is given in Fig 6 18 where the shielding box the connectors the detector biasing and the test networks are also indicated 127 Chapter 6 24 DETECTUR BIAS DETECTOR INPUT AMPLIFIER POLE ZERO ADJUST NETWORK ISOLATING UUTPUT CAPACITOR TEST CAPACIT TEST INPUT Fig 6 18 Charge sensitive preamplifier The basic blocks are the charge sensitive loop the pole zero adjustment network and the output amplifier The charge sensitive loop determines to a major extent the noise performance of the preamplifier The fundamental concepts about these blocks can be found in the document IAEA TECDOC 363 SELECTED TOPICS IN NUCLEAR ELECTRONICS pages 72 through 77 and in the document IAEA TECDOC 309 NUCLEAR ELECTRONICS LABORATORY MANUAL pages 77 through 83 The drawing of Fig 6 16 also shows inside the shielding box the detector bias network consisting of RICB low pass filter and decoupling resistor RB the isolating capacitor Ci and the test network consisting of terminating resistor Ro and injection capacitance Cinj If vou have such a type of preamplifier to troubleshoot check first whether or not the output lies within its linear range without even opening the PA box For such a purpose connect the PA output to a scope put
69. from 24V up to 10 If 94 Chapter 5 17 9 1791 3 3 500151533 039919 34v 03 xHv 5404 722 946 M e i Jay 542151530 ZEA E e A lt Pid ino AOS 143 1 x02 Of FOV 39V110 HOH lt 0 NGL ug 295 cD IPPONI 20 90 J NI 3HV 530112v4v2 an 9 x1 3uv 50151 34 gt 39 sees 1559 21 SS e 3 A NO rana 9 as 92 031312395 3S1M49H10 5531 SQ ION ssocarw Qs v2 22 r Zig 2 15959 70 OC LHS 3123 091 6a 8s eT SIPNI 10 ie JOVLIOA v8422N 1 660 ag r 97 mae 1 39 5 4n 0 O2 03 iu HV bias supply ORTEC Model 459 95 Chapter 5 18 this is mot observed remove the load by unsoldering capacitor Cl3 Check aga n If there is no voltage at the output check the current limiting circuitry which consists of zener diode D3 and trans stor Q9 it works like a shutdown device by driving the transistor 010 into saturation When everything seems normal check with the oscilloscope the waveform of the signal which appears at collector of transistors Q5 Q6 If there is no rectangular pulse visible the amplitude of the pulse should be dependent on the emitter voltage of transistor Q7 check transistors Q3 to Q6 or measure with an ohmmeter if the transformer winding has
70. given resistor Therefore you must check that either this voltage is generated by the current limitation or by the voltage regulation Due to the condition that no excessive current load should be there the voltage regulation should be dominant If this is not the case the fault must be in the current limiting circuit For the current limiting transistor the following rule is valid the base must be more positive than the emitter If it is not you must find out how to detect the defective component If any component was changed a readjustment has to be made 86 9 Chapter 5 lt BI BDBBBE 4 a al OU mors ss sss SECIPIEN j fewer sway Commer 7 1 1 t tmesis C 4 21212 j amp vec Cum ITT o a lt Fig 5 3 NIM module power supply of the type 4001M EG amp G 87 Chapter 5 10 5 4 PLUG IN NIM POWER SUPPLY As already mentioned there are NIM plug in power supply modules available to supply NIM bin Such a supply module is described below and shown in Fig 5 3 This module has some limitations it is available only for 12 1 24V 0 5A 12 1 24V 0 5A4 its maximum power capability is 48W at 50C NOTE DO NOT plug in such a module in a NIM crate that already has a power supply in the back
71. in a car with closed windows The mechanical construction might survive high accelerations but this should be avoided if possible The high voltage DC DC converters are vulnerable to moisture try to store the instruments in dry areas when not use If silica gel cartridges are in the instrument their condition should be checked with a periodicity based on observations 264 25 Chapter 11 11 1 7 3 Log keeping Keep a log book and introduce all findings and activities repair battery replacement calibration etc into it Evaluate the entries yearly and try to improve your work by making use of the observations 11 1 8 Instrument Select on Parts Replacement Try to standardize the survey meters reduce the brands The fewer types the easier it is to organize the spare supplies and the repair Check the high voltage DC DC converter transformers if they are not the hermetically sealed type order one replacement and for each ten units one more additionally If you have good workshop facilities you might try to make the transformer If you do not have data on the number of turns measure the weight of the coils and the diameter of the wire from these two pieces of information one can estimate the turn ratios The insulation is about 10 of the available area and the copper could not be more than 40 there If you have to replace a diode in the voltage multiplier and you do not have the same type it is better to re
72. it has bean previously mentioned the ADC board presents the height of the input pulse in the binary code This binary number is the address of the memory cell RAM residing at the CPU board in which the content should be incremented by 1 9 12 1 Collect Part This addition is performed on the miscellaneous board within the part schematically given in sheet 4 and 5 See Fig 9 35 for the block d agram Buffered lines BADO to BAD sheet 4 are seen DDO to DD at A side of the bidirectional buffer A81 74LS245 Data flow direction is determined by signal at pin 1 A81 When data is present indicated by DATA V2 sheet 5 it s latched into A37 an 8 bit latch 74LS273 Outputs of A37 are connected to A inputs of 8 bit summer A25 A38 two 74LS283 connected serially In the PHA PHA line pin 2 A47 high mode the addition of I is achieved by applying high state to the carry input pin 7 A38 from flip flop A7 while B inputs are grounded The number of counts for each channel are contained in three bytes See APPENDIX for details A46 A50 448 452 DMA ADC sheet 4 MISC sneet 4 MISC sheet 5 Fig 9 35 Collect part of the Miscellaneous Board 204 33 Chapter 9 In the first step 1 is added to BYTE 1 The result is put in the flip flop A7 The modified BYTE 1 is returned to the same memory cell through demultiplexers A50 A52 sheet 4 and the bidirectional buffer A81 Next BYT
73. it is best to use charts to show the status of the seven pins For example use NEG for negative POS for positive Inactive pins that illuminate neither LED should not be left blank otherwise you may not know if you have already tested the pin Instead use an X to represent any undefined logic state Beside each number is the abbreviation of its name as well as an O for output and I for input When the connector is charted you ll have a good idea of what control logic is being used Two examples one for a DTE and one for a DCE are given DTE DCE Pin 1 0 Volts Pin 1 0 Volts 2 TD 2 X 3 RD I X 3 RD 0 NEG 4 RTS 0 POS 4 RTS I X 5 CTS I X 5 CTS POS 6 DSR I X 6 DSR X 8 DCD I X 8 DCD 0 X 20 DTR 0 POS 20 DTR I X The important factor is that all requirements of the ports with regard to pins being on or off must be met 216 7 Chapter 10 You easily test how the control inputs are working If you apply a negative voltage 3V to DSR pin 6 of the DTE you disable it The cable between the devices to be connected is important for successful implementation However after a cable has been built or supplied a number of other items must be compared and set properly before the interfacing will be complete Following you will find a checklist for options generally found on computers and peripherals Item Options Speed 75 bps to 19 200 bps Flow control ETX ACK XON XOFF Hardware Parit
74. must be used for load and measurement to avoid any voltage drop error For removal of the chassis from the bin the two screws on the left and right side of chassis behind the bin have to be removed 5 3 3 Troubleshooting When dealing with a nonfunctional NIM power supply the first step is to measure all output voltages If one or some output voltages are missing measure the corresponding unregulated DC voltage If all unregulated voltages are there check if there is an excessive load current by measuring the voltage drop across the current sense resistor corresponding to the missing output voltage If until now everything seems normal measure the voltages of the following pins at the corresponding regulator IC Compare these values with the theoretical ones 85 Chapter 5 8 Pin 7 8 V depends on supply Pin 5 common for positive voltages or negative supply line Pin 4 must always be 6 9V higher than pin 5 No discrepancy found check that the current limiting transistor is fully cut off any one of the transistors Tl 2 T5 T7 T9 In normal conditions the base must always be more positive than the emitter If a fault is revealed measure the DC voltages in the circuit around this point Here you can already obtain the information of what could be the cause of the fault If everything is normal measure pin 6 of regulator IC The following considerations are valid for the positive supply lines the output vol
75. occurred If a curve tracer is not available in your laboratory you can construct the very simple transistor tester of Fig 6 8 The tester accepts on two different sockets both NPN and PNP transistor The two position two pole switch selects either type The tester is basically a B meter and is surely much more effective than a simple ohmmeter employed to determine whether either junction is open or not With the tester of Fig 6 8 you put the transistor under test on the relevant socket having previously correctly positioned the switch and take note of the panel meter reading If such a reading is between 0 your transistor has to be replaced DIGITAL PANEL METER Fig 6 8 Simple transistor tester It should be realized that transistor testers are available on the market References PORTABLE TRANSISTOR TESTER MODEL 510 FOR IN CIRCUIT TESTS BK PRECISION They usually can be directly applied to the transistor to be tested without removing it from the printed circuit board If such a fixture is available then you May immediately make clear whether the fault in your circuit depends on the transistor or not If it does you simply replace the transistor and check whether the circuit works or not If it does not work then in any case you must disconnect the transistor and check R3 R4 and R1 R2 116 13 Chapter 6 It has still to be considered how to proceed if the VB voltage turns out to be wrong after
76. of channels is also kept within the miscellaneous board under the name range See Table 9 7 for the coding The range code is used by the limit logic on sheet 4 A44 55 A56 and A57 to prevent the ADC from generating an address larger than the memory assigned to it Where to find and how to use the base address and the range code Miscellaneous board sheet 4 contains its own status register You can find latches A47 A49 and 51 74LS273 74LS174 7415273 providing 22 bit data storage The last 8 bit latch 7415273 also controlled by the miscellaneous board is moved into the ADC board sheet 4 A35 The lowest 5 bits are the base address while the three highest bits represent range code RO Rl R2 In A47 49 and A51 information is stored about the current operating mode PHA MCS and other system variables This information can be sent to DDO to DD7 lines through the three state multiplexers 74LS257 A46 A47 A48 A50 Such configuration is called I O port in the computer language Data are written into output latches with signals delivered at outputs of A62 two to four line decoder and activated by the 8085 OUT command pin 5 A63 Data from ports are read when the 8085 IN signal is given pin 9 A63 The port addresses are transmitted through lines BA9 BA12 BA13 BA14 BAIS Output lines PO3 output and PI3 input control the port in ADC 207 Chapter 9 36 APPENDIX 1 To count up to 220 c
77. off high voltage cover the detector with a tight plastic cap and remove the detector with cryostat from the dewar If you are fast the detector crystal itself can be saved and the costs of repair will be only for mounting a new Be window Without vacuum but with high voltage on the detector will heat up the Li will drift out of the detector and you will have to buy a new one If the detector is properly cooled and yet there is signal at the preamplifier output there are several possible reasons you forgot to put a calibration source in front of the detector the high voltage is not provided check the operation of the bias supply and the connections the low voltage power supply usually 24 V is not in order check the outputs of the preamplifier connector mounted on the main amplifier backplane and the connecting leads the preamplifier is defective closely inspect the printed board in the preamplifier and all connections 13 Chapter 12 the inaccessible parts of the detector the crystal itself or cooled FET are faulty in this case without a well equipped vacuum laboratory you can do very little iv The detector resolution has deteriorated The most frequent reason is the humidity and the condensed water in the preamplifier Use a hairdryer to remove moisture A second possible cause is dirt on some components of the preamplifier or on the connector pins protruding from the cooled pa
78. on the Rl R2 voltage divider on T3 that fall under the discussion developed for the circuit of F g 6 2 one has to consider now the problems related to a short circuit on C or R3 The relevant symptoms are VE E2 a VB E2 7V Fig 6 4 Common emitter transistor stage If these symptoms appear disconnect C on one side and measure VE and VBE again If the hypothesis of C is confirmed the sense that with C disconnected 2 E2RI VE VB 0 7V Rl R2 replace C with C disconnected the fault does not disappear you have to suspect that R3 is short circuited therefore replace it ATTENTION Some of the short circuit open circuit situations may not necessarily be due to a defective component but could be simulated by a stray jumper or an ill soldered terminal in the layout Therefore prior to proceeding to disconnect a suspected component visually inspect the concerned part of your circuit Replacement of a defective transistor cannot always be done with the same type of device This is especially true if the instrument under repair is of old design and the components to be replaced are obsolete It may sometimes happen that the specimen used for replacement actually has better gain bandwidth properties in which case the new transistor may exhibit high frequency oscillations Sometimes the frequency of these spurious oscillations is so high that you cannot detect it unless a sa
79. or changing the scale of the pulse generator and observe the output of A5 It should move with a time constant of either 1 5s or 3s according to the selected range Trouble can also come from the circuitry associated with the detection of overrange Whenever the capacity of the 6 bit counter is exceeded flip flop All is set by a signal coming from monostable Al2b the output of the flip flop sets the 2 bit counter A9 and parallel loads A8 to 0101 the content of the 6 bit counter is 110101 This is simultaneously transferred to latches A6 and A7 and added to apply 1101010 to the DAC the LSB of tne DAC is grounded and the meter will be deflected almost fuil scale until reset occurs 5 seconds later A failure of the overflow flip flop All may have various consequences because of its many connections for example if pin i of All stays at logic O which is the state after overflow counters A8 and A9 would be unable to count All is reset by a signal from monostable AlJ7b 164 S91 e d uua nt FEE Chr ene Pr as L hd 47 4 Dy a u 4414355 Iste uU Ie h 2 wares lt Quar MACOS Coma dC Ln SAME AMI CAA wagte owt MIA IJ aun 4F 4 UA gt 7 mm 4 EEE ALK VOVE At FMS ON Fang MNA emerat ACI SIDES C Ok 4 N NIKA 90 0065 ALE sabre amp ZY MES 2424 ows feo NL EUS MIN R 426 6 v ICT af
80. outside one should give the necessary voltage after the original supply was disconnected from the detector From a pulse generator detector signals can be simulated to drive further circuit sections 11 1 4 6 Identification of key points if circuit diagram is not available It is easy to find the battery connectors this is the first key point for testing For the second key point one should search near the transformer The third test po nt could be located by searching for a filter capacitor with a few hundred volts rating The fourth test point should be near the signal entry one should search for active components outputs One may save much time during future repairs if all identified points are documented even if only a rough sketch It is important to save such documents and to make note n the instruments log book that such drawing already exists 249 Chapter 11 10 11 1 4 7 Expected normal voltages currents and pulse shapes at key points On the first test point the voltage should correspond to the number of cells in the unit If the batteries are new and their short circuit current is over 1 amper there should be not more than 104 drop if the instrument is switched on Higher current uptake is often the sign of non functioning DC DC converter At the second test point a periodical signal should be present the amplitude depends on the type of the converter The third test point is the DC output of the conve
81. signal on the input deteriorated resolution either damaged detector or moisture accumulation in the preamplifier bad efficiency x ray dirty Be window or detector crystal surface Chapter 12 12 There are some actions that you can implement to repair defective or improperly operating detector But there are a number of faults when the detector must be returned to the factory for repair i ii iii 290 ATTENTION Do not apply high voltage to a detector which Let us analyze some typical cases When touching the detector cap it feels very cold moisture or ice accumulate at the point closest to the dewar This is a sure sign that the vacuum inside the detector cryostat is bad If you have a good vacuum laboratory with a pumping system and a He leak detector you can find the leaking spot and repair it Then you pump the cryostat for several hours at the same time heating the bottom part of the cryostat and the protruding dipstick to 80 or 100 degrees C Without the proper vacuum equipment the detector should be returned to the manufacturer s service laboratory shows signs of a bad vacuum inside the cryostat Some detectors but not all have a temperature sensitive switch inside the cryostst that prevents the application of high voltage to a detector that is not sufficiently cooled The most obvious loss of vacuum happens if the Be window on an x ray detector breaks Immediately switch
82. step wise motion is under the control of a preset counter programmed by the step length switch In manual mode all rotation direction orders are controlled by the manual switches and the motors move only while they are pushed and only the safety logic can inhibit them All repair activities should start with the checking of the safety switches because if they are shorted the mechanical system will not stop on the borders and if the torque limiters are bad expensive damages can be expected For this reason it is a good practice to put the detector into the center of the scanning area during the initial part of the testing If triacs should be replaced the rule is to change them in pairs Use fuses to protect them during first trials after replacement 11 2 4 9 Alignment of the mechanical system The detectors are rather heavy and the mechanical system can operate properly only if the beam supporting the heavy lead shield is accurately leveled The mechanical system wears out quickly without this precaution It is important to check the leveling of the scanner after transportation 11 2 5 Quality Control of the Repaired Instrument Recommendations of the IAEA TECDOC 317 on Quality Control of Nuclear Medical Instruments should be followed 11 2 6 Preventive Maintenance Recommendations given to the Nuclear Medical Pilot Laboratories should be followed that is instruments should be protected from environmental effects like d
83. the LM319 5V The protection circuit should be checked if the input analog signal fails to appear at the comparator The analog signal is applied at the inverting terminal of the timing comparator All through emitter follower Q13 016 works as a lOmA current source The circuit up to the All inputs when the crossover mode is selected is shown in Fig 7 3 Note that this mode of operation may be selected only if the input signal is bipolar Fig 7 3 Timing discriminator input circuit in crossover mode In this mode of operation the input analog signal and the comparison voltage level are both derived from the emitter of Q13 the comparison level is obtained by filtering the signal out with capacitor C18 Thus the comparison voltage follows eventual slow fluctuations of the analog input baseline voltage as may be verified by applying a dc voltage at the input Note that the lmA current sink Q20 allows the differential de level at the All inputs to be varied by 100mV through adjustment of 10 this 15 easily checked with a multimeter if no input signals are present This adjustment is intended to minimize the time walk this parameter is discussed in detail in IAEA TECDOC 363 148 5 Chapter 7 The working condition of the comparators is easily checked In the absence of input pulses the output of the baseline discriminator pin 7 of A6 should be at logic l and the output of the channel discriminator should be at logic
84. the detectors with the windows on the photopeak of the radioactive isotope which was introduced into the body for investigation Counting rate meters are driving the display system which moves together with the detector above the scintigram paper The measured counting rate drives the intensity to colour information converter consisting of a multi coloured typewriter ribbon positioned a servo system under an electromagnet controlled hammer called the tapper In multi detector systems each detector has a separate display unit As the measured intensity changes various coloured portions of the tape will be put under the tapper by the servo Since the detector and the tapper move together if the tapper hits on the ribbon the colour mark on the scintigram will correspond to the measured intensity As the detector moves above the selected area of interest it collects the radiation intensity data along its path displayed in colour code with a display determined by the time constant of the counting rate meter The fidelity of the image will be a function of the Statistics If the detected number of pulses per square centimeter are low the related statistical fluctuation will be high so a longer time constant is needed to smooth it out For a good quality image 600 pulse square cm must be obtained therefore the detector speed should be adjusted to meet this requirement The Scanning speed should be fairly stable easily adju
85. the circuit the fault appears Look for cold soldering points Check the fuses Transformers are frequently damaged by an overload fuses of the wrong value were inserted and did not protect the circuits The rectifier diodes can get damaged the most frequent reasons are a repetitive peak current and b reversed bias voltage Occasionally we might find that the designer made a wrong selection of the diodes the assumed specifications do not correspond with the ratings Typical examples are with the frequency of the mains 50 60Hz or voltage 117 220V In older equipment capacitors may become defective due to heat they are used at the limits of their voltage specifications this is especially true for tantalium drop form capacitors Pass or power transistors are mainly destroyed by overvoltage excessive 79 Chapter 5 2 current overheating Defects in regulators are caused by reversed bias and overvoltage voltage spikes which are exceeding the maximum rating Sense resistors may be destroyed by excessive output current Dust and dirt obstructs cooling of components which might lead to overheating and breakdown ATTENTION NEVER trust fully the circuit diagram Compare it with the circuitry and wiring ATTENTION NO normal fuse can protect a semiconductor it is always the other way around NOTE After repair a re adjustment of the instrument has to be made If electronic components were replaced by simil
86. the other end will get indication that the transmission line is available If power is off the other end will not have DSR indicating that the communication path is not established Function PCi Pin DTE PC2 Pin DTE Function PG gt 1 PG Protective Ground SG 7 gt 7 SG Signal Ground TD 2 __ 2 TD Transmit Data RD 3 Be 3 RD Receive Data DSR 6 el 58 6 DSR Data Set Ready DTR 20 pc 20 DTR Data Term nal Ready The other element of the control function on the interface is path control Request To Send RTS pin 4 is normally generated by the DTE For data transmission to be allowed Clear To Send CTS pin 5 must be received by the same DTE So we loop the RTS signal back to the originating DTE by wiring it back to pin 5 CTS Whenever the DTE for example PCl raises RTS it immediately receives a CTS signal indicating that data transmission is possible As for the need of the receiving device to have an indication that data will be arriving we must provide for Data Carrier Detect DCD pin 8 to be derived from the same source RTS Thus we also connect RTS pin 4 at the originating DTE PCL to the Carrier Detect lead pin 8 from receiving device By making these cross connections not only will a CTS signal be given but when RTS is raised the other end will also receive its DCD signal indicating that data transmission is possible Repeat these connections at both DTE s to allow two
87. they must be complementary and change state at every time mark 163 Chapter 8 10 If the above signals are correct check the behaviour of the A8 binary counter and of the A9 dual D flip flop that works as a 2 bit binary counter Observe if the latches and A7 are correctly loaded if this is felt to be difficult observe a bit at a time or keep the rate constant and verify that the two latches have the same contents The working condition of the adder is easily verified NOTE that the connections shown the schematics from latch A6 to the adders Al A2 are wrong 8 5 2 DAC and Averaging Circuit Start by keeping a constant input to the DAC and check the operational amplifiers as discussed elsewhere in this manual Then adjust the input pulse generator in such a way that the lowest seven input lines of the DAC at logical 1 The panel meter should read full scale adjust the offset potentiometer to compensate for small deviations If adjustment cannot be obtained measure the voltage at the output of A4 then reduce the pulse generator rate in a way that only the lowest six input lines of the DAC are at logic l the output voltage of A4 is now approximately one half of the previous value otherwise the DAC is not working properly If it does check the circuit around A5 and the meter To examine the behaviour of the averaging circuit R20 Cl and C2 introduce large step at the DAC input for example by stopping
88. this interface must be explained DTE DATA TERMINAL EQUIPMENT like computers terminals or printers DCE DATA COMMUNICATION EQUIPMENT like modems As one can see from above two different types of devices exist which can be connected together The first case to connect a DTE to a DCE should not create any problem you simply connect them straight through This is because each output pin on a DTE has a corresponding input pin on the DCE Signal flow is shown from the DTE side 212 3 Chapter 10 PC Pin DTE Lead name abbreviation Modem Pin DCE l Protective Ground PG gt 1 2 gt Transmitted Data TD gt 2 3 lt Received Data RD lt 3 amp gt Request to Send RTS gt 4 5 Clear to Send CTS 5 6 Data Set Ready DSR 6 7 Signal Ground SG gt 7 8 Data Carrier Detect DCD lt 8 20 gt Data Terminal Ready gt 20 The second case to connect two devices from the same type namely two DTE s together can bring you into trouble Therefore let s do it step by step The kind of cable we have to use is called a NULL MODEM CABLE GROUND connect them straight through Function PCl Pin DTE PC2 Pin DTE Function PG 1 gt 1 PG Protective Ground SG 7 gt 7 SG Signal Ground
89. this is in the linear range or its output is saturated dc analysis should reveal where the defect is Proceed to remove it and only after de conditions have returned to satisfactory levels switch on the generator again and carry on signal analysis It may easily occur in a misused 136 33 Chapter 6 instrument that more than one gain or shaping stage is faulty rhen proceeding from input towards the output repeat the outlined procedure for all the defective stages As an example of real troubleshooting action a specific amplifier Canberra 2020 which is very frequently used in high resolution spectroscopy systems will be considered This amplifier is composed of several stages see Figs 6 23a 6 23b and 6 23c l Input buffer for impedance matching 2 First differentiation stage 3 First amplifying stage gain 3 10 adjustable by fine gain potentiometer 4 Second amplifying stage gain 30 fixed at the first 3 gain positions amplifier is by passed 94 Third amplifying stage gain 1 10 6 First active integrator stage 7 Polarity amplifier 8 Second active integrator stage After this stage the signal is split along two paths a Second differentiation and buffer amplifier for bipolar output and b Output buffer stage for unipolar output it is reached by either direct feed or via delay line the output driver stage is controlled by the baseline restorer circuitry The amplifying stages 1 2 an
90. voltages 5V 12V 24V 12V 24V This is very convenient because it is already an indication as to where and how to start with troubleshooting If no LED is on and the main fuse Fl101 is not blown the fault may be in the 24V supply line Check the temperature switch if it is closed then measure the reference voltage 1018 Next measure the output of the operational amplifier A3 which should be approximately 15V The base voltage of Q2 compared to ground should be a little higher than 257 If not check the voltage across Q3 If this voltage is less than l 5V it indicates that there is an overload at this output and current limitation is active This is valid for all other output voltages except for the 5V There it is not easy to distinguish between an overload situation and the presence of the activated overvoltage protection Due to the overvoltage protection the thyristor Q19 is fired and shorts the output to ground As long as the current limitation works properly there is only one way to reset the current limitation by switching the instrument off and on again after removing the load Only in this way is it possible to determine whether current limitation or overvoltage causes the action If you suspect that the overvoltage protection has become active you should switch off the instruments and connect it via a VARIAC to the mains as shown in Fig 5 5 Increase slowly the voltage to the instrument In this way it
91. way transmission Function PCl Pin DTE PC2 Pin DTE Function PG l 1 PG Protective Ground SG 7 gt 7 SG Signal Ground TD 2 o m 2 TD Transmit Data RD gt 3 RD Receive Data DSR 6 lt __ 7 6 DSR Data Set Ready DTR 20 peg 20 DTR Data Terminal Ready RTS 4 4 RTS Request To Send CTS 5 ee 5 CTS Clear To Send DCD 8 7 CA 8 DCD Data Carrier Detect 214 5 Chapter 10 The path control requirements have been met in the null modem cable As we have mentioned above two different types of devices DTE and DCE are existing so we have to ASCERTAIN THE SEX OF THE EQUIPMENT before we can connect them together The best way to determine whether an equipment using RS 232 ports is configured to emulate DTE or DCE provided signals is to review the device documents Consult the user s manual for this information If documentation is not available a break out box may be used to determine which leads are provided by a device For specifications of a break out box see Chapter 3 Section 3 2 17 Connect the break out box to the RS 232 port and make sure that the device is powered and the port in question is active or enabled The LED s on the box should display which leads are being generated from the device From this display a determination can generally be made as to whether the device is emulating DCE or DTE green LED s indicate negative voltage red LED s indicate positive vol
92. 1 15 Scanner controls 268 29 Chapter 1l The activity to colour servo should follow the movement of the display meter as the source is moved under the detector The next test is concerned with the X Y movements of the detector First the LIMIT or LIMIT SWITCHes should be set for a short few centimeter long line length with full size step wise motion and the scanning should be started with the START switch in the lowest SPEED range The scanner should start meandering within the preset borders The speed should be adjusted for higher and higher speeds up to the maximum Take care because if the limit switch is bad the detector might try to run away breaking parts of the mechanical system this is why the border control checking is recommended on the lowest speed range If the system is already moving a small source a so called phantom organ should be put under the detector and imaging should be attempted Here one should follow the recommended setting up procedure described in the manual First position the detector above the source and adjust the CALIBRATION control to get the display meter pointer to reach the red colour zone representing the highest activity zone on the scintigram The speed should be set to get the recommended 600 counts square centimeter information density An image of the source should result from this activity similar to those which were taken previously under reference conditions The detect
93. 15 110320 110325 110274 590162 590174 590182 590200 590250 530661 610300 610324 610308 610352 490304 490308 490314 740316 740324 68E223 68E225 68E227 68E229 67E853 67E854 67E855 67 856 67 860 209712 2757700 2758300 2754700 2754850 59 Chapter 3 40 71 100 Bipolar Transistor 2N3904 72 100 2N3906 73 20 Transistor BFY90 74 10 Comparator LM710 75 10 LM711 76 10 LM311D 77 10 Operational amplifier LM741CD 78 10 LM748CD 79 10 LM318D 80 10 LM324D 81 10 LF356N 82 10 LF357N 83 10 TLO71CP 84 10 CA3140E 85 20 Voltage regulators LM723CD 86 10 UA7805CKC 87 10 UA7812CKC 88 10 UA7824CKC 89 10 UA7905CKC 90 10 UA7912CKC 91 10 UA7924CKC 92 20 LM317T 93 20 LM337T 94 10 LM340K12 95 10 Darlington Transistor BD651 96 10 BD652 97 5 Power Transistor 2N3055S 98 5 Power switching Tr MJE3055 99 5 Power HV Transistor BU208 100 5 Power switching MOS FET BUZ80 101 5 Power Transistor 102 20 npn Transistor 2N2219A 103 20 pnp Transistor 2N2905A 104 20 npn Transistor 2N2222A 105 20 pnp Transistor 2N2907A 106 10 npn Transistor BD139 16 107 10 pnp Transistor BD140 16 108 5 Thyristor 2N4441 Diodes zener diodes 109 50 Diode 1N4007 110 100 1N4148 111 20 1N5408 112 5 Bridge rectifier 3A 600V 113 3 10A 500V 114 5 Switching diode MR854 115 10 Zener diode ZPD 5 1 60 2755200 2755300 1754000 4185300 4155350 4152290 4155380 4155405 4182575 4153175 4059000 4059060 495
94. 3 3 9 DC Power Suppl 32 A large number of different types are available on the market covering the range from rather simple ones to high performance power supplies Typical specifications for an application in a nuclear electronics laboratory are 3 independent outputs 0 5 5 V 7A 0 30 V lA 0 30 65 V 1 2 0 6 A Output voltage adjustable with precision pot 0 3 Output current adjustable short circuit proof Load effect 0 100 lt 5 lt 8 mV Source effect 10 lt 2 mV Noise 5 mVpp Over voltage protection ABC 52 33 Chapter 3 3 3 14 Digital Logic Probe Compatible with DTL TTL CMOS Min pulse width lOnsec supply voltages 4 5V to 30V dc indications HI red LO green open circuit yellow pulse memory red mode DELUXE MOLDED PLASTIC CARRYING CASE pulse memory level TTL CMOS frequency range GROUND LEAD dc 50 MHz input impedance gt 10 M IC CLIP LEAD General specifications LOGIC THRESHOLD TTL Logic 1 HI 2 2V 0 3V 5V DC CMOS Logic l HI 70 VDD 10 VDD Logic O LO 0 7V 0 3V 5V DC Logic O LO 30 VDD 10 VDD Power 4 5 to 30V DC 50mA max 5V DC Input Overload Protection 50V DC AC continuous Max 120V DC AC for 10 seconds Power Input Protection 50V DC AC continuous Max 100V DC AC peak for 10 seconds Audible Warning Built in buzzer emits alarm when an input signal exceeds the VDD of the circuit being tested or when
95. 5500 4052950 4155370 5051450 5051600 5051750 5051800 5051950 5052100 4152550 4153600 4153750 1456150 1456200 2752500 2454900 1952950 1956800 2552875 2781100 2781950 2781250 2782150 1355300 1355500 2787800 2688100 2658150 2688876 55A658 57A190 2454910 2558000 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 adiu Servicesortiment Precise fuse Soldering supplies 5 5 5 Connectors WWW W 300 25m 10m 20m 10m ZPD 5 6 ZPD 6 8 ZPD 8 2 ZPD 10 ZPD 12 ZPD 15 ZPD 24 ZPD 33 fast slow slow FLUITIN soldering wire Desoldering wire and cables BNC extension connector BNC T BNC cable plug NIM connector male NIM connector Centering pin Centering recept Contact pins Contact receptor Protecting cover Connector 9pol 25pol 9pol 25pol Pins Pins Cable RG58C U RG59B U Cable 5pol Flat cable 50po emale ors s male male female female 1 1 3mm 2 5mm 0 1A 0 4 1 6 4 0 4A 1 6A 4A 100g 0 75mm Chapter 3 2588050 2558150 2558250 2558350 2558450 2588550 2558800 2588950 466240 466244 466268 466274 466280 466284 466319 466325 466329 111 402 106752 101 756 78 270 78 290 78200 55 7251 55F7253 5
96. 5F760 55F766 55F7725 55F778 55F798 55F400 55F401 55F410 552412 552408 552418 96 730 96 746 942306 942439 61 Chapter 3 42 Digital integrated circuits 156 50 SN74LSOON 4352750 157 50 SN74LS02N 4352900 158 50 SN74LS10N 4383250 159 50 SN74LS74AN 4354600 160 50 SN74LS90N 4354950 161 20 SN74LS138N 4385900 162 20 SN74LS123N 4385550 163 20 SN74LS191N 4387150 164 20 SN74LS193N 4387250 165 10 SN74LS374N 4359900 166 10 SN74LS245N 4387800 LEDs 167 20 LED 3mm red 6784350 l68 20 3mm green 6784450 169 20 5mm red 6754500 170 20 5mm green 6754600 Switches 171 5 Switch lpol E E 10G700 172 5 2pol E E 10G740 173 5 2pol E A E 10G750 Miscellaneous 174 1 set Screws 16H695 175 1 set Nuts 16H954 176 1 Heat conducting paste 80B533 177 1 pak Wire wrap pins 12H592 178 2 Fuse holder 5x20mm 466628 179 2 6 3x31 7mm 466642 180 10 IC breakable sockets 16B110 62 43 Chapter 3 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX SKILLS Reading and Understanding of Circuit Diagrams Diagrams are the main aids to repair For fault location the most essential information is that concerning functional structure i e how the components are connected to perform their required function Circuit diagrams are often criticized the basis of bad presentation due to this national standards were developed to specify the requirements for an efficient diagram According to British Standard Diagrams sh
97. ALK ADORESS AND SERIAL showed POLL MODE LATCHES RSET RESET ACTIVE AT POWER ON OR DURING REN Ourpuss RESETS ALL HANDSHAKE CIRCUITS ANO MA MY ADORESS ACTIVE FOR D 08 5 S20 t S20 5 THE REMOTE LATCH If TON SELECTEO MONITORS REN TO PREVENT BUS CON 6 Mode Latch FLICT WITH AN ACTIVE CONTROLLER moun OY 07 DATA17 BUS GENERATED 42 femal Clock Oval DATA VALID FROM ACCEPTOR HANDSHAKE TIMING THE CLOCK CIRCUIT GENERATES THE TIMING FOR PROPER OPERATION OF ABAT ABORT FROM Ht SET CIRCUIT INTERNAL AND EXTERNAL CIRCUIT REQUIREMENTS Outputs Posave interval GREATER THAN 3 esc Sf SERIAL POLL ACTIVE AFTER SPE COMMAND Negatwe interval GREATER THAN 1 sec MODE FROM THE BUS 0702 001100 AND O 01 INACTIVE AFTER SPO COMMAND 07 D 001100 AND 01 0 7 Service Request Logic inputs FEM REMOTE FROM REMOTE LATCH SPM SERIAL POLL FROM SERIAL POLL MOO LATOH MOO TE TALK ENABLE FROM TALK DELAY GENERATOR ECO ENO OF COLLECT FROM COUNTER BOARD FOR ANY STOP COLLECT Chapter 10 22 4 If everything was correct disconnect all devices and try it with a single one Jo If you don t have success try another cable another unit 6 If after all these tests your controller still does not work open it and check if the board is installed properly Ves Measure the supply voltage of the board 8 Take an oscilloscope and check the signals TTL level 9 If no signals after the GPIB transceivers appear check if Signals ap
98. ALUES 10k Fig 6 16 Operational amplifier with a gain of 10 Consider now the following amplifier whose nominal gain should be 10 but actually is found to be 1 Fig 6 17 The fault may depend on open circuited or R2 short circuited Open and short circuit may be related to faults on the printed circuit board In this case visual inspection aiming at detecting possible interruptions accidentally disconnected components stray jumpers has to be carried out first If nothing comes out of this inspection measure the resistors Rl and R2 and change the defective one s Remember that there is still the possibility of a gain in the operational amplifier much below the nominal value in which case it has to be replaced 126 2232 Chapter 6 10nF NND DUTPUT Fig 6 17 AC connected operational amplifier with a gain of 10 6 2 TROUBLESHOOTING OF SPECIFIC EQUIPMENT 6 2 1 Troubleshooting of a Charge Sensitive Preamplifier Existing commercial charge sensitive preamplifiers fall into four categories with input FET i Resistive feedback preamplifiers operating at room temperature ii Resistive feedback preamplifiers with input FET cooled with input FET iii Optical feedback preamplifiers operating at room temperature iv Optical feedback preamplifiers with input FET cooled Each category requires specific troubleshooting procedures As an example a preamplifier with resistive
99. After the above mentioned procedure an output signal of the right shape should be visible at the unipolar as well as at the bipolar output Now switch on the baseline restorer and compare the signal with the previous one If its positive going lobe is left unchanged and only the recovery towards the baseline is affected you can assume that the BLR is working Connect the oscilloscope to the output feed a pulse to the amplifier and change the gain reducing the amplitude of the test pulse In this way the various feedback loops are checked The next step is to check by setting the several shaping time constants that the output amplitude varies only over a small range If there is a big change in amplitude you can assume that either the switch gives a bad contact or one of the RC networks are defective The pile up rejector cannot be checked with a normal pulse generator There are two types of pile up trailing edge pile up and leading edge pile up A test is possible with a short double pulse fed into a RC network time constant about 50 usec To compare the signals with the manual the scope must be triggered by the first pulse Fig 6 24 indicates the pulse forming network The settings of the double pulse generator without load should be the following amplitude 5V pulse width lusec repetition frequency lkHz double pulse selection pulse delay variable from 3usec up to 100 N Check the sev
100. C ABC ABC BC ABC ABC ABC ABC ABC ABC ABC ABC ABC BC BC ABC ABC ABC ABC BC ABC ABC ABC BC ABC ABC mou uou n rz oup o List of tools materials cont d 3 1 Tapes 3 1 46 Saws 3 1 47 Saws special 3 1 48 Tool bags 3 1 49 Tool kits 3 1 50 Storage boxes 3 1 51 Cable crimping tools 3 1 52 Wrapping tools 3 1 53 Blower and vacuum cleaner 3 1 54 Screw punches 3 1 55 Tools for surface mounted devices 3 1 56 3 1 57 Glue instant action type like Loctite or similar 3 1 58 Winding machine small size with turn counter Detailed descriptions of the most presented in the following pages ABC ABC BC BC ABC ABC important Chapter 3 tools are 23 Chapt 3 1 1 b 24 er 3 4 Room For construction the following should be considered Size big enough not only for the work bench but also to allow space for tools test instruments spare parts components documentation faulty instruments up to rack size and detector with crystal assemblies repaired instruments trolleys separate storeroom dirty room e s separate clean room documentation room Lighting system preferably daylight with blinds for screenwork and daylight fluorescent lamp Floor surface without cracks or chinks Material sealed and painted concrete PVC
101. Checking a Faulty Transistor The following simple rules will help you understand whether or not a trans stor is faulty Assume that the transistor of Fig 6 1 is expected to be ON All transistors in the amplifying part of an analog instrument should actually be ON Determine the currents through R1 and R2 by measuring the voltage across Rl and R2 and applying Ohm s Law and the VBE voltage of Tl If IC IE and VBE lies in the range 600 700 mV for a silicon transistor or 300 500 mV for a germanium transistor then Tl works properly 107 Chapter 6 If Rl is not present but there is a resistance in series with the base of Tl like in Fig 6 2 then determine the currents through R3 and R2 and the V BE voltage If VBE lies in the same range as before and is 10 to 100 times or more lower than then again Tl works properly Fig 6 1 Basic transistor Fig 6 2 Transistor stage stage with base resistor The transistor has to be replaced if a 108 t While VBE falls into the correct range IC is much smaller than IE Fig 6 1 or IB is nearly equal to IE Fig 6 2 These symptoms are typical for a transistor where the base to collector junction is OPEN VBE exceeds 1V This happens when the emitter to base junction is OPEN VBE is not within the correct range and VCE is almost zero This happens when the base has been punched through or collector and emitter short circu
102. E AWS al WRN LIORA caw a am T ne 159v NV SF CARTE CONVERTISSEUR Q20t 8Cw 09A R125 sm D R202 Wins 0202 8CW 0A ze adeug Chapter 11 18 If there are no output signals the detector should be disconnected from C211 at point and a signal from a pulse generator should be injected to test the circuit If the amplifiers are good the photo multipliers dynode resistor chain should be tested for continuity preferably with the high voltage on and by stepping from dynode to dynode In some versions the photo multiplier is not in a light tight case after the cover of the probe jis removed Under such conditions the photo multiplier should be removed from its socket before the resistor chain testing otherwise the photo cathode might be seriously damaged For further instructions please look at the section on Detectors in this manual vii The ratemeter and the alarm circuit These parts of the circuit are shown in Fig 11 12 The signals from the probes are first passed into a Schmidt trigger 2100 to remove the effects of the cable Both the signals from the Geiger Mueller tube and the Scintillation detector are standardized to equal length and amplitude in the probes so the counting rate meter is a simple integrator 2101 with varying time constants in the feedback loop in various ranges R104 C106 R105 C107 106 108 R107 C109 output signal of
103. E 2 is inserted and the procedure is repeated Then BYTE 3 is treated However only four LSB are a part of the number represented by BYTE 1 BYTE 2 and BYTE 3 Therefore by applying BYTE 3 signal to the gate Al2 and A24 the sumation is limited to four LSB only during the processing of BYTE 1 or BYTE 2 carry 15 not produced further sumation is meaningless and is stopped When the DMA cycle is over HOLD command is removed and 8085 is returned to the normal operation through line RST 5 5 All commands controlling the data flow and the described arithmetic are generated by the circuit containing AIO A5 A7 A8 A12 A24 and A65 situated in sheet 5 left down We have assumed up to now that BYTE 1 BYTE 2 and BYTE 3 are available However for proper selection the adequate address should be given to RAM The position of BYTE 1 BYTE 2 and BYTE 3 within the RAM is given in Fig 9 36 For proper addressing the address line 15 should be 1 all the time when communicating with RAM ROM is addressed by 15 0 A13 14 have to be set according to Table 9 5 TABLE 9 5 15 14 13 12 o AU 1 1 0 0 determined by base address and range BYTE 2 1 0 1 determined by base address and range BYTE 3 1 1 0 determined by base address and range The above mentioned address lines are controlled by flip flops A13 through three state buffer A65 74LS367 sheet 5 Duri
104. EFFECTIVE TROUBLESHOOTING OF ANALOG INSTRUMENTATION Analog instruments basically consist of analog circuits either linear non linear Some logic functions however may also be present Therefore when you open an analog instrument you will see inside discrete components analog integrated circuits like operational amplifiers comparators analog switches and more rarely multipliers and possibly some digital integrated circuits It is important to point out that even in the most modern analog instruments there are some parts that must be mandatorily implemented in discrete form for integrated technology s still unable to provide the level of performance required for some functions So typically low noise sections in preamplifiers and amplifiers are still built in discrete hybrid form The same applies to some high speed amplifying circuits The sections implemented in discrete form are usually the more important sources of failure or malfunctioning in analog instruments These sections during the lifetime of the instrument are more prone to suffer partial modifications and incorrect component replacement from the user and are more exposed to adverse environmental conditions Besides evident failures and easy to appreciate kinds of malfunctioning analog instruments may present some performance degradations whose detection may imply application of sophisticated tests The last point represents the peculiar difference
105. EM n eset EM Bm Y TALK ADDRESS LATCH 322 2 2 LE M vv j sa esr MEE om ID 24 SIG CND 23 GND 22 21 GND GND 191 GND 18 GND 17 REN 1610108 1510107 1410106 8 NDRC TINRED 6 DAV 51 310103 210102 110101 GPIB CONNECTOR 61 4 059 lt i arn D an 1 aa 3 ats 2 one M d eee au as req AB Cosas cR GME lt TRA iC HR 615 Circuit diagram of GPIB inter facing for Canberra counter 2071 3 3deu5 TABLE 10 3 The following interface schematic twelve functions are described GPIB option functional description in terms of identifiable Chapter 10 on the GPIB the function inputs and outputs with brief descriptions of the output functions 11 Acceptor handshake tering inputs RSET RESET DATA VALID ATTENTION Outputs RED READY FOR DATA oac DATA ACCEPT DvAL DATA VALID 21 Source Nendahake tering outs CLOCK RSET RESET Oac DATA ACCEPT RFO READY FOR DATA Y TALK ENABLE TALK ENABLE OELAY 53 3 Output Byc BYTE CLOCK ROY READY TAKE HAVE IT ACL READ CLOCK 3i Tos Delay Generator moun
106. Generator The direct memory access DMA is used to keep the CRT display refreshed and updated with real time data collection and text This is done once per each Monitor vertical line during the flyback DMA logic generates write and read commands and asks the 8085 to relinquish bus control DMA address generator determines the memory address from which data should be taken The circuit block diagram is given in Fig 9 34 while the corresponding detailed schematic is at sheet 6 and 7 DMA request is sent to the priority encoder sheet 5 residing at the CPU board DMA request signal DCHRI can be checked at TP15 Simultaneously the memory address from which the information should be provided is set at the MUX A81 A63 A98 and A99 output The signal DCHAl confirming that the DMA request has been accepted and executed is returned after 1 us 1 is at TP26 The content of the selected memory location appears on the System bus and the local bus The content is locked in BYTE 1 register Fig 9 28 top left by the BYTE 1 CLK TP29 The next memory address is set and the content from the corresponding memory location is latched in the BYTE 2 register Check TP24 for BYTE 2 CLK 202 zu The action is repeated to get the data BYTE 3 BYTE 3 CLK To run 3 stage ring DATA V1 and CNDMA pin For the character sheet 4 signals CCK TP 5 counter A74 should be revealed loading into A96 A95
107. IAEA TECDOC 426 TROUBLESHOOTING IN NUCLEAR INSTRUMENTS y A TECHNICAL DOCUMENT ISSUED BY THE 89 INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA 1987 TROUBLESHOOTING IN NUCLEAR INSTRUMENTS IAEA VIENNA 1987 IAEA TECDOC 426 Printed by the IAEA in Vienna June 1987 PLEASE BE AWARE THAT ALL OF THE MISSING PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK The IAEA does not normally maintain stocks of reports in this series However microfiche copies of these reports can be obtained from INIS Clearinghouse International Atomic Energy Agency Wagramerstrasse 5 P O Box 100 A 1400 Vienna Austria Orders should be accompanied by prepayment of Austrian Schillings 100 in the form of a cheque or in the form of IAEA microfiche service coupons which may be ordered separately from the INIS Clearinghouse FOREWORD The servicing and repair of nuclear instruments is a difficult task The commercial manufacturers of nuclear equipment can assure reliable service only in the most advanced countries that have many instruments installed In developing countries as a rule good service laboratories organized by the manufacturers do mot exist The nuclear research laboratories must rely upon their own resources to keep the instruments in operation The International Atomic Energy Agency is trying to assist the developing countries by providing different types of service in this field This includes help in the establishment of suitab
108. ON OF THE LABORATORY Chapter 2 2 ORGANIZATION OF THE LABORATORY 2 1 GENERAL REMARKS The contents of this chapter are limited to some general observations and conclusions on the organization and operation of an electronics laboratory that serves nuclear intrumentation and related equipment The same recommendation applies as well for all donated instruments It should be noted that there are several IAEA publications dealing with the topic IAEA TECDOC 309 Nuclear Electronics Laboratory Manual and TECDOC 363 Selected Topics in Nuclear Electronics The optimal set up of a service laboratory depends to a large extent on the social economic and policy situation the country As an example consider the specific regulations in a country referring to the financing and control of material support to the laboratories Therefore it is difficult to present a detailed assessment of the best approach for establishing and operating such a laboratory Below only some points that seem to apply to all countries and situations are summarized 2 2 PHYSICAL ENVIRONMENT A summary of the main items of recommended facilities required for a service laboratory is given here Only a reminder on the essential features to be considered when a laboratory is created are presented Further details are given in the following chapters 1 The laboratory should have a minimal useful area of 10 12 square meters for each employee If Computer Aided E
109. P 25 Pin CI C C20 91 0022 uF x Cr j COH CHT Cool Ciel cis C20 a y 51 27 an 1 l 15 Gata 4 15 Chapter 10 In Table 10 2 are some useful hints for troubleshooting The device which is connected will be in our case a printer TABLE 10 2 Partial list of problems with a Centronics parallel interface Symptom Cause Remedy No data is being Check to be sure power is on printed Ensure the device is in on line mode Check all signals according to the above specifications Computer port driving the printer may not be enabled check the address of the board Refer to PC manual Printer lid if raised may inhibit further printing Printer ribbon may be defective or worn replace it Garbled data Cable could be faulty Timing of STROBE signal incorrect too early or too late Cable too long gt max length 4m Communication line Power may be off on the printer cannot be esta Cable between the devices may be faulty or not blished or main properly wired tained For a detailed printer description refer to the printer manual 10 5 625 IEEE 488 GPIB INTERFACE The general purpose interface bus GPIB is a link or network by which system units communicate with each other It is widely used for automation in measurement and control applications The bus allows the connection of up to 15 dev
110. RENT IN APPLIED oc U QUT C t UNIDIRECTIONAL 1 4 8 AMPLIFIER Fig 9 11 Conversion Fig 9 12 STRETCHER 181 Chapter 9 10 CLOCK Fig 9 13 Simplified ADC 95 3 CHECK AT THE UNITS LEVEL 9 3 1 ADC Board An ADC board contains an amplifier and a ADC As amplifier troubleshooting is not the aim of this chapter explanation will be limited to ADC only See Fig 9 13 for the block diagram In principle you can check the operation of the unit by using only the present instructions However it is strongly recommended also to consult CANBERRA SCHEMATICS SERIES 35 PLUS The ADC board is given in 5 sheets Troubleshooting following the signal path is more difficult than in the previous cases The separate blocks are interconnected with more than one line Thicker lines indicate more than one signal going the same way Arrows indicate the direction of the data flow Tne stretcher for instance accepts input signals and its output is inspected by three blocks stretcher input interrogation logic single channel analyzer and zero crossing discrimination In the case of proper input well defined output signals are also expected assuming normal block operation However in the absence of the adequate control signals on lines DUMP STRET OFF and RAMP ON even a good block cannot work All three control signals are coming from the CONTROL LOGIC block This block makes its decisions by evaluating 14 input s
111. RESPONSE SPM SERIAL POLL MOOE BYC BYTE CLOCK ROY READY ACYL RECYCLE CRAFF ASCII CR ORFF 158 LEAST SIGNIF ICANT BYTE A 8 and Bnot BCD BINARY Bco CODED OGITS ecos Outputs 3 STATE 3 S4 STATE 4 ss STATES Le LAST BYTE END OR IDENTIFY sts RESTARTS 9 Devor inputs OVAL DATA VALID REM REMOTE D O DATA 7 Outputs DEVICE CLEAR ACTIVE AFTER EOC UNTH TE IN REMOTE ONLY ACTIVE F SPM PRIOR TO AND SRO TO GATE SERIAL POLL RESPONSE TO THE BUS FROM TALK DELAY GENERATOR FROM SOURCE HANDSHAKE TIMING FROM SERVICE REQUEST LOGIC FROM SERIAL POLL MODE LATCH FROM SOURCE HANDSHAKE TIMING FROM SOURCE HANDSHAKE TIMING RECYCLE MODE SELECTED 520 7 SELECTS EITHER CARRIAGE RETURN OR FORM FEED AS A MESSAGE UNIT DELMITER S204 DURING AN LSB FROM THE COUNTER BOARD ACTIVE HIGH WHEN THE FIRST COUNTER tS BEING SENT LOW FOR OTHER COUNTERS CHANGES ON THE FALLING EDGE OF 158 FROM THE COUNTER BOARD OURING DATA OUTPUT CONTAIN THE COUNT DATA SYNCHRONUED TO BYC SENT MOST SIGNIFICANT DIGIT FIRST ACTIVE FOR ALL STATES EXCEPT SPM 54 OR SS GATES BCO DATA wiTH HEADER 13 HEX ROY ANO TE TO THE BUS ACTIVE AFTER LSB TO GATE MESSAGE UNIT DELIMITER TO THE BUS SEPARATES COUNTER OUTPUTS ACTIVE AFTER S4 OF LAST COUNTER OUTPUT GATES ASCII LINE FEED EO TO THE BUS END MESSAGE ACTIVE AT THE END OF OUTPUT TO TERMINATE TALK MOOE DRIVES BUS COMMAND L INE O ENO
112. Such a supply is very compact it is difficult to reach all its components for servicing As an example a NIM crate power supply Canberra Model 7021 is described below see Figs 5 1 and 5 2 5 3 1 General Circuit Description The voltages of the secondary winding of a power transformer are rectified by a bridge where the center tap technique is used Therefore rectifier bridge can generate a positive a negative voltage After rectification there is the classical capacitor filter In addition to six regulated voltages two unregulated voltages are generated by the voltage doubler technique D203 C207 D205 C209 for a positive voltage D204 C208 D206 C210 for a negative voltage to supply the monolithic voltage regulator IC for the 24V line or to bias the driver transistor of the 24V line In order not to exceed the maximum ratings of the 24V regulator the positive voltage is limited by a zener diode An additional 5V voltage is generated by IC 201 All supplies use the common regulator 723 with built in voltage reference source and the possibility of current limitation Dede Ls 1 Positive output voltages The unregulated DC voltage passes through a current sensing resistor to the collector of npn power transistor This transistor is driven by an emitter follower transistor its base is controlled by the voltage regulator The DC output voltage is compared with the internal temperature compensated reference vo
113. TPI 12 24 TP4 12 2 24 5 Fig 9 3 Board locations In the case of failure follow the instructions given in Chapter 6 Section 6 14 Additional useful reading about this type of the power supply is given in the previously mentioned IAEA TECDOC 363 Page 199 If the screen is dark while voltages are adequate the reason might be a bad monitor Continue troubleshooting at MONITOR 174 295 Chapter 9 9 2 2 Central Processor Board If a picture appears on the screen we can check the CPU Central Processor Unit board The analyzer has three built in self testing functions 1 ROM test 2 RAM test 3 Alphanumeric generation test To run a test you have to press YES to prepare the multichannel analyzer to accept your next command Press the hidden key situated as shown in Fig 9 4 You will hear a click and the display shows DIAGNOSTICS CHECKSUM RAM CHAR The CHECKSUM test can be run by pressing YES After 12 seconds the first result will appear on the screen as A28 55E3 or similar The full test takes about one minute The question marks following the chip label are displayed if either the corresponding Ic is bad or not inserted A30 The results of the test can be compared with the expected values given in Tables 9 1 and 9 2 KEY Fig 9 4 The hidden key posit on Selecting the RAM test programme causes the CPU to clear RAM and write known data into it then the content o
114. V 5000V 1 5 10k 500M 10uA 1 10 1 5 10k 0 24 Vac 10 1000V 2 5 200k 20M R 1 5M 1 5 with internal 1 5V battery These kind of instruments have been used for many years and might seem old fashioned nowadays but nevertheless they are often needed where trends are to be analyzed or measurements under floating conditions are to be taken ABC F 45 Chapter 3 26 3 3 2a Digital Multimeter 4 1 2 digit handheld battery powered This type is general purpose useful for bench or field service specifications to 1000V gt 10 lt 0 05 to 750V ac 10M 100 0 2 3 to 200k 0 07 to 300k auto lt 2 to 2A dc lt 0 3 to 2A ac 1 2 Some useful additional features of a digital multimeter Diode test the voltage drop across on a diode can be measured up to 2V with a lmA dc test current Frequency measurement from 12Hz to 200kHz Suitable also for RMS dB relative to a selected voltage conductance relative values offset etc Big display self test different additional display indicators Extensions are available H V probes 5kV 40 current probes HF probes current shunt etc ABC F 46 27 Chapter 3 3 3 2b Digital Multimeter 4 1 2 digit for laboratory and advanced field service battery operated Suitable for long time measurements REL 40000 175 AUTORANGING MULTIMETER BTO ELA ACL Eds 3
115. When counting is finished the resulting number is transferred into shift registers 85 86 87 and 88 Finally the data are modified in four 4 bit adders A63 A64 A65 and A66 The binary number which was loaded into shift registers 85 86 A87 and A88 from the sliding scale counter is now subtracted 2 There is no signal at TP5 STRET OFF might be high In this case the unidirectional amplifier charging Cll is disabled To verify this possibility join pin 9 A86 for a moment to the ground If an adequate signal at TP5 appears the fault is within the ADC board control logic part If the grounding does not restore normal operation the unidirectional amplifier is bad Check all transistors The next possibility is the voltage following the ascent side of the pulse but not dropping back to zero In this case the discharging constant current source 15 not switched on or the source is bad RAMP ON signal A29 pin 6 should be high during the discharge If high state is revealed then the current source is bad Concentrate your observations on transistors Q20 Q21 022 023 026 027 028 and comparator A77 LF411 If RAMP ON is low and discharging doesn t take place the fault is probably in the control logic as before A good test to check a part of the discharging system is to use the fast discharger by injecting a bigger current through transistor Q29 controlled by transistor Q24 the DUMP signal which is normally l
116. a finite resistance across its terminals in which case it is difficult to distinguish whether the wrong value of depends on or on the open BC junction of T2 In such a case first disconnect C on one side and check VB again If VB remains at the wrong value then turn off power and check the resistor values NOTE Some defective resistors exhibit the correct value when measured with the ohmmeter but then present a different value under applied voltage In a difficult case you can consider to replace them even if the resistance measurement gives the correct resistor values The fault symptoms are described in Table 6 4 110 7 Chapter 6 TABLE 6 4 Diagnostics of the fault symptoms of the circuit in Fig 6 3 l C behaving as a short circuit E3 at ground potential VB VBE in the normal range 2 C behaving as a short circuit E3 E2 VB E2 VE E2 3 T2 with open circuited BC junction VB lower than the nominal value by RIR2 IE Rl R2 4 R2 short circuited E2 E2 indistinguishable from 2 and 5 5 Rl open circuited VB E2 VE E2 indistinguishable from 2 and 4 6 Rl short circuited VB El VB in normal range 7 R2 open circuited VB much closer to El than predictable according to nominal values of the components VBE in the normal range 111 Chapter 6 SR Consider now the common emitter transistor connection of Fig 6 4 Besides the faults depending
117. a limit is purely empirical but it helps you to guess whether an oscillation has to be attributed to a component or to the feedback loop The transistor 2 appears to be unneutralized Most likely the oscillation is due to T2 To damp it add a 100 ohm transistor in series with the collector lead at 2 and as close as possible to its can Fig 6 15 Two transistor operational amplifier with signal oscillator If the output signal looks like that of case b with the frequency of the damped oscillation of 50 MHz or less most likely 125 Chapter 6 22 the oscillation is determined by the feedback loop Add then a small compensating capacitor 5pF to 50pF between the collector of Tl and ground The damped oscillation will disappear Look now at the amplifier circuit of Fig 6 16 Suppose you find that its signal gain differs considerably from the nominal value of 10 Such a defect may depend on a change that occurred in one or both resistors because of some kind of accident or on the fact that for some reason the operational amplifier is completely out of specifications as far as its signal gain is concerned In this case the resistors do not draw current in the standing state Turn off power disconnect them from the circuit and measure their values with an ohmmeter If the measured values are close to the nominal ones proceed to replace the operational amplifier The described fault obviously escaped dc analysis NOMINAL V
118. aboratory According to the volume and complexity of the instrumentation the required skills should be determined and on this basis the persons with suitable professional profiles recruited It is highly advisable to recruit for the laboratory such staff members who can cover a wide spectrum of instruments Nevertheless it will be necessary with the increasing demands placed on the work of the laboratory to specialize some of the staff members in particular aspects of nuclear instrumentation Some of the topics of such expertise are radiation detectors analog electronics digital electronics interfacing computers and electromechanical apparatus Note the recent trends in electronics tend to over emphasize digital electronics and computer software development Particularly in the nuclear field there is a critical need for persons with knowledge and experience in high quality analog electronics and this should not be neglected Furthermore it should be kept in mind that many instruments in the nuclear laboratories are not strictly nuclear Electronic balances sample changers optical spectrometers diffractometers and ph meters are research tools that also need maintenance and service and the electronics laboratory should be in a position to offer it The management of the laboratory should design a suitable scheme to evaluate and promote the activities of the staff Special attention should be given to the fact that continuous tra
119. age 25 W Multitip 230 25 Wait Heating up time ca 60s Bit temperature 450 Is Weight without lead 34 g with rubber rest 225 eee Voltages 6V 12 V 24 V 42 V 48 V 110 V 130 V 220 V 240 V Order nos 230 LN 25 WIron with nickel plated copper bit ABC F 230 LD 25 Wiron with ERSADUR long life bit Bits surface like Ersadur type is recommended for all BC F Multitip 230 8 W Multitip 230 15 W Multtitip 230 25 W vernickelt vernickelt vernickelt nickel plated ERSADUR nickel plated ERSADUR nickel plated nickel e nickelee nickelee 132 LN 132 LD 162 LN 162 LD 172 LN bits pannes ERSADUR 172LD 172 SD Cordless industrial soldering iron The cordless industrial soldering iron is powered by long life nickel cadmium batteries which are easily replaceable giving tip performance equivalent to up to 50 watts with over 370 C 700 F tip temperature C F Soldering irons with buthan gas firing with heat regulation and different tips are suitable especially for higher heat transfer grounding in the field service F 34 15 3 1 18 Soldering iron cont d ae plos ix eer 030 KK 30W Iron with copper bit 030 KK 40 W 030 KD 30 W Iron with ERSADUR long life bit 030 KD 40W Lotspitzen bits pannes Kupfer copper cuivre ERSADUR 94 ERSA BO i es 305 er Chapter 3 Wattage 30 W or 40 W Heating up time a
120. all other radioactive test Sources should be removed from the standard geometry area to secure a normal radiation background level It is a good practice to do such measurements a minimum of 1 5 meters above the floor preferably on a plywood platform hanging from the ceiling in a dedicated area of the workshop 11 1 6 2 Dose rate calibration The dose rate calibration of the survey meters could be checked if the activity of the test source is known using the following relationship dose rate hour R h K A Curie R2 m where K the dose rate constant of the used test source A the activity of the test source in Curies R the source detector distance Such check up tests could not substitute the periodical calibration of the survey meter by the National Metrological Institute The expected accuracy of such check ups is better than 20 11 1 6 3 Marginal testing It is important to know whether the battery test green and red areas are valid or not Sometimes the series resistor of the 263 Chapter 11 24 moving coil meter changes its value and batteries might be thought to be good even when they are already bad To test the validity of the indication the survey meter should be connected to a variable power supply and the voltage should be reduced until the measured intensity drops by 10 Then the supply voltage should be increased with one volt and the series resistor of the moving coil meter should be adjusted t
121. als for counting in a proper way In particular this involves checking for triggering at the appropriate levels and for multiple triggering due to cable reflections or other causes NIM positive signals are frequently received at a lk Ohm impedance significant reflections are absent provided the cables are not too long and the signal is not too fast NIM negative signals must be received 155 Chapter 8 22z in an impedance that closely matches the cable Frequently this impedance is made up of a resistor in series with the input impedance of a common base transistor significant impedance mismatch may indicate a defective transistor Discriminator type input circuits most frequently use the 710 or other fast discriminator Good power supply decoupling near the discriminator and a not too small hysteresis are needed to avoid multiple triggering 8 1 3 Output Circuits Output circuits are prone to be damaged improper connections Most frequently however they are just unable to cope with the demands put on them For example a TTL gate or a CMOS driver have a driving capability that can easily be exceeded To drive a terminated 50 Ohm cable one needs a transistorized output stage or a special integrated circuit A check should be made to verify whether legal logic levels are being delivered Output connection to printers or equipment buses 1 addressed elsewhere 8 1 4 Counting Gates Counting gates are open cl
122. aqa x40 070043 440 79 C 4 4 4 4v Ae33 CAPS alr To PEE qus PATA b 9 c 3 43 Coi 10 V INGICATES SHIELD GAB Ta 4 79 4 Cx t lt wel ree lt Janey caran AE lt ares Ct lt jum os 5 i As az sosog lad goog C xi ya faz mors J lu s rx e sooo 7 ph er rj soca Ctl 4 core xi sc lel m 71 Z lect Ci v3 lest gon z ae apos a Co m fal gor E D al et Cis e ar gees BT ses vox pel sese bu esc g 691 712 74 717841 1 74 34195 34 504 74 5140 1 3oo Mute ol c Sea 34811 74 9909 q bra Tal UO 4 ra TED Ou Td SOS nc 1 oA lt MES and Qaa as 13 Say 5 SD lt aM w 4 46 CATED Ae ae 9o TER w moi cC CAP 10 lt Commins AOCAKT ke Fem mont 9C NOUNS FRONT mt LOCAT Q 7 p CASES ADL Cosa test LDC ACA NOLA COLT Oi G r s CagetesATER OER BIA wo AT gt 43 ocak lt Toe ma CA BERAC MES
123. ar ones and not exactly identical a quality control check after repair has to be performed and recorded in a log book This is very important for further troubleshooting Different power supplies are being used in nuclear instruments and in auxiliary equipment that is being applied in nuclear laboratories Typical types of power supplies are i NIM power supply usually about 400W with the following voltages 12 24 12 24 6 6 ATTENTION Some of the NIM power supplies do not have 6V There are NIM modules that require these voltages Some NIM power supplies are delivered in the form of a plug in module these usually have current specifications much less than a normal behind the crate supply Furthermore some of the module connectors in the crate are not supplied with the mains power so a plug in module in such a case would not work ATTENTION The plug in NIM power supplies with their limited power capacity are easily overloaded With three modules inserted into the crate the supply might collapse DO NOT plug such a module into a NIM crate that has a power supply in the back 80 Sq Chapter 5 ii Special supplies for individual instruments such as MCA pulser iii Switched mode power supplies used mainly in computers they are rather noisy and usually not suitable for powering analog circuits iv High voltage power supplies there are sev
124. are taken from medical applications The reader should be able to find equivalent ones in his own field of application RECORDER PRINTEA Low VOLTAGE SUPPLY VOLTAGE SUPPLY Fig 4 1 A typical NaI system Most of the instrument users applying nuclear techniques work in fixed geometry and with fixed HV amplifier and single channel analyzer settings Most of their measurements are relative measurements a comparison is made with radioactive standards Thus when the user or operator says My instrument does not behave as it should one expects that they have not changed their instrumental settings However checking those settings is the first part of troubleshooting since clear distinction must be made between user operator errors and instrument failure Many of the questions which must be asked during troubleshooting can only be answered correctly when instrument settings and previous test results are available in a logbook 69 Chapter 2 4 2 INSTRUMENTS AND SKILLS The following instruments and tools are required for a system check for detailed information see Chapter 3 a multimeter MM an oscilloscope 0 0 15 20 MHz with dual beam dual trace sensitive trigger properties it must be possible to trigger both channels at the same time or alternatively with the signal on one channel and with signal delay lines to enable visualization of the front edge of pulses
125. ave rt DCHAL TP26 DMA REQEN TP27 Data valid Qn DMA DATA V1 TP2o 1 finished RST 7 5 amp TP10 PRS TP28 reset when power on gt VID sending data OUT TP23 TP LSYNS ADC dead time data LT A27 pin 11 TPL FSYNS Fig 9 7 Display board connections 9 2 5 Principles of the ADC Operation ADC tells the height of the input pulse in a binary way A simple example of the operation of two and four channel converter is given in Fig 9 8 0 1 00 01 10 11 Fig 9 8 Two and four channel pulse determination In the first case the height of the input pulse U was grouped into channel O while in the second case the voltage was found in channel 10 10 3 expressed decimally However to determine the pulse height more precisely more channels are required Contemporary multichannel analyzers have up to 16384 channels To express this number in a binary way 15 binary digits are required Conversion from the analog to the digital form takes some tens of microseconds The conversion time of course depends on the conversion method The widely adopted converters in nuclear instrumentation for which the operating principles will be briefly described are of the Wilkinson type 180 9 Chapter 9 QUTPUT uu c IS DVER INPUT Fig 9 9 What STRETCHER does Fig 9 10 Simple STRETCHER followed by 90 discr Gaussian pulses Fig 9 9 from amplifiers keep their maximum value only for a short momen
126. ays may easily give trouble Frequently this is due to short circuits or misconnections in LED displays and to improper contact in the conducting path usually at the rubber glass junction of LCD displays These are also prone to malfunction if excess humidity provides leaky paths for the segment voltages Faulty capacitors may be responsible for a total failure if they are short circuited or just to degrade performance of the instrument if they do not adequately by pass spikes or glitches to ground a much more difficult situation to troubleshoot 8 2 2 Checks at the Block Level The input block must be seen to give a single pulse for each pulse received even if the pulse has a reasonable amount of noise a pulse generator will help to determine the triggering threshold If the input is supposed to work on analog signals multiple triggering is more likely to occur with slower signals a sine wave with the negative half wave clipped to ground by a diode is a suitable test signal If multiple triggering occurs with the threshold well above noise level the hysteresis circuit of the comparator must be checked Pulse pair resolution is determined either by the input block by the first counting circuit If otherwise unavailable a simple test instrument can be built around two 74LS221 integrated monostables and an OR gate as shown in Fig 8 2 cc Lo LJL Fig 8 2 Double pulse generator with adjustable separation between pulses
127. bad rectifier bad short circuit oscillator bad regulator bad Q105 short C115 bad transformer bad rectifier bad R131 broken CR103 broken Q103 short R131 misadjusted short circuit broken cable bad connector short circu t blocking osc bad short CR105 broken C103 CR106 R11i short n transformer broken coil bad regulator broken R110 R104 misadjusted bad M301 tube bad Z201 determine why replace replace replace determine location repair replace bad component replace bad component replace bad component repair replace replace replace replace readjust determine location repair repair replace repair replace locate repair locate and replace replace component replace component repair replace repair replace locate replace replace readjust test replace test replace Signal too short Pulse rate higher than reference value with stan dard source and geometry Pulse rate lower than reference with standard source and geometry Scintillation sonde no low voltage No detector voltage Detector voltage high Detector voltage low sad bad C201 C202 R205 bad cable connector radiological conta mination too high detector voltage faulty tube fault in main unit too low detector voltage increased dead time Fault in main unit broken cable bad connector contact oscillator bad Tl bad Q101 or Q102 bad 2201 bad R401 or CR201 bad
128. be signals from A8 a counter that moves with the same clock A32 that actuates the scanning circuits included in the LSI counter A54 The scan reset input of the LSI pin 1 is used to assure the synchronism necessary for each digit to display the corresponding decade The scan reset input signal can be made synchronous with the signal strobe 1 in which case the display 161 Chapter 8 8 shows decades D5 to DO or with a signal that appears two scanning clock pulses before strobe 1 in which case the display shows decades D7 to D2 This scale selection is made through multiplexer A38 the address inputs of which are driven by the appropriate signal from the LSI scalers of channels A and B through flip flop and a gate as shown in the block diagram Fig 8 4 Block diagram of the display section of dual counter Canberra Model 2071 A short guide to troubleshooting the main points of the display section of the instrument is given below 8 4 1 Scanning Oscillator and Counter Scaling Circuit Check for the oscillator signal at the clock input of counter A8 pin 14 if it is not there check at the output of A32 pin 3 where a rectangular wave with the high state twice the width of the low state should be seen If the oscillator is working and signal is present at the clock input of A8 go back to the oscillator through gates Al5a and Al2 disconnect the daisy chain option if necessary With the clock signal on obser
129. ced raster Scan format The major difference is that the CRT yoke is turned 90 degrees causing the vertical field to force the beam to run fast from the bottom to the top of the screen and slowly advancing from left to right making the first 256 runs before it returns to the left where it starts to make the second set of runs between the lines written during the first set see Fig 9 6 age 502 s 510 8 10 EVEN FIELD 496 500 504 508 d INTERLACING RASTER TYPE DISPLAYS LINE BEAM L TRAVEL LFIELD 57911 FIELD 497 eo 505 499 503 507 511 Fig 9 6 Resultant interlaced frame obtained from odd and even field scan During scanning the electron beam striking the CRT screen should be properly intensified to draw the wanted pattern This is done by applying the modulated VID signal to the CRT control electrode The modulation information is gathered from different sources Text is provided from ROM Spectra representing points are contained in the RAM Both information sources are on the CPU board Fast operation is obtained through direct memory access DMA while the 8085 processor is in the HOLD state See Fig 9 7 for the connections between the DISPLAY UNIT and the remaining system The dead time counter signal is produced on the DISPLAY board using the LT line from the ADC board 179 Chapter 9 8 BADO BAD7 AIS Lll pM ADDRESSES I want DMA DCARI TP15 You h
130. cleared A pulse of gt 50 is required 32 ERROR Out This output goes LOW when the printer is in PAPER END state OFF LINE state or ERROR state 33 GND In Same as pin 19 to 30 34 NC Not used 35 ON Out Pulled up to 5V through 3k to indicate the 45V supply 36 SLCT In Data entry to printer is only possible when this signal is LOW If you are going to make your own cable to connect a printer to an IBM compatible PC be careful You will find instead of a 36 pin connector a 25 pin one similar to the one used for RS 232 The circuit diagram Fig 10 5 will help you to find the right signals on the PC board At the same time it will show you how a parallel interface is built up The 8 bit databus is connected over tri state driver circuits direct to the connector To transmit data 018 U4 Ull and U16 are used To receive data U9 Ul16 U8 and Ul are used The following timing diagram Fig 10 5 shows you the relation between STROBE DATA ACKNLG and BUSY SIGNAL You can check it with normal dual beam oscilloscope As mentioned before it is very important that rise and fall times of each signal must be less than 0 2 us BUSY ACKNLG DATA STROBE Approx 5 us 95 ns Min 05 ps Min Fig 10 5 Parallel interface timing 223 bcc Bert 1 SH A IST ty 49597 1 mera seat 1 mnt v ISl n ibat 1 f 51 1 sary SAT n Set i
131. configurations location of the power inputs and signal lines It is not important to memorize these pins however In two minutes time one should be able to list the expected voltage levels and signals on a 14 pin IC after looking on its diagram and the specifications in the catalogue A nuclear electronics service man should be able to discriminate between filtering circuits around the power lines and frequency characteristics determining components round amplifiers They should be able to correctly group such components at a rate of four items per minute In some circuits the feedback loops are rather elaborated However they should be correctly identified as the time limit is one hour The real test of understanding a circuit is if the electronician can prepare correct functional diagram of the circuit The general rules for producing functional diagrams are the main signal flow must be from left to right the signal flow must be emphasized this can be done by showing flow paths in a straight line avoiding crossover of flow paths arrows may be used to indicate direction of flow only to avoid ambiguity main inputs must be on the left and outputs on the right the source of all inputs and the destination of all outputs must be shown all plugs sockets controls test points and terminals useful in troubleshooting must be shown and referenced normal state measurements for all test points must be available
132. d By regular bi monthly battery compartment check ups such failures could be eliminated In case of the Ni Cd battery option one might expect to find an indication on the display if the batteries are already charged After a long unused period they might be discharged If the DSI LED lights up after the mains is connected it proves that the cord connector fuse and the transformer are functioning 251 cec Fig 11 9 Wiring diagram of a survey meter OPTION ACCUMULATEURS 3 at CHARGEUR 21 34 13 Chapter 11 If the fuse is blown out one should suspect first the Ni Cd batteries for short circuit and the CR201 rectifier The test should be repeated with the 14 pin socket detached if they prove to be good because then the short circuit is further away from the battery It is good to know that the Ni Cd accumulators have a limited life which might be reduced by neglecting the periodical chargings A Ni Cd cell still working after four years is of an exceptional non standard quality Civ The first DC DC converter The voltage from the batteries or from the accumulator changes during use To overcome this a regulated power supply feeds the circuits with 12 volts A self starting power oscillator 9101 0102 drives the T101 transformer If the emitter current of these transistors exceeds a certain limit the Q105 transistor pulls to ground the base of the series control power transistor
133. d LMP 179 B 62S L SnPbAG1 8 solder of galv silver SN63 183 A SN63 L Sn63PbB103 printed boards 60 40 188 B DP G L Sn60Pb electronic SAVBIT 6 190 G L Sn60PbCu2 stops disintegra tion of cu 50 50 212 B F G L Sn50Pb electronic SAVBIT 1 215 G L Sn50PbCu stops disintegra tion of Cu 965 221 A Sn96 B 96S G L SnAg5 without lead 40 60 234 B G G L PbSn40 common electric 95 243 95 L SnSb5 without lead 30 70 255 B J G L Pb70Sn E Motors 20 80 275 B V G L Pb80Sn lamps HMP 301 B 5S high temp solder Chapter 3 2123 Ditferent amount of these elements result in alloys with different characteristics like melting point conductivity agressivity to other materials copper mechanical strength etc 370 315 This diagram shows a 260 solder wire composi lt tion of tin lead 2 20 2 There is a paste 5 19 region above and g below the 63 tin a 93 concentration 38 Tinn Sn 95 53 Eutectic point Di Zir Flux is necessary to allow soldering or to make it easier Normally the flux ought to be inagressive especially against copper During the soldering procedure some important considerations must be followed After switch on of mains the soldering iron should heat up fast and should remain at a constant temperature During the soldering period it should warm up fast the material of the soldering point to a temperature close to the liquid region of the solder Adequate solder ha
134. d 3 are similar in their configuration and must be made out of discrete components due to noise rise time and overload recovery requirements In the integrators monolithic operational amplifier circuits can be used because the pulses are already slowed down In the baseline restorer comparators are used The pile up rejector receives a signal from the third amplifying stage and provides a TTL compatible signal For croubleshooting it is necessary to follow the rules listed below 1 Switch off baseline restorer 2 Switch off pile up rejector 137 Chapter 6 Spectroscopy amplifier circuit diagram 6 23a F g 138 Chapter 6 35 e 001059 e E F vat LST nc tes gt per mm SeT f SQevod 2 A328 ow Aen ry PRIS pur ear Spy wh w s Biv ND Cure s c POOP t gt 4 2 491720497 et we 100 py 438 Jeg W 31 w Psa O9 S owned noes Ly Ooy Faw t yYy ppJsv groe sueter JIN Efi JRE ENS 4 w sie w ONOG MOD SPINS YD C9 WOM gm 1 Se 72 FINITE F310 gt M or yt Mat Mews o wor IIAN ERLI ei COuSm GPOYPNS 230 i0 Wwe Og ss Seow Meo uses Darum SIINNE gt ONPE dem wasn W
135. d successfully then we can assume that the CPU board is working properly 9 2 3 Monitor The MONITOR is a self contained assembly which includes the CRT and the necessary electronics to present a TV raster display It should be considered as a replaceable component and is not intended to be repaired in the field It accepts three signals video VID line synchronization LSYNC and field synchronization FSYNC Signals can be observed Fig 9 5 at the 10 pin connector as follows PIN 1 GND PIN 6 LSYNC PIN 7 15 V PIN 8 VIDEO PIN 9 FSYNC PIN 10 VRTN Video ground PIN 10 is the lower one Even Field LSYNC eS e J pi cp FSYNC Field Sync Horizontal fr St 538145 Fiel Odd Field EY 269 5 LSYNC Line Sync cr ala z j j _ FSYNC Field Sync 1p Fig 9 5 Synchronizing signals 178 ul Chapter 9 In the absence of any of these signals the MONITOR screen will be black Troubleshooting should be concentrated on the display board It is useful to know that the MCA is able to show the display field on the MONITOR with the LOW VOLTAGE POWER SUPPLY and DISPLAY BOARDs inserted even if all the other boards removed 9 2 4 Display Board On the DISPLAY BOARD three signals for the MONITOR control are produced LSYNC FSYNC and VID as already mentioned The first two signals are used to control the MONITOR picture Analogous to a TV monitor a MCA display is an interla
136. dAL HO IOO HLIM GWGH NOILOW SSIM SNI T NSAING SNILNOdd S HOLOSLILS3G Main mechanical elements of a medical scanner 11 13 Fig 267 Chapter 11 28 11 2 3 Controls Turning On and Quick Checks The nuclear channels are controlled by the ISOTOPE SELECTOR see Fig 11 14 this switch or push button adjusts the energy and window settings optimal for the isotope used If they are not periodically checked for accuracy poor pictures might result In most systems MANUAL ENERGY and WINDOW controls are also available If the manual and the preset adjustments give different results it s time for readjustment and calibration ISOTOPE SELECTOR 5 4194 IFT PRESET COUNTS SEC MODE SELECTOR MANUAL COUNTING RATE METER RANGE SELECTOR Fig 11 14 Nuclear channel controls The counting rate meter range adjustment is conventional If a radioactive source is introduced into the field of view of the detector and the corresponding preset or manual energy and window selection was done the display meter should indicate changing values as the source is moved under the detector An example of the front panel of a scanner control is shown in Fig 11 15 BLUE YELLOW VIOLET COUNTS cm SPEED m min INFORMATION DENSITY COLOR DISPLAY CELTI o STEP SIZE OFF MANUAL SCANNING POSITIONING COLOR ADJUSTMENT MAINS Fig 1
137. dback resistor the current to voltage conversion rate changes as well the smaller the resistor value the smaller will be the voltage output of the amplifier for the same current Sometimes the output of the amplifier drives the 243 Chapter 11 4 moving coil meter directly in some other designs an additional bridge circuit serves the same purpose Linear and logarithmic scale versions are available to display the dose rate The ZERO SETTING control potentiometer acts on the non inverting input of the differential amplifier In some designs a low pass filter smooths the movement of the moving coil meter and other circuits protect it from overloading RESISTOR IONIZATION CHAMBER z ERO SETTING DETECTOR LOW VOLTAGE BATTERY BIAS SUPPLY SUPPLY Fig 11 4 Diagram of a survey meter with ionization chamber 11 1 3 2 Survey meter with Geiger Mueller tube Fig 11 5 A DC DC converter supplies the Geiger Mueller tube with its operating voltage On the load resistor of the tube voltage pulses are developed for each ionizing interaction if the appropriate dead time has elapsed since the previous detection The pulses need to be standardized in amplitude and length and monostable circuits are used for this purpose In some designs the pulse length determining components R or C are modified on different dose rate ranges so the signals after integration can directly drive the moving coil met
138. diagram of the instrument is shown in Fig 7 1 OUTPUT DRIVERS 07 011 Fig 7 1 Block diagram of timing SCA The baseline and channel discriminators compare the input analog signal amplitude to the preset voltage levels V E and AE The output of the discriminators is combined the block labeled SCA logic to produce an output if the SCA conditions are satisfied that is if the baseline discriminator is triggered and the channel discriminator is not triggered The output signal is delivered to the output drivers at an instant determined by the timing discriminator A more detailed analysis of the various circuit blocks follows together with troubleshooting guides 7 2 1 Level Setting Circuitry The comparison level for the baseline discriminator is set by the circuitry around A9 which is wired in a voltage follower 145 Chapter 7 2 configuration From Fig 7 2 you can see then that the input voltage to A9 pin 3 comes from the NIM 24V supply if this voltage changes for example due to load changes in the NIM crate see Chapter 5 Power Supplies the output of A9 is bound to change To check whether the circu t is working Properly verify if the output voltage pin 6 is equal to the input voltage pin 3 at the extreme positions of the RV8 helipot range the trim potentiometer RV5 should be adjusted so that at the lowest voltage in the range the output voltage equals the voltage at pin 3 at the up
139. e and of emitter follower Q4 which is the output stage Transistors Q5 and Q6 are current sources respectively absorbing the collector current of Q3 and forcing the current into the emitter of 04 The pole zero adjustment network consists of potentiometer RV2 of resistors R8 R18 R27 and of capacitor C6 Transistors 07 08 09 010 and 011 constitute a discrete component operational amplifier whose gain can be fixed to l or to 5 with the jumper connected respectively between A and C or A and B 6 2 1 2 DC analysis to the charge sens tive loop Take out the sliding lid connect the preamplifier box to earth and switch power ON 129 OED 002 814 02 9 E QE I ROR r DE COTTON gt 9 191deuj5 VHH398NVO JO 12 s NOTES THERE ARE NO 4 WKY TES ON T SCHEMATIC 2 UNLESS NOTEO ALL RESISTORS ARE kw 51 2e X WwOCATES QuGOC RESISTOR IT 24v 4 INDICATES MPO CAPACITOR 5 NOACATES POUYCAG amp amp CAPACITOR NOICATES AMP SOCKET 2 9 x paces CAMEO SOCKET Q4 TH QU CONTAINED IN Al AGA ev m i v a Fo PA SEE DWG A 11290 COENITE SEE icn 31650082 4 ey Kiz aenn N Jz 73347 ER X CA cun J zr zn r Joco Co Ri gc heel 24y E TS rates horn 5 INTEGRATED Citxurr RES STO Rz CAPACI TOS TRANSISTOR Ql
140. e 5 DATA y evr por C amp 148 it aim 1a paa 21220 CARLA PC Amur Coot fue av any ROM Gant v meu vio Xx PA TO von 4 OET rm A ng v wean oto 2 Len ror or tsr Pomir mur 99 r ard ane a Mar 14 6 nr 24 4 Co amad E Como 1432 A3 128 v 2 426 a e 2 wt mast Low brew Fou Stat trr Count pare Gart Fig 9 28 Data point video Selection is done by multiplexer A68 A69 which is controlled by another multiplexer A67 Multiplexer A67 allows the selection of linear or logarithmic display and the selection of the vertical scale The conversion to logarithmic format is performed in ROM 71 and the result is stored in latch A72 drawn in sheet 3 top Simultaneously the counting of DTCK clock signal TP6 in 8 bits line resolution counter A49 A50 starts The line resolution counter is periodically cleared by TP16 During counting the electron beam in the CRT climbs up along the line At the moment when the content of the LINE RESOLUTION COUNTER is equal to the channel content number stored in 72 the 8 bit binary 198 27 Chapter 9 comparator A53 A54 delivers the pulse at the output A B A54 pin 6 This pulse is used to intensify the electron beam at the prope
141. e JFET it is definitely damaged and has to be replaced If however current flows in the JFET and this current is not smaller than 5mA it is worth going to a dynamic transconductance test according to the circuit of Fig 6 216 For detailed information about FET tests read IAEA TECDOC 309 pages 78 through 81 b The FET exhibits an open channel with the test of Fig 6 2la value of gm which is typically below 10 mA V proceed to its replacement Actual FET replacement is not a simple operation because most commercial charge sensitive preamplifiers employ SELECTED FETs If the type of FET is specified you can try to purchase some of them and then make a selection choosing according to the procedure outlined in IAEA TECDOC 309 the specimen which has the largest gm Pay attention however to the following point If you do not want to change other components in the circuit the new specimen should also be not too different in IDSS from the previous one The current actually flowing in the FET is given by Vl VA R1 For instance with the components of Fig 6 20 VA 4V the current in the FET is approximately 28mA Therefore your new FET should not have an IDSS below 30 mA but should also not exceed IDSS 40mA Things are more complicated when the FET type is not specified or if specified is not available The replacement then will rarely be completely satisfactory and the original noise performances will mot be
142. e Regele nhe t electron control unit Digitalanzeige No TCS 800 electronic control unit j with digital display i No TCS D 800 EE ENES i ei Entlotkolben desoidering iron No 600 600 CO No 600 AE Ablagestander holder Ablagestander holder No 13 ungeregetter Lolkolben im 24 V bis BOW Lotkolben 24 V bis BO W unregulated regulated in the handle 1 24 V up to 80 W 24 V upto 80 W Fu elektr iter bi teas Regeleinheit elektronische Regelemhert witch IOC control unit mt Oignaianzeige FES 820 D No TCS 800 electronic Control unit No with display No TCS D 800 Ablagestander amp holder No 09 37 Chapter 3 18 3 1 19 Tin As shown on page 11 Table 3 1 one should also select for a special purpose the adequate solder In real life however one to three types of tin alloys will be enougn 60 40 with low melting region BC Savbit 6 protects copper F Savbit 1 protects copper higher melting region BC Tin of multi con type with non corrosive flux like rosin should be selected The quantity is normally 100g 250g 500g per unit A handy dimension gives the 250g spool The diameter of the solder wire should be about Imm only for tiny circuit work small spool of about 0 3mm diameter solder wire is recommended to have on stock C F 38 19 Chapter 3 3 1 20 Des
143. e rather dangerous in repair work and it should be avoided by employing personnel without this deficiency It is very important to be able to locate certain components on the circuit board from the circuit diagram and vice versa Skills can be quickly developed by training An acceptable level is demonstrated by being able to correctly locate ten components both ways in ten minutes The capability to locate components running at high voltage is a needed skill in nuclear instrument repairs The repair personnel should be able to correctly mark with red pencil all high voltage lines and components on the diagram within 30 minutes and they should be able to locate the same in the instrument as well In many systems interlocks fuses and thermo switches might inhibit operation due to present or past hazard situations Often 63 Chapter 3 44 they are connected to logic circuits timers etc The technicians should be able to correctly identify such circuits within ten minutes Circuits can be inoperative because of faulty switch functions It is important to be able to identify which circuit points should be connected together to secure operation and which lines should be cut Such decisions should be correctly made within five minutes Signal propagation determination is very important This can be a complicated task The general rule is to find each active components inputs and outputs This requires familiarity with the IC pin
144. e state bidirectional transceiver 7415244 A65 A72 The data from the upper four lines between transceiver and RAM can be stored in latch 7415373 A75 in order to avoid false data registration in some phases of the programme Read or write access to is determined by WT signal pin 27 The same signal is used to control A65 Addressing is achieved through 14 address lines Lines AO to A9 are directly connected to chips They come from latches 8282 sheet 4 Signals PO Pl P2 and P3 indirectly involved in the addressing are generated by the programmable chip A26 sheet 5 It accepts the address lines from A10 to A15 from circuit A47 and provides outputs with respect to the memory organization Three of the generated lines PO P2 and P3 are used as the remaining three address lines Pl line together with the latched 12 and 15 address line is applied to A62 3 to 8 lines decoder Output pins 4 5 6 and 7 of 62 are used to enable RAM chips 191 Chapter 9 20 The battery charger sheet 5 connects the rechargeable NiCd battery to the 5 V source when power is applied If 5 V is present the current to the base of Q4 keeps it conducting The resulting current sinking from the Q5 emitter into the Q4 collector through R61 also makes Q5 conducting 9 9 DIRECT MEMORY ACCESS Direct memory access DMA is used to allow high speed data exchange between RAM and an external device The operation of the system und
145. e sweep of 100ms will show that there is some negative voltage about 12V on the output This you can see if you switch the oscilloscope from DC to GROUND operation Slowly start to increase the voltage say about 100 V per second If you stop for a moment at 300 V you will see on the oscilloscope the picture as shown in Fig 12 2 After a few seconds the sawtooth shape of the signal will become stretched out Fig 12 3 until you see only a straight line Now the voltage can be increased to the prescribed value 283 Chapter 12 2 6 Fig 12 2 Scope shows sawtooth shapes when h gh voltage is applied to an optical feedback preamplifier Fig 12 3 In a short time the shape changes to a low frequency saw It is time to put a radioactive calibration source the detector It is preferable to use a Fe 59 source emitting x rays of 5 9 keV If you do not have a calibration source use an excitation source a suitable holder and place a sample that contains mainly iron in the position of the sample on top of the holder If the counting rate is high the sawtooth will appear again Increase the sweep frequency and the vertical amplification of the oscilloscope and you will observe the steps on the increasing line of the sweep Fig 12 4 284 7 Chapter 12 Fig 12 4 Shape of the preamplifier output with x rays coming into the detector The detector and the preamplifier are working 12 1 4 2 Reso
146. e variac Here you will already have some indication as to where the short circuit might appear i Less than 4 of the ac line voltage indicates a defective line filter network or a faulty transformer ii About 4 of line voltage can indicate a bad transformer or a bad rectifier Separation of transformer and rectifier diodes or bridges has to be made to define the defective part of the supply iii 6 8 of line voltage indicates a short circuit either in the rectifier part or a defective filter capacitor by separation of these two parts of the power supply it is possible to detect the defective component iv 8 105 of the line voltage indicates a short circuit after the pass transistor and the current limitation jis not working properly therefore all output voltages have to be measured to locate the defective component The semiconductors must be checked in the conventional way In measuring base emitter voltage around 0 7V collector emitter voltage must not be less than 0 7V otherwise the transistor would operate in the saturation region and would no longer be l near If these voltages are completely different as previously mentioned remove the transistors and check it again To check the operational amplifier its two input voltages should have the same value If they do not compare them with the output If there is a discrepancy remove this operational amplifier 92 15 Chapter 5 After replacing the defecti
147. ectrum with the 1 3 MeV peak and determining the FWHM from the plot Put all the conditions of the measurement and the results ina log book together with the copy of the certificate 12 1 3 2 Efficiency determination Efficiency is a very important property of a high resolution gamma ray detector The Ge detector efficiency is defined as the net area under the Co 60 peak at the energy of 1 3 MeV compared to the net area under the same peak measured with 3x3 inch Nal detector efficiency is given in 4 Place a Co 60 calibration source at a distance of 25 cm from the surface of the 3x3 inch Nal detector take the spectrum and determine the area under the 1 3 MeV peak Repeat the measurement with the Ge detector under identical geometry The ratio of the intensities gives you the efficiency eff I Ge x 100 I NaI 282 aiu Chapter 12 Some other very important information that tells us about the quality of the detector is the dependence of the efficiency on the energy of the detected gamma rays A number of methods have been designed for accurate measurement of this property and computer programs are available for evaluation of measurements The simplest methods involve the use of a set of calibrated gamma sources For details see A Guide and Instruction for Determining Gamma Ray Emission Rates with Germanium Detector Systems by K Debertin May 1985 12 1 4 Si Li and Planar Ge Detector They are for high res
148. ed by series of decade counters according to the range selected It is the rate of the output signal from this block that s determined by the instrument We just refer to the part of the instrument responsible for this determination for the other one is just another example of a counter The block d agram of this part is shown in Fig 8 5 a short description of its operation follows TIME MARK Fig 8 5 Block diagram of part of digital linear ratemeter Events are counted in the 6 bit counter during the interval between time marks 0 55 or 5s in the lowest rate scale At each time mark the contents of the counter is transferred to either latch A or latch B according to the state of the flip flop after transfer the counter is reset and a new cycle starts The contents of the two latches corresponding to successive time intervals are added and the result is applied to the digital to analog converter The output of the converter is read by a meter either directly or in the lower ranges after averaging 8 5 1 Counter Latches and Adder Start by checking if the event signal is present at pin 5 of 4 bit counter A8 Reset pulses must be seen at 14 of 8 and pins 1 and 13 of 2 bit counter A9 A8 and A9 form a 6 bit counter these reset pulses are separated by 0 55 5s in the 10 counts sec range and care must be taken if they are to be observed in a Scope Observe also the clock inputs of the A6 and A7 latches pin 1
149. ed person who received proper training in servicing of nuclear instruments can easily find a well paid job in private enterprise and would thus be lost for the nuclear laboratories Accordingly it is not easy to create a team and a laboratory for nuclear instrumentation service In an average laboratory the maintenance and servicing abilities are hardly transferred to the junior staff It takes much time to acquire the necessary skills for instrumentation repair and it is difficult to share the experience within a group In many developing countries there is no alternative to the decision to create and support a maintenance and repair service Depending on the size of the country and on the amount of nuclear instrumentation in the country it might be sufficient to establish one central laboratory or it might be necessary to plan for more of them strategically located in different parts of the country This laboratory or laboratories should be suitably staffed and equipped and should maintain a documentation library with data books copies of all manuals catalogues of equipment supplies and a selection of electronics textbooks a stock of components and spare parts if possible a stock of spare instruments maintenance k ts It is obviously not easy to create and staff such a laboratory in a developing country The present publication should provide some help in this difficult task 10 Chapter 2 ORGANIZATI
150. eplaced It might happen that the oscillator will not start because either CR104 or CRIO5 has a short circuit this could be checked by disconnecting them from the circuit Another reason could be a short circuit in the transformer This can be checked for with the previously described blocking oscillator test 253 Chapter 11 14 9103 can be replaced with two transistors in Darlington connection v The Geiger Mueller probe The circuit diagram is illustrated in Fig 11 10 The detector voltage is developed in the DC DC converter on the left A blocking oscillator composed of Q105 and QI106 generates the detector voltage which is doubled with the use of CR105 and CR106 and the capacitor C103 The high voltage is filtered by C104 and C105 A fraction of the high voltage is fed back to the 09101 9102 composed differential amplifier There are two non common circuit elements the CR101 and the CR103 they are current sources composed of two transistors in Darlington connection After 0103 emitter follower output of the long tailed pair is further amplified by Q104 If there is no detector voltage first the blocking oscillator should be tested for operation If the base of 0102 is driven from outside with a variable voltage from a helical potentiometers wiper the operation of the amplifier stages could be easily checked The secondary winding of such transformers is rather vulnerable if it is exposed to humid climate
151. er 27 28 1 50 77 80 64 All A80 64 77 80 64 63 A30 A63 A53 A53 A53 A64 A67 74 67 67 A74 A67 A74 A67 Series 354 checksums for V 1 00 Option Number BASIC BASIC BASIC BASIC 354 3541 3541 3541N 3541N 3541N 3541C 3541C 3541C 3543 3543 3544 3544 3551 3552A 3553 3554 3571 3571 3572 3573 3573 35738 35738 3574 10 Number 900069 900069 900070 900070 900071 900071 900071 900072 900072 900072 900073 900073 900073 900074 900074 900075 900075 900076 900077 900078 900079 900080 900080 900081 900082 900082 900083 900083 900084 PROM TYPE 27128 21128 2716 2116 2716 2716 2716 2716 2716 2716 2716 2716 2716 2132 2732 2732 2732 2716 2716 2716 2716 2716 2716 2716 2716 2716 2716 2716 2716 Chapter 9 z The following messages are expected as a result of testing RAM TESTED O K if good or RAM FAILURE N if bad N indicates the failure type and has the following meanings lMemory won t clear 2Memory integral incorrect positive slope 3Memory integral incorrect negative slope 4Flag bit incorrect Selecting the CHAR test programme will cause the display to show two lines of the alphanumeric character across the bottom of the display By pressing the hidden key again the diagnostic is finished If all three tests have been complete
152. er resulting in a linear dose rate scale In some systems after the integrating amplifier a logarithmic amplifier is employed to give a three four decade display span In order to improve the shock resistance of the system in new designs they often use digital counters with timers instead of the moving coil meter INTEGRATOR GM TUBE PULSE NORMALIZATION BATTERY Fig 11 5 Main components of a G M counter LOW VOLTAGE SUPPLY DETECTOR BIAS SUPPLY 244 5 Chapter 11 11 1 3 3 Survey meter with scintillation detectors A DC DC converter supplies the photomultiplier with the necessary voltage The current output of the photomultiplier is a function of the interacting particle energy In very wide energy range the current pulses ar e integrated and converted to voltage signals to drive the moving coil meters Such systems are often combined with logarithmic amplifiers to cover many magnitudes in dose rates In ore prospecting clinical and industrial applications another popular version consists of a complete single channel analyzer with either a counting rate meter or a scaler timer sometimes with a digital ratemeter 11 1 3 4 Survey meter with semiconductor detectors A DC DC converter supplies the detector voltage The signals after linear amplification are passed to various pulse shaping and modifying circuits In most versions multi range counting rate meters develop the dr
153. er the DMA conditions is shown in Fig 9 20 The controller see sheet 5 for schematics provides three operating modes Read Write and Read Modify Write R M W DATAV REQEN WTDTA lt x o Encoder and Buffer Timing Generator DCHR1 RAM Controts Priority DCHR2 Encoder Butter Controls HLO ACK DCHR3 Fig 9 20 DMA realization The controller can accept three direct memory access requests DCHR1 DCHR2 coming either from the Display Board or from Collecting Interface Miscellaneous Boards The third one DCH3 might be used by the boards inserted into the option board slot In combination with the clock signals the DMA request is confirmed through the DCHAl line TP2 and through the DCHA2 line TP3 These signals are sent back to the DMA requesting units Simultaneously the microprocessor address and data lines are tri stated through the hold command HDRII When 8085 acknowledges the HOLD command it generates the HDAI signal This signal starts the operation of the timing generator In the timing generator A34 and A3 followed by some logic A2 A7 A18 different DMA cycles are composed See Fig 9 21 and Fig 9 22 for the generated signals 192 Chapter 9 21 TP3 TES TP14 TP25 Address Latched Here Address Latched Here Le 83 nsec 1 I U 9 21 Fo s3 nsec 3 4 re 5 1 i 1 1
154. eral different types depending on the requirements of voltage current and stability NOTE HV Supplies are designed as DC DC converters and very seldom as switched mode power supplies 5 2 TOOLS INSTRUMENTS COMPONENTS RR Below is a list of the most essential tools instruments and electronic components needed in repair and servicing of power supplies in nuclear instruments TOOLS Pliers cutter tweezers solder iron desoldering tape INSTRUMENTS Voltmeter digital ammeter 5A variac 220V 3A 50Hz Power supplies either a NIM crate with power supply or two DC supplies 0 30V 1 Oscilloscope 30MHz Variable power resistor 100 ohm with up to 3A load capacity such a power resistor can be easily made using a power transistor on a heat sink controlled by a potentiometer at its base COMPONENTS Rectifier diodes 1A 3A Usp 700 1000V Rectifier bridges 5A 25 Usp 200 500V Transistors 2N2219 2N2905 2N3904 2N3906 2N3055 BD651 MJE 371 MJE 321 Thyristor 2N4441 81 Chapter 5 4 set of zener diodes from 5 1V up to 24V Switching diodes Operational amplifier LM356 or LM741 or almost any other internally compensated amplifier Electrolytic capacitors 1000uF 35V 63V 4700uF 35V 10000uF 25V Tantalum foil electrolytic capacitors lOuF 35V 5 3 BEHIND THE CRATE NIM POWER SUPPLY A very common power supply is the one behind the NIM crate
155. eral signals at the test points and compare them with the manual 141 Chapter 6 38 from double pulse Rl Dl generator to amplifier input double pulse generator settings without load var 3 100ps Fig 6 24 Check circuit which enables you to check the pile up rejector 142 Chapter 7 DISCRIMINATORS SINGLE CHANNEL ANALYZERS TIMING CIRCUITS ms Chapter 7 7 DISCRIMINATORS SINGLE CHANNEL ANALYZERS TIMING CIRCUITS a eos a I il Bs E Traiano 7 1 INTRODUCTION The fundamentals of amplitude analysis and time measurement in nuclear electronics have been dealt with in IAEA TECDOC 363 to which the reader is referred Here we limit ourselves to a discussion of commercially available instruments from the viewpoint of maintenance and troubleshooting Apart from a few examples discriminators are available just as part of single channel analyzers The exceptions generally apply to instruments intended to accept pulses coming directly from photomultipliers in fast amplitude and time measurements Although they are not referred to explicitly in what follows the discussion is in broad terms also relevant to them To be useful in different applications the output signal from a single channel analyzer frequently contains both amplitude and timing information Circuits related to each one of these parameters are discussed below 7 2 AN EXAMPLE EDGE CROSSOVER TIMING SCA CANBERRA MODEL 2037A A block
156. ered by capacitors Cl C2 and transformed by Tl This transformer is controlled by power MOS FET Ql which is controlled by IC Ul via transformer T2 Note line separation can be achieved only transformer or opto coupler depending on the power which has to transferred On the secondary side of the transformer the line is rectified by a fast switching diode bridge D2 filtered by inductance Ll and Capacitors C5 C6 The pulse width modulating integrated circuit Ul has besides regulation the capability of current limitation with foldback characteristics The current is sensed by the resistor R5 If overvoltage occurs for any reason a crowbar circuitry is fired IC U2 thyristor Q2 Reset is only possible by switching off the NIM module 5 7 2 Troubleshooting ATTENTION NEVER operate the power supply with the jumpers Wl and W2 set for opposite polarities the internal circuits will be damaged Be careful when measuring some components are at ac line potential NOTE For troubleshooting do not plug the module in crate where 6V is already supplied If the module is not working check the NIM crate that proper ac input voltage nominal 117V through bin 33 and 41 is supplied Check the ac input fuse on the rear panel Replace if necessary If the output voltage has exceeded the crowbar trigger level the front panel LEDs will not light To restore operation remove the ac power inpu
157. f the Member States or organizations under whose auspices the manuscripts were produced The use in this book of particular designations of countries or territories does not imply any judgement by the publisher the IAEA as to the legal status of such countries or territories of their authorities and institutions or of the delimitation of their boundaries The mention of specific companies or of their products or brand names does not imply any endorsement or recommendation on the part of the IAEA CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 CHAPTER 5 CHAPTER 6 CHAPTER 7 CHAPTER 8 CHAPTER 9 CHAPTER 10 CHAPTER 11 CHAPTER 12 CONTENTS INTRODUCTION u S l S S NR dees ORGANIZATION OF THE LABORATORY TOOLS INSTRUMENTS ACCESSORIES COMPONENTS SKILLS TROUBLESHOOTING IN SYSTEMS a POWER SUPPLIES oc n han un a uuu bapa c hunted tesi Ze ab uba PREAMPLIFIERS AMPLIFIERS DISCRIMINATORS SINGLE CHANNEL ANALYZERS TIMING CIRCUITS TSS ea SCALERS TIMERS RATEMETERS eens e teeta tenes MULTICHANNEL ANALYZERS iiss Chapter 1 INTRODUCTION Ll Chapter 1 1 INTRODUCTION Nuclear instrumentation can be found many different institutions there are nuclear research centres universities and hospitals with their nuclear medicine diagnostic or therapy units
158. f the memory is verified to see if the result is correct The part of the RAM to be tested is selected by setting the MEMORY switch If the VERTICAL RANGE switch is set to 1048K the data pattern will appear as a ramp with a positive slope and will be changed to a ramp with a negative slope 175 Chapter 9 aha TABLE 9 1 Series 35 checksums for V 2 00 Chip Option ID Number Number Number CHECKSUM PROM TYPE A28 BASIC 9000698 5583 27128 A27 BASIC 9000698 8500 27128 A31 BASIC 900070A F89C 2716 ASO BASIC 900070A 0007 2716 All 3541 900071 0994 2716 80 3541 900071 03ED 2716 A64 3541 900071 6200 2716 A77 3541N 900072A 0994 2716 A80 3541N 900072A 03 0 2716 A64 3541N 900072A 5616 2716 A77 3541C 900073A D994 2716 3541C 900073A 03ED 2716 A64 3541C 900073A 5370 2716 A30 3543 900074A 6552 2732A A49 3543 900074A 9250 2732A A53 3551 900076A 906F 2716 A53 3552A 900077 3086 2716 A53 3553 900078A 26 2 2716 A64 3554 900079A EFEC 2716 A67 3571 900080A 1C50 2716 74 3571 900080 4170 2716 A67 3572 900081A 6E3C 2716 A67 3513 900082A 809F 2716 74 3573 900082A FE2C 2716 A67 35738 90008 9548 2716 74 35738 900083A 9063 2716 67 3574 900084 5C88 2716 A52 3575 900097 D8E1 21324 A63 3515 900097 4443 2732 64 3516 900098 9F32 2716 Chapter 9 wT w w s TABLE 9 2 Chip Numb
159. ge photomultipliers due to exposure to daylight when HV is on 11 1 4 3 Preparation of the survey meter for diagnostic procedures The instrument should be checked for nuclear safety and then for electrical safety it should enter the repair workshop only if both conditions were properly tested and documented One can save quite a lot of problems in the case of a lethal accident if it can be proved that such precautions were taken The instrument should be properly cleaned before the repair work starts because if dirt move from place to another during the repair of an ionization chamber system such instabilities might develop which are rather hard to trace later Under tropical conditions it is a good general practice to dry out the units before starting the repairs This can be done very efficiently by attaching a de humidifier to a box wardrobe etc with closely fitting doors After 48 hours most of the humidity would be removed from the instruments If you have to open the instrument you are kindly requested to make note of the following suggestions Is Remove batteries from the instrument before starting 2 Try to locate the minimum number of screws etc necessary to gain access to the inside of the instrument 3 Mark the screw etc locations with a washable marker pen in sequence as you remove them 4 Put all removed screws in a box or tray in the same sequence as the marked areas Never leave
160. hat may arise from baseline fluctuations at high counting rates and from pulse on pulse pile up Restoring a spectroscopy amplifier which has undergone a failure to within the factory guaranteed performances may be outside the reach of anybody but the designer and a few service engineers However rescuing a faulty spectroscopy amplifier and bringing it back to an acceptable working condition can be done by somebody who has clearly understood the previous troubleshooting procedures referring to elementary linear circuits Before proceeding to the repair find in the manual the block diagram of the amplifier and try to understand the functions it implements Although the spectroscopy amplifiers from the different manufacturers may differ considerably from each other the differences are usually restricted to the more advanced parts like baseline restorer pile up inspector dead time and live time monitors The basic functions still follow a well established pattern which is recognizable in the block diagram of Fig 6 22 As shown in Fig 6 22 the amplifier consists of an input section which generally includes an impedance matching buffer the pole zero adjustment network and the first differentiator The input buffer may not be provided in some spectroscopy amplifiers The input section is followed by the gain section which usually consists of three wideband feedback amplifiers with provisions for coarse and fine gain settings A signal wi
161. have changed position shape Especially in portable instruments rectilinear Scanners and other instruments of which the detector heads are moving or are exposed to mechanical shock Bad contacts in or faulty HV voltage divider or bad contacts between PMT and base Attention should be paid to capacitors at the dynodes near the anode The p metal shield has changed its properties or is dislocated in fact such a deficiency mainly influences the height of the pulse A very low AC voltage A failure in one of the LV supplies Faulty plug cable connections SPURIOUS COUNTS Take all radioactive sources away and check whether background is higher than usual If yes Check whether background pulses appear as intermittant trains of parasitic pulses If this is the case observe pulses on oscilloscope or scaler and try to detect relations between pulse trains and the switching of equipment incubators deep freezers refrigerators floor polishers workmen with drills and other machines in own or neighbouring laboratories Il 12 10 11 _7 Chapter 4 Check whether pulses are coincident with the flickering of fluorescent lamps Or with starting or running motorbikes and cars on an outside parking Unproperly filtered AC Other origins of spurious counts may be Electrostatic discharges especially in very dry laboratories HV sparking due to dust or humidity or parts starting to fail Nearby switching
162. he LO Ll and L2 addresses are increased for one Signals CCK character clock 17 and CHEN character enable ensure proper timing in data handling BOSC makes characters blink Video mixer sheet 4 DISPLAY BOARD accepts three separate TTL signals CVID NVID and IVID and mixes them into video signal VID pin 8 10 pins line connector MONITOR input use also video ground pin 10 serving for the CRT beam modulation in MONITOR The contribution of each signal in the composed signal is determined by potentiometers as follows CVID TP30 drawing characters is set by RV 5 NVID TP13 used for the normal spectrum representation is set by RV3 and IVID location A20 pin 4 used for the intensified lines like the integrated areas as set by RV4 Check also the auxiliary DC voltage at outputs 1 8 and 14 of quad operational amplifier Alll Observe signals at collectors of Q6 Q5 and Q4 They should follow the corresponding TTL input signals but the amplitude of signals depends on the RV3 RV4 and RV5 settings 201 Chapter 9 30 wd lt CURSORS Po 2 2 le JewT ie CAR Cv m VIDED vane N MIXER ane 2 r E 2 3406 I D zh Gur FER l en ays b c i FACH DIODE pu pum avg W c ou Toe 1 Ge Q3 DEA A cQ ao BurriR Sod Fig 9 33 VIDEO mixer 9 11 6 Direct Memory Access Logic and Address
163. he plug in unit differs from the one previously discussed essentially in the All input circuits To check the circuit observe the input pulse at the emitter of Q13 at test point TP6 which is the negative input of All the pulse occurs at the same time than at the emitter of Q13 and with approximately half amplitude At test point TP7 which is the positive input of All the pulse is delayed by 0 5 2 or 10us according to the delay line selected and its amplitude is reduced to about 1 3 The All timing comparator responds to the voltage difference between these two pulses changing state when the difference crosses zero before it may be seen that 1 is walk adjustment potentiometer Note that when no input pulse is present the output of All pin 5 is at logic 1 150 ISI Note 10 aboed Revenep ELN _ LAST NACE IWwTEGENTED CRINS d rs or 7 Cac TORS 4vaot en Fran TROT OTS r CIN ETTORE ama a b waq ear Se EAEE AON 9 MK x TWIST OR ari WOK ABE NO F CS BAL TNS OC mem ANC SITES ON BOT OV C ML uer MONITORS AE mised LITA TES e PB LORD AMES NOW PES Aw ON AANA Canin nj PON mn pO OAT lt lt TOS dear ATES FOOT mt CORPORAL COCA PON 2777 NOrCA 8 BEAL Aqu COMMENT KATOA hk MOC eres AME
164. he present effort to prepare a set of recommendations and tips on troubleshooting cannot replace good service manual However good service manuals are an exception as a rule service manuals are not available or are bad Therefore it is believed that the book will give valuable orientation for troubleshooting to the persons who facing a malfunctioning instrument and have no proper service manuals available The book is the product of several scientists and engineers who are closely associated with nuclear instrumentation and with the IAEA activities in the field Everybody contributed to all chapters but the responsibility to prepare the basic text was distributed in the following manner Preamplifiers Amplifiers F Manfredi Italy Scalers Timers Ratemeters J Sousa Lopes Portugal Multichannel Analyzers J Pahor Yugosalia Dedicated Instruments P Ambro Hungary Tools Instruments Accessories O Mutz IAEA Components Skills Interfaces S Hollenthoner IAEA Power Supplies H Kaufmann IAEA Preventive Maintenance P Vuister IAEA J Sousa Lopes Portugal Troubleshooting in Systems P Vuister IAEA Radiation Detectors J Dolnicar IAEA Overall editing K D Mueller FRG The organization of the meeting where the first draft of the publication was prepared and the subsequent improvement of the texts were in the hands of Mr L Kofi Ghana and Miss L Hingston IAEA Studying the book it can be n
165. he unit should be put before the detector at a given distance The readings should match with those given in the calibration certificate of the unit If this is not so one should use the STOCK FAULT LIST in section 11 5 What should you do if you have no calibration instructions or data on expected readings l If the instrument arrived without any such data and instructions you should inform the supplier and ask for replacement under the warranty 2 If the instrument has already been with you for a long time you must set up your own testing facility For this you need a small activity Cs 137 or Sr 90 radioactive source You must have information on the present activity or the source which should preferably be between 15 150kBq or according to the Radiation Safety Regulations of your area If you know the activity of the source and its distance to the detector the dose rate can be calculated with acceptable accuracy for such types of quick tests 242 a3 Chapter 11 3 The dose rate readings should match the calculated values with less than 50 difference 4 This checking however is a very rough functional one indicating only that the instrument is operating so could not substitute the calibration of the instrument in your National Metrological Institute or equivalent 5 If your instrument was recently calibrated in the National Metrological Institute it is a good practice to take readings in standardized geome
166. ibration verification of manufacturer specification modification and new developments or prototypes In the following list you will also find a Group F specially for field service This group will strongly overlap the other groups of tools but is meant for troubleshooting and maintenance away from the work bench For this purpose pre packed tool bags are available but mostly they do not fully satisfy the needs Either some items are missing or some of them will never be used Therefore it seems better to put tools used at the work bench into a bag for field service Q1 Chapter 3 22 m LIST OF TOOLS MATERIALS Room Work Benches Chairs Bench lights Trolley table Shelf Cupboard Storage cabinet Storage boxes Cabinet Screwdr vers Allen keys Pliers Diagonal cutting nippers Jewellers snips Knives Spanners Soldering units Tin different types Desoldering units Desoldering tapes different types Calipers Steel ruler Measuring Capes Punches Hammer Drills Trepanning cutters Correcut drills Drills for printed circuit boards Hand drilling machines El drilling machine with stand Stand alone drilling machine Dental drills Dental drilling machine Thread taps Die nuts threading dies Files Vices Clamps Tweezers Inspection mirrors Magnifier mirrors lenses Brushes cleaning Sprays liquids for different purposes ABC ABC ABC ABC ABC ABC ABC ABC AB
167. ices should have the same setting Speed of ports may not be set the same Big difference in baudrates Device controller or driver cir cuits may be defective Cables may not be plugged snuggly into port or may be broken Printer Possibly out of paper Printer lid if raised may inhibit further printing Computer or terminal port to which printer is attached may be incor rectly configured as DCE or DTE verify this Printer ribbon may be defective or worn out replace it Computer port driving the printer may not be enabled check address of the port 220 11 Chapter 10 Garbled or lost Terminal Port speeds may not be consistent data printer or Cable could be faulty computer Character length could be wrong Flow control may not be occurring Parity may be improperly set Cable too long or too high capacity for selected Baudrate gt max length 15 m Communication Terminal Power may be off on the device line cannot be printer or This would disable DTR pin 20 established or computer which should not allow the maintained tion to be made Device or port must be in on line mode to keep DTR on and maintain the line Duplex should be the same at each end Computer at the far end may automatically disconnect if it determines that the call is being made by an invalid user Cable between the devices may be faulty or not properly wired Improper spacing Terminal or Line feeds see if c
168. ices to a system Each system participant performs at least one of three roles CONTROLLER TALKER or LISTENER A CONTROLLER manages the bus communication primarily by directing or commanding which device TALKER is to send data to other devices or to receive data from other devices LISTENER during an operational sequence A controller can be interrupted and it can command devices to interact directly among themselves The GPIB consists of 16 lines which are grouped into three sets according to function 225 Chapter 10 16 8 lines used for data bit parallel byte serial data transfer 3 lines used for control provide a data transfer handshake compatibility with both slow and fast devices 5 lines used for general management allows initialization interrupts and special controls All instruments are connected in parallel to the bus of such a system via special cables The pin assignment and description of signals is presented below Pin No Signal Description 1 DIO 1 Data bit 1 lowest Lines are also used 2 DIO 2 Data bit 2 to transmit commands 3 DIO 3 Data bit 3 When 4 DIO 4 Data bit gt 1 data on the 13 DIO 5 Data bit 5 lines interpreted as 14 DIO 6 Data bit 6 command When ATN 0 15 DIO 7 Data bit 7 data are interpreted 16 DIO 8 Data bit 8 highest _ as data 17 REN Remote Enable will be activated when system is active 5 EOI End or Identify EOI 1 ATN 0
169. ide output pulse of this monostable pin 12 acts as a reset pulse in particular it resets the baseline latch A3a b This may be observed at pin 6 of A3 which changes from logic 1 to O soon after it is again set to l by the baseline discriminator signal Note that the discriminator is reset at the beginning of the analysis cycle not at the end The monostable also resets latch A4a b disabling the timing discriminator output pin 6 of A4 then goes from logic 1 to 0 which causes the delay monostable A7 to be triggered At the end of the delay period 0 545 monostable is triggered and its output pulse does two jobs it triggers the SCA output circuits if pins 4 and 5 of A2b are at logic 1 as they should be if the baseline latch was set by the baseline discriminator and the channel discriminator has not been triggered and it sets latch A4a b enabling All for the next analysis cycle You should also test the circuit response when the channel discriminator is triggered in this case pin 4 of gate A2b should be at log c O0 and no SCA output pulse will be generated by the A5a monostable pulse The checking procedures just described are similar to the ones that may be applied to check the logic when the crossover mode is selected In this mode the output of All pin 5 is at logic 1 when no input pulse is present Note in particular that the SCA output signal is always synchronized with the timing discriminator output and that it is de
170. ient was previously injected with another radioisotope The instrument is set incorrectly for the radioisotope used There is less absorbing medium between the source and the detector than usual a different source test tube shape the test tube has a thinner wall or is made of a different material than usual The source detector geometry has changed A wrong collimator is used The lead shield or collimator has been removed or changed in position There is a change in amplifier SCA or HV setting 10 11 12 13 14 15 16 17 18 19 20 21 22 5 Chapter 4 The AC frequency is too low in case the timer uses the AC frequency as time base Check with wristwatch The scaler has a wrong setting of the scale factor and or input polarity or the setting of input discriminator has been changed For medical laboratories the activity meter dose calibrator is faulty There are parasitic pulses spurious counts noise See section 4 7 The output pulses of the amplifier have overshoots Overshoots may be counted too Pay attention to signal reflections in long cables Overshoots may cause ghost peaks on MCA systems with a fast ADC Check signal shapes See section 4 7 The earth ng has changed or ground connections have loosened The DC power supplies are not correct LV HV The amplifier or preamplifier is faulty Check pulse shapes There is a change in pulse height or shape See
171. ignals A few of them depend again on the stretcher output signal In this way we find ourselves inside a complicated feedback system 182 11 Chapter 9 The basic idea for such troubleshooting is to isolate separate blocks by fixing the auxiliary signals ADC CONV STAB STAB EERO GAIN GAIN ZERO BASELINE MCS PHA AADV STAB OUTPUTS SA2 SA2 ADC MCS AOF RELEASE READY AADV STABTRIC PRS REJ PHA ADC BUSY tT TRMR LG Fig 9 14 Canberra 35 ADC To check the STRETCHER operation for example the STRET OFF signal must be low when the input pulse appears If it is not low we can simply push it down by grounding the STRET OFF line for a short moment However such an approach is not possible in many cases The output of a TTL circuit cannot be connected to the 5 V without causing permanent damage We will start the ADC test by applying adequate pulses to the input Pulses can come from a pulser recommended height 5 V frequency if change able the highest possible from a pulse generator the repetition rate is a few thousand per second height is approximately 5 V and the duration is a few microseconds good pulses can be produced by applying rectangular signals to the input of any nuclear spectroscopy amplifier Even the probe adjusting signal 0 3 V 1 kHz from the front plate connection of the TRIO oscilloscope is suitable such pulses are applied to the inp
172. ime clock Presetable counter 12 7415161 produces the cell clock signal 7 134 ns DTCK E Fig 9 26 Clocks CELL CK 1 wama Through the further division by counters 10 and All and using the data from ROM IM 5610 the line synchronization trigger LST is formed Passing through uni vibrator 16 74LS221 the line synchronizing signal LSYNC can be inspected at TP2 After inversion in A92 74LS37 it leaves the board as LSYNC In another binary counter group A25 A26 and 27 74LS161A all the CELCK signal is divided by 547 Under the name FST it triggers two serial connected uni vibrators in 15 7415221 The resulting signal FSYNC can be controlled at TPl The signal leaves the DISPLAY BOARD as FSYNC after the inversion in A92 Inside the CRT synchronizer unit some additional control signals like GT1 GT2 dead time meter gate CHEN character gate DGT data gate and SDMA start direct memory access are also derived As inputs to A9 ROM IM 5610 signals from VERTICAL CELL COUNTER A10 All are taken A further division of the field synchronizing signal provides a 2 1 Hz blink frequency for flashing messages There is no test point for it it appears at pin 6 A29 9 11 2 Dead Time Indicator The task of this unit schematically presented in Fig 9 27 right part is the determination of the ADC dead time and the generation of signals to sh
173. in troubleshooting between analog and digital instruments The steps of intervention required to eliminate a given trouble in analog instrumentation are described in Table 6 1 Steps a and b are carried out in the same way regardless of the nature of the faulty instruments test c has to be tailored to the actual nature of the faulty instrument though requiring a common testing structure which exists in most laboratories while d may require even purposely developed instrumentation The correct way of carrying out steps a to c will now be discussed while test d will be described with reference to the specific instruments that will be considered afterwards The analog instrument you will be required to repair or to bring back to operate within the manufacturer s specification can be either a desktop instrument with a built in power supply a rack instrument with a built in power supply or a module to be fitted into a NIM CAMAC or EUROCARD crate without built in power supplies 105 Chapter 6 7 TABLE 6 1 What to do in case of trouble STEPS TO BE TAKEN evident failure input signal mot transmitted to the a VISUAL INSPECTION output basic function no longer implemented and so forth b ANALYSIS OF dc WORKING or gt CONDITIONS obvious type of malfunctioning signal distortion excessive noise of any nature reduction in the dynamic range and so forth c INVESTIGATION OF THE SIGNAL BEHAVIOUR WITH
174. in Al4d and wired OR through this gate with the external ENABLE signal to control counting gate 45 through A45b Note that the ENABLE port may be used as an output driven by open collector gate Al4d The start signal line at the output of Ai4d is also used to keep the A35 and A34 time generator counters reset while the line is at logic 1 counting not started simultaneously it also keeps the parallel load of the down counters enabled 160 EI Chapter 8 A2e and d form a falling edge triggered monostable that starts a counting cycle through Al3a if D2 is moved to the Z position This is necessary if one wants to allow counting to start at the falling edge of the external ENABLE signal The stop signal either from the manual switch or the preset count output resets the A3 flip flop through the Al5a gate thus counting is disabled When pin 11 of Al4 goes to logic 1 the 10s monostable implemented in one half of 24 is activated if the RECYCLE mode is selected After the 10s delay the 10 us 24 monostable is triggered to clear the 51 scaler and to parallel load the 42 43 counters while the flip flop is set through A46d and Al3a This keeps the counter recycling with a 10s interval from the end of one counting period to the beginning of another 8 3 5 The Counting and Preset Circuit The preset count value takes the form pqxlO r where r is set to a value in the range O to 6 and pq is a two digit number taking
175. in this case 1 101 There might be other inconsistencies 5 6 2 1 Circuit description ATTENTION Circuit operation is described according to the diagram and does not include the modifications later introduced by the manufacturer Zener diode CR101 and operational amplifier 104 generate the 9V reference voltage The oscillator is built around IC104B The driver stage built around IC105 is coupled through C108 and C107 to the power transistors Q101 and Q102 of the push pull stage The driver stage is controlled via capacitor 104 by the oscillator and dc controlled via the amplifier bias current input by operational amplifier 1 102 This operational amplifier is itself controlled by the voltage setting operational amplifier ICIO3A The output to the voltage monitor is taken from amplifier 1 101 The over voltage detection is performed by a summing amplifier IC 103B 1 2 of CA3240 and operates in the same way as the shut down function of the inhibit gate 5 6 2 2 Troubleshooting NOTE Use the HV probe to measure the output voltage Such a probe should have a built in 1000 1 or 100 1 voltage divider Be careful when measuring high voltage 97 86 ER e am Sec ru SUETA EEMSCO 402 ES ea ju 2 a env NIGA VOLTAGE MODULE av wo sav J ovTeur REVERENCE GEME LATOR t reom gt INNIBET GATE
176. ine and introducing a variable DC voltage to R108 This way the oscillator and the power stage and the voltage multiplier can be tested separately The operational amplifier can be tested if the feedback loop is opened at A A and a variable DC voltage is injected to the junction of R202 and R206 through a 100 kOhm resistor If the voltage input is changed the output should suddenly change in the reverse direction when the operational amplifier is good The output signal from the photo multiplier is fed through junction G to the amplifier section consisting of a buffer IC 2203 a level discriminator IC 2202 and the output amplifier composed of 0201 at TP1 on the emitter of Q204 By the adjustment of the potentiometer R215 the triggering level could be set Testing of the scintillation detector is done with a small 15 150 kBq activity radioactive source preferably a Cs 137 one If the detector operates a few microseconds long a few hundred millivolt and positive amplitude signals should be observable on TP1 while the source is a few centimeters from the detector and the detector voltage etc is on 256 qoad uor3aeIII3utoOs jo SurA1IlM Sta ITT TI CARTE REGULATION I C205 81 Cw 6A Dum aw A1 n 8 aw RU BCWT0A aL Sspactre 1 1 Ce R220 mo R219 1 mn fiet LIAN Cat nf WE
177. ing the imaging it could happen that a fraction of the photopeak information will be lost On the scintigram it might look as if certain organ areas had lower metabolic functions It is easy to test the system by attaching a small radioactive source to the detector and keeping the scanner record the measured intensity in this fixed geometry A good scanner should not drift in one hour more than ten percent recorded intensity 11 2 4 3 Pulse height analyzer All recommendations given for pulse height analyzer trouble shooting are valid for the scanners as well there is however one additional uncommon stock fault 271 Chapter 11 32 Isotope selector drift Most scanners have certain preset channels for the most often used isotopes The adjusting elements might change their value due to environmental effects It is important to check the accuracy of the preset channel positions periodically by comparing the manually adjusted photopeak counting rates to the preset channel results If they differ by more than 104 readjustment is indicated 11 2 4 4 Counting rate meter The counting rate meters drive the intensity to colour code converter in the display system The linearity of the conversion is critical and since it can lead to false medical diagnosis it has to be checked periodically The procedure is rather simple One should measure the frequency of a pulse generator which drives the pulse height analyzer A graph should
178. ining of the staff is required to keep up with the extremely fast progress in the world of electronics and computer science The IAEA is developing a computer based management scheme for preventive maintenance such a system can be developed locally not necessarily computer supported can also include repair and Servicing aspects 2 4 INSTRUMENTATION AND ELECTRONICS COMPONENTS Chapter 3 provides detailed information on the type and amount of testing instruments and tools required for normal operation of a service laboratory at different levels It should be emphasized that the testing instruments ina laboratory should be regularly checked and calibrated for proper operation such controls should include connectors and cables 14 cr Chapter 2 Furthermore a certified recalibration of instruments used measurement standard at a national institution should be planned The acquisition of any instrument preferably with two sets of operator and service manuals even at additional expense should be accompanied with the provision to order some spare parts and components One set of operator and service manuals should stay at the location of each instrument while the other set should be kept in the technical library of the service laboratory good rule can be that 1 1 2 Z of the value of the instruments should be invested in spare parts at the time when the purchase 15 made In the following years each instrument wi
179. int is the battery output In most systems there is a possibility to do this checking with the built in battery tester If the DC DC converter is faulty the detector will not operate properly The second key test point is collector of the transistor driving the step up transformers primary coil The third key test point is the DC output of the DC DC converter Special care should be taken with this voltage measurement because the internal resistance of this point is rather high The fourth key point should give information on whether the detector is functioning or not The best point to check for this is the output of the first active component In the case of the ionization chamber DC level change should be present at this point if a radioactive source 15 to 150 kBq activity is moved slowly to the detector and away from it The pulse rate should change as a function of the source to detector distance in other Systems The fifth key test point should give information on the output signal of the display driver and the sixth should be the presence of the display itself There is a possibility to introduce simulated signals voltage levels to each key test point with proper care and this way one can test the functions of the circuit after that point For example instead of the batteries one can give power from a regulated power supply The same applies for the DC DC converters case if there is no detector voltage from
180. interruption When the transformer has shorted winding this appears as an overload and current limitation should take place In this case transformer Tl has to be replaced After inserting capacitor Cl3 and you observe that an overload appears again a defective component must either be in the filter capacitor C27 to C29 or in the voltage multiplier Remove one after another capacitors C27 C28 or C29 and check again If no defective component was found the next step is the inspection of the voltage multiplier When troubleshooting a voltage multiplier work carefully Measure the voltage of each multiplier stage either with a HV probe or with a static voltmeter If a stage has the same voltage level as the previous one it is defective either the diode or the capacitor Replace the defective component and check again When everything seems to be working properly you start to recalibrate the instrument Set the front panel dial to 5 00 which should correspond to 5000V and measure the output voltage With two potentiometers R22 and R15 the voltage can be adjusted R22 is responsible for the setting of the 5000V level R15 is used to adjust the low voltage region Check the linearity of the dial setting by measuring the output voltage do this slowly so that the capacitors can follow by increasing their charge With potentiometer R42 you can change the oscillator frequency which is necessary to minimize the current consump
181. is possible to distinguish if there was bad adjustment of the overvoltage protection or if a transient occurred during the switching on of the instrument 89 Chapter 5 12 w w w s w w 22222 TABLE 5 1 Typical DC Voltages measured with respect to TP1 without load in 8 3 2 5 3 9 5 5 0 5 12 0 7 0 7 12 0 2 2 5 2 9 5 1 24 0 1 0 10 23 9 10 0 2 6 725 3 6 1 4 U4 pin 8 36 5 U8 pin 8 9 5 3 2 5 3 21 5 5 0 5 24 0 7 0 7 24 0 2 2 5 2 21 5 1 12 0 1 0 10 11 8 10 0 2 6 13 5 6 13 TABLE 5 2 Pin assignment for NIM modules BIN MODULE CONNECTOR PIN ASSIGNMENTS FOR AEC STANDARD NUCLEAR INSTRUMENT MODULES PER TID 20893 Rev 4 adopted by DOE Pin Function Pin Function 1 3 volts 23 Reserved 2 3 volts 24 Reserved 3 Spare Bus 25 Reserved 4 Reserved Bus 26 Spare 5 Coaxial 27 Spare 6 Coaxial 28 24 volts 7 Coaxial 29 24 volts 8 200 voits dc 30 Spare Bus 9 Spare 31 Spare 10 6 volts 32 Spare 11 6 volts 33 117 volts ac Hot 12 Reserved Bus 34 Power Return Ground 13 Spare 35 Reset Scaler 14 Spare 736 Gate 15 Reserved 737 Reset Auxiliary 16 12 volts 38 Coaxial 17 12 volts 39 Coaxial 18 Spare Bus 40 Coaxial 1 Reserved Bus 41 117 volts Neut 20 Spare 42 High Quality Ground 21 Spare G Ground Guide Pin 22 Reserved gW
182. ited Such a short circuit may also be due to an external unwanted jumper in which case VISUAL INSPECTION 15 ADVISABLE BEFORE REPLACEMENT V BE is zero yet IE is different from zero Base and emitter are short circuited either inside or outside the device VISUAL INSPECTION IS AGAIN ADVISABLE BEFORE REPLACEMENT The resistors may also be responsible for incorrect operation of circuit actually a resistor can have changed its value because of a previous incorrect intervention on the circuit during which excessive power was dissipated owing to an accidental short circuit because of a manufacturing defect or because of strongly adverse environmental conditions 5 Chapter 6 As a limiting case a resistor can either be open circuited or short circuited Table 6 2 describes what happens in the circuits of Figs 6 1 and 6 2 with Rl or R2 either open circuited or short circuited E EE EE z 1g x x z s s 2 TABLE 6 2 Failures in the circuit of Fig 6 1 caused by resistors Rl open circuited VCE 0 VBE in normal Tl saturated range R2 open circuited Ic O O Tl off R2 short circuited E2 O 6V small and negative or positive Rl short circuited no voltage VBE in normal drop across range R1 What happens in the circuit of Fig 6 2 if R3 is open circuited is described in Table 6 3
183. iving signal for the moving coil type display meter In some advanced neutron dose rate meters the energy dependent Quality Factor weighing is done with a microprocessor and an analog to digital converter system 11 1 4 Diagnostic Procedures 11 1 4 1 Health safety hazards In all survey meters DC DC converters are used to supply the detector voltage The charge on the filtering capacitors might not be lethal in passing through the person touching it but unintentional muscle contractions might cause serious damage The diodes in high voltage power supplies are of good quality the reverse currents are rather low and due to this even after tens of minutes enough charge might remain to give painful kick All instruments arriving for repair should be carefully checked for the bleeder resistors presence having the role of automatically discharging the high voltage capacitors Survey meters are often used in areas where they might be exposed to radiological contaminations It is very important to check all units entering the workshop for this and all repair work should be done only on radiologically safe instruments 11 1 4 2 High value components safety It is very important to inform the repair staff on the proper handling and testing of the valuable hard to replace components 245 Chapter 11 6 The most often destroyed components during repair of survey meters are the following FETs due to electrical dischar
184. layed by A7 for a preset time interval relative to the All triggering time 149 Chapter 7 6 7 2 4 The Output Circuitry The output pulses from this unit are intended to actuate the inputs of coincidence plug in units or of time to amplitude converters The output circuitry should be able to drive terminated 509 cable discrete circuits are used here for this purpose You should check if the positive going pulse at the output connector J2 complies with TTL standards Actually from the circuit you should expect logic O0 to be less than 0 2V for currents as large as 50mA Q7 and Q9 are saturated Q8 is cut off and logic 1 to be higher than 2 5V for currents larger than 50mA Q7 and Q9 are cut off Q8 acts as an emitter follower The circuit for the negative going NIM pulse should sink a current of roughly 17 if this current flows through 50 Ohm resistor a signal of 0 8V develops this signal is rather narrow due to the differentiating time constant of about 20ns at the circuit s input If the discrete output circuits are suspected of malfunctioning the techniques given in Chapter 6 for the troubleshooting of transistor circuits may be followed 7 2 5 Constant Fraction Timing Discriminator Another common method of obtaining accurate time marks with a small amplitude dependent time walk is the constant fraction method A circuit example may be taken from Canberra s Model 2035A constant fraction timing SCA see Fig 7 4 T
185. le electronics laboratories advice and assistance in the topic of preventive maintenance and training Obviously a necessary prerequisite for staff responsible for servicing of nuclear instruments is the understanding of nuclear electronics In interregional regional and national courses the IAEA is training nuclear electronics staff both in basic and in advanced aspects The present book is devoted to such persons who have either received IAEA training or have studied nuclear electronics by themselves at home In preparing a book on troubleshooting of nuclear instruments one is faced with a number of problems i The technical level of the book must be properly defined it should not be too elementary but should avoid the most advanced aspects The present publication is meant for young electronics engineers who will specialize in nuclear electronics for senior technicians or for the scientists physicists chemists who are forced to maintain and repair their instruments themselves ii Nuclear instrumentation is facing a period of rapid development New instruments are appearing on the market each week It would be impossible to analyze all the electronic circuits in these modern instruments Therefore the book must mainly focus on some general features and use some specific circuits to illustrate the troubleshooting and repair procedures that will hopefully be applicable to many different types of instruments iii T
186. le did not fully reach the measuring position A wrong collimator is used particularly for a scanner The AC frequency is too high in case the timer uses the AC frequency as time base Check with wristwatch The HV setting is incorrect 71 Chapter 4 8 9 10 11 12 13 14 15 16 17 72 The settings of the amplifier have been changed There is a change in the SCA setting There is a change in the scaler threshold setting in the scale factor or input polarity The LV power supplies are faulty the HV supply is faulty The preamplifier or amplifier is faulty check pulse shapes There is a change in pulse height or shape See section 4 7 The SCA is faulty output pulse height pulse duration incorrect The scaler has an intermittent failure or is faulty The time clock is defective Check with wristwatch A broken resistor in the dynode chain a bad photomultiplier a bad optical coupling between scintillator and PM a shorted capacitor in the dynode chain THE COUNT RATE IS HIGHER THAN USUAL Possible reasons There is an extra background source detector directed to source preparation or store rooms injected patients near to detector radioactive contamination test source 15 not placed in its lead container people in neighbouring laboratories are using radioactive sources etc The patient is injected with the wrong radioisotope wrong patient wrong source The pat
187. ll need between 1 and 3 Z for replacement parts depending on the complexity and design of the instrument Each laboratory should have a basic supply of electronic components A list is presented in Chapter 3 Section 3 4 this is considered to be a minimal set of components that have to be stock in the laboratory and need to be updated regularly It is considered absolutely mandatory that a nuclear electronics laboratory have access to some local and foreign petty cash for rapid and unbureaucratic acquisition of parts and components that are or are not available on the home market This is essential for rapid turn around of repairs it is not tolerable that the staff must wait months for the appropriate approval to buy a minor electronic part and the experimenter cannot use his instrument It should be pointed out here that there is a tendency more and more often in modern electronic instrumentation to make use of hybrid analog customized digital circuits EPROMs PALs and other programmable chips to achieve higher packing densities better overall performance and to reduce production cost It will not be possible even in a very well equipped laboratory to have all these special spare parts available in a stockroom Fortunately the failure rate of such components is low These spare parts have to be ordered from the manufacturer of the instrument or its representative are not available from the semiconductor manufacturer
188. lses do not affect Q10 but draw enough current through Q9 for a logic 0 voltage to be developed at the input of NAND gate A56c Input pulses should appear at pin 8 of A56 if pin 9 is at logical 1 this level should appear if PRESET COUNTS mode is chosen if not check Al5c for logic 0 at pin 10 and A52 for logic 1 at pin 2 8 3 2 Time Generator and Time Mark Gate Check the output of the 12 MHz generator and the divide by 12 IC A33 the output of A33 is transmitted to the ck input pin 5 of A35 if gate Al3d is opened this should occur if the external GATE input is left unconnected and should stop if this input is grounded The 1 MHz output of A33 is divided by 10 by A35 giving 159 Chapter 8 216 time marks spaced by 0 015 A34 provides division by 60 producing time marks separated by 0 01 min A36 a and b together with A46c form 2 to 1 multiplexer allowing the selection of the time scale by a switch In TP8 a time mark wave should be seen of either 0 01 min or 0 015 in the PRESET 0 015 or COUNTS position A46b is the time base gate the control input of this NOR gate pin 6 is connected to the same line as the control input of the NAND event gate pin 10 of A56 thus assuring that one but only one of these gates is always open 8 3 3 Gate Control and Event Time Multiplexer The external GATE signal actuates through NOR gate A45c If the gate is closed logic 1 at pin 8 no time pulse will pass again the output
189. ltage Any deviation from the nominal output voltage causes an amplified error signal to the base of the driver transistor Each of these regulators is biased from the next higher unregulated supply line The internal reference source is about 6 9V therefore for the 6V line the voltage adjustment must be done at the non inverting input instead of the inverting input The capacitors in this circuit are used for frequency compensation The voltage drop across the current sensing resistor drives the current 82 un BF 4 e ol q O 2 86 2 o I I L 4 a 00288 fe a a eee N Bf 4029 E EE ly 019 ay cav 69 819 9v 29 98 19 19 4 98 19 gv hg Wy 5v 8 6 89 BIY gt s 19 gt gt I 919 83 Model 7021 Canberra NIM crate power supply div 9Y Chapter 5 gV 019 9V gy 29 Canberra Model 7021 NIM crate power supply 5 2 Fig 84 7 Chapter 5 limiting transistor that is biased by constant current source This constant current source is controlled by a fraction of the output voltage to achieve foldback current limiting characteristics 5 3 1 2 Negative output voltages The unregulated DC voltage is fed to the emitter of a npn power transistor its base is driven by a pnp transistor An integrated voltage regulator gives the a
190. lution After connecting the preamplifier to the main amplifier and this to the multichannel analyzer adjust the amplification of the main amplifier so that the 5 9 keV peak will be registered in channel 300 or there about Use long shaping time try to match the specification on the certificate say 16 microseconds and the amplification about 300 Make the energy calibration of the MCA using two calibration X ray sources two different pure metals on top of the holder with the excitation source One of the two should be the Fe 59 source Collect sufficient counts in the peak to obtain good Statistics Determine the FWHM of the k alpha the largest of the Fe 59 radioisotope peaks The FWHM value of the 5 9 keV peak in eV is the resolution of the detector as given in the certificate Fe 55 calibration source is available you can use excitation source and an iron sample Although the resolution is determined at 5 9 keV the Mn K alpha line the value obtained with the iron target 6 4keV for the 1 line will be a good approximation 12 1 4 3 Efficiency Determining the efficiency of the x ray detector as the function of x ray energy is a tedious and long procedure see for example the IEC Publication 759 Standard Test Procedures for Semicondictor X Ray Energy Spectrometer Around 10 keV a Si Li detector efficiency is 100 falling to zero at 2 keV and decreasing less radically on the high energy
191. ments where the detector must be inserted in a measuring chamber and the protruding preamplifier is an obstacle These detectors are somewhat more difficult to service and repair ii A widely accepted configuration is shown in Fig 12 8 Here the preamplifier is located in a separate box that is attached to the dipstick Such a preamplifier can contain the input stage with the FET at room temperature this solution is sometimes applied to the gamma ray detectors In most cases the protruding box does not contain the input stage this is somewhere inside the detector cap with the FET at low temperature Suppose that you have a gamma ray detector with a preamplifier outside the detector cap Something seems to be wrong with it Basically there are two possibe types of defects mechanical and electronic The defects and their symptoms are listed in Table 12 1 288 11 Chapter 12 N in po Fig 12 7 Streamlined detector Fig 12 8 Preamplifier preamplifier setup outside TABLE 12 1 Defects and how they are recognized a Mechanical defects the vacuum inside the moisture or ice accumulated detector cryostat is bad at the neck of the cryotat the detector is broken no signal at the output when gamma source is close the wires inside the no signal with source or detector heads are broken with pulser b Electronic faults input FET is defective no output signal with test
192. mplified error signal to the base of the driver transistor For optimum operational conditions of the error amplifier a zener diode is used for level shifting The 6V line regulator gets its power at V from the 5V line and its V from the 6V sense line The two other regulators are powered at V from common and at V from the corresponding sense line The 6V regulator s non inverting input is connected to common and the inverting input is wired to a resistor chain which is connected between the reference voltage and the sense line For the 12 and 24 voltages the reference voltage is fed to the inverting input and the non inverting input of IC2 and IC3 and gets its signal from a fraction developed between common and the corresponding sense line The negative regulated output voltage passes through a current sense resistor at the collector of the output power transistor The voltage drop is added to the auxiliary 5V voltage and a fraction of the output voltage The voltage of the matrix point drives a current limiter transistor in case of excessive load current 5 3 2 Maintenance For readjustment of output voltages and current remove the upper cover of the power supply The corresponding potentiometers for voltage and current adjustments are marked with U and I at the top of the regulation board Maximum current shall not be adjusted above 120 of nominal value To verify exact voltage measurements a separate bin connector and probe cable
193. mpling scope is available However there is a very simple trick to judge whether GHz oscillation is present simply by reading dc levels The trick is based upon the fact that the high frequency oscillation rectified by the non linearities present in active devices actually modifies the de levels in the circuit Monitor then the 112 9 Chapter 6 dc levels in the proximity of the replaced transistors and see whether or not they change by adding a small capacitance between base collector emitter of the new transistor and ground Such a capacitance will modify the ampl tude of the oscillation and along with it the dc levels To add such a capacitance just handle an ordinary screwdriver possibly long and thin and touch with its metallic top the transistor leads being careful to avoid short circuits see Fig 6 5 Fig 6 5 Testing of a transistor stage for oscillation with a screwdriver If no modifications occur in the dc levels no high frequency oscillation is present If however the dc levels change when you touch or simply approach the transistor leads with the screwdriver tip then the oscillation is present In this case the newly connected transistor can be neutralized by adding a 100 ohm resistor in series with the collector lead or the base lead and as close as possible to the transistor can The previously analyzed situations refer to elementary circuits but the methods employed can easily be extended to more
194. n the linear case is however extremely useful in introducing the basic principles Suppose that following the signal path you arrive at a circuit illustrated in Fig 6 13 with signal shapes as indicated 123 Chapter 6 20 Fig 6 13 AC coupled operational amplifier with open signal path If the circuit had previously undergone dc analysis and was found to operate correctly dc wise then the present fault that is open signal path between input and output may depend on an open C capacitor or on an interrupted connection in series with C on the printed circuit board ATTENTION Such a fault cannot be detected from the analysis of DC conditions Another frequent source of fault is a shunting capacitor which because of a mistake made in a previous repair is much larger than it should be Such a situation is illustrated in Fig 6 14 The signal actually does not appear to the output as it is Short circuited to ground by the 100nF capacitor connected by mistake The collector to ground capacitor of large value interrupts the signal path again In this case DC analysis would not reveal the fault 124 21 Chapter 6 E OUTPUT 100pF NOMINAL 100nF ACTUAL Fig 6 14 Transistor stage with defective output signal Consider now the following two transistor operational amplifier Fig 6 15 and look at the output signal a Suppose that the oscillation frequency exceeds 100 MHz Such
195. n use it should be in ts container Try to reduce exposure to yourself and to others 2 Never touch the source with your hands This even applies for the less than 37 kBq activity source 3 If you use a radioactive source do not allow smoking eating in that room 4 You should strictly follow local Radiation Safety rules wear the film badge or other personal dose meter etc The next instrument that you will need is a multimeter preferably with a minimum 20 kohm volt input resistance with proper connecting cables If you have an adjustable low voltage power supply it could be advantageous to use this instead of batteries but this is not essential It is a good practice to measure the current uptake so you should have an ammeter preferably a fused one To check the operation of the DC DC converters or the pulses from the Geiger Mueller tubes scintillation detectors an oscilloscope will be necessary with a minimum 3 MHz bandwidth and 50 mV division sensitivity A standard probe with a minimum 1 MOhm input resistance is enough for most of the tests however 1 10 range extender might ease the work With the exception of the ionization chamber system electrical pulses carry the information You can simulate these with pulses from a generator having the means to adjust the rate width and amplitude So you must have a pulse generator with maximum 10 volts of adjustable amplitude from 5 microsec to 10 msec width
196. national Electrotechnical Commission published detailed instructions for testing of semiconductor detectors For gamma ray detectors the IEC Publication 656 1979 Test Procedures for High Purity Germanium Detectors for X and Gamma Radiation can be ordered from the Bureau Central de la Commission Electrotechnique Internationale 1 rue de Varembe Geneve Suisse 12 1 3 1 Determination of resolution Resolution of a gamma ray semiconductor detector is defined as the full width at half maximum FWHM of the peak that corresponds to the gamma rays from Co 60 at the energy of 1 3MeV The measurement is simple place a suitable Co 60 calibration source at a distance of 25 mm from the face of the detector The counting rate of the detector should be at least 1000 counts s The resolution of a detector depends on the counting rate with a higher counting rate the resolution decreases The commercial companies make their measurements for the certificate at a counting rate very close to the nominal 1000 counts s Using a spectroscopy amplifier with carefully adjusted pole zero cancellation and a good multichannel analyzer collect a spectrum of Co 60 In the central channel of the 1 3 MeV peak at least 10 000 counts should be collected With a modern multichannel analyzer the FWHM can be determined by the firmware of the instrument Otherwise you can do it approximately on the monitor of the MCA precisely by plotting the part of the sp
197. ng the DMA cycle the CPU data bus is tri stated and external users have direct access to the RAM Check TP5 for Al3 by using DCHA2 as the trigger The end of the DMA cycle is indicated by DMEND signal from monostable A5 and triggered by the signal that can be observed at 205 Chapter 9 34 Until now we have talked about the ADC gain of 8291 channels Frequently we use less channels to have the possibility for registering several spectra In such cases the starting address also depends on the base address For available base addresses and their coding see Table 9 6 The current base address is kept within the miscellaneous board 0000 003F 0040 Program Read Only 16K FFF 4000 Program Program Program Bank 0 Bank 1 Bank 2 Read Only Read Only Read Only 16K 16K 16K 8000 Data Byte 1 LSB 2K 4K or BK 9FFF A000 Data Byte 2 2K 4K or BFFF C000 Data Byte 3 MSB 2K AK or 8K DFFF 000 Variables and Parameter Stack 3 75K EF7F EFBO Return Stack 128 EFFF F000 FFFF Fig 9 36 TABLE 9 6 TABLE 9 7 B B3 B2 Bl BO Base R2 Rl RO Range 0 0 0 0 0 0 0 0 256 0 0 0 0 0 256 0 0 1 512 0 0 0 1 0 512 0 1 0 1024 0 1 1 768 0 1 1 2048 0 0 1 0 0 1024 1 0 0 4096 0 1 0 0 0 2048 1 0 1 8192 0 1 1 0 0 3072 1 0 0 0 0 4096 1 1 0 0 0 6144 For a proper display the memory address should not run higher than the starting address plus the number of channels The number 206 35 Chapter 9
198. ngineering CAE facilities are envisaged an air conditioned computer room and room for work stations should be made available 2 For countries in tropical regions the laboratory should be air conditioned At least a part of the laboratory should be equipped to have a dry area i e a room with reduced humidity 3 An adequate storage room for special packing material that has to be kept for emergency return shipment should be available 4 The electronics laboratory should have a good reliable mains supply properly arranged electrical power distribution and preferably a good dedicated grounding system 5 The laboratory should have good overall illumination For precise work on electronics instruments individual working places should have additional lights 6 Depending on the size of the laboratory and its activities additional room space with reduced humidity for storage of electronic instruments and components as well as the proper 13 Chapter 2 2 laboratories for production of printed circuits should be arranged 2 3 ADMINISTRATION OF A NUCLEAR INSTRUMENTATION LABORATORY 2 3 1 Staff The proper staffing of the maintenance and service of a nuclear electronics laboratory is obviously the most important part of good management At the start of such laboratory it is advisable to make a complete inventory of all the instruments the institute or institutions that are expected to be served by the l
199. o the border of the green and red areas This test should be done once yearly BEFORE the calibration in the National Metrological Institute 11 1 6 4 Stability testing All instruments should be tested for stable operation after repairs for a minimum of six hours This test should be carried out with a regulated power supply delivering the nominal voltage expectable from the dry batteries for example 8 1 5 volts in the case of the M I P 10 survey meter The intensity should be adjusted to give an 80 deflection on the meter Readings should be taken in every half hour time and a graph should be plotted from the results If the readings change with more than 20 during the day the cause should be traced and repaired Care should be taken with the scintillation detectors during such measurements they should not be exposed to direct sunlight or to the cold air stream from an air conditioner It is good practice to monitor the temperature on the spot of the measurement Ll l 7 Preventive Maintenance 11 1 7 1 Recommended periodical check ups The batteries and the condition of the battery compartment contacts should be checked monthly The instrument should be tested under reference conditions a minimum of twice yearly 11 1 7 2 Preservation technologies Scintillation detector probes should not be exposed to over 50 degrees Centigrade because the photocathode might deteriorate Never leave the scintillation detector for example
200. ock can be acquired Item Quantity Description Cat No Resistors 1 50 Metal resistor 1800 31E710 2 50 3R32 31E760 3 50 5R90 31E778 50 6R81 31E781 5 100 1 ORO 30E100 6 100 33R2 30E150 7 100 51R1 30E168 8 100 75R0 30E184 9 100 100R 30E196 10 100 475R 30E261 11 200 1KOO 30E292 12 100 3K48 30E345 13 200 10KO 30E389 14 200 100K 30E485 15 200 1 00 582 16 50 3M90 30E645 17 50 10M0 30E695 18 1 Service Sortiment 011 27E230 19 5 Resistor 5W 0R33 62E112 20 5 0847 62 116 21 5 0868 62E118 22 5 1RO 62E124 23 3 Resistor network 10W MRI 37E900 24 3 MR2 37E905 25 3 MR3 37E910 26 3 MR4 37E919 27 20 Varistors 275VAC 1W 82E2255 28 20 150VAC 1W 82E2235 Capacitors coils 29 50 Tantal capacitor 6 8uF 16V 26D479 30 50 6 8uF 35V 26D600 G8 50 50 50 50 50 39 10uF 16V 10uF 35V 22uF 16V 22uF 35V 47uF 16V 47uF 35V Service Sortiment CCC 001 Electrolytic cap 1000uF 40V 2200uF 40V 4700uF 40V 10000uF 25V Ceramics cap 10pF 63V 100pF 63V 470pF 63V InF 63V 10nF 40V 100 50 Ceramics high vol 1 100pF 3kV 22pF 3kV 10nF 3kV LOuF 6kV Styroflex capacitor 470pF 160V 1000pF 160V 10000pF 160V HF coil 22uH l00uu Potentiometers Potentiometer 1K 4K7 22K 100K lOturn potentiometer 1K 2K 5K 10K 100K Dial Transistors and linear integrated circuits JFET 2N4416 2N4861 2N3819 2N3823 Chapter 3 26D480 26D605 27D524 27D568 270528 270572 2810810 1103
201. oftware Second without a logic analyzer you are in great difficulty Timing relations among the signals are essential and they can only be analyzed by using such an instrument So what to do if your GPIB system doesn t work and you don t have a logic analyzer Let s go step by step l Look to see if power is applied to all of your devices connected to the GPIB 2 Check if the interface cables are in good condition and plugged in correctly 3 Check the addresses to which each device in the system is set don t use the addresses twice 228 672 CONNECTOR TO SCALER TINER I 12V 126 12 119 GND 18 RATRE 117 GND 116 RCL 115 STP EE ST 5 413 BCD BCD BCD BCD A B ENABLE LSB ECOL RCE ECOL 5V 5V Q DN CIRCUIT R18 Re1 BYC gt E _ gt m lt m Sam POLL LATCH BEEN DATA Sam SEQUENCER 5 BEEN S2uscty W018N34u02 ssSyaau 103 ajajaa 122a EEE lt lt 3 91u 8tu 34 489 Fig 10 8 Block diagram of GPIB interface for Canberra counter 2071 Droa 2 9 3 se M TRANCE IVERS m A 2 tco Hm Roy Pam s 3 eco 4 m 2 7 pecco A9 z 8 reo po MES 509 TENE 38 re oo _ 558 E some l ca 3 35 MN
202. oldering Tools BC F The desoldering bit be inserted in soldering irons or soldering stations In any case the applied temperature should not too high and not too long otherwise the PC board will be destroyed This is dangerous especially on multi layer boards in this case it is better to cut the leads of the IC and remove them one by one Tin suction devices a one hand operation with 6750 SP exchangeable teflon tip length 210 190 mm 6750 XS ABC F Desoldering tapes length l 6m width 1 5 2 2 5 ABC F Desoldering tapes are used for absorbing excess solder on circuit boards A minimal quantity of mild and neutral flux is included The desoldering tape is highly absorbant 39 Chapter 3 20 3 2 LIST OF ACCESSORIES 1 Strips with banana plugs 0 5 1 1 5m 2 Alligator clips 3 Test clips for strips 4 Test clip for IC tests 5 Cable reeling units 3 2 6 Oscilloscope probes 1 10 1 1 3 2 7 Oscilloscope current probe 3 2 8 Oscilloscope HV probe 3 2 9 HV probe for multimeter 3 2 10 Shielded black box 3 2 11 BNC 50 Ohm terminator male plug 3 2 12 BNC 50 Ohm attenuator 1 3 6 10 10 10 20 dB 3 2 13 BNC T type 3 2 14 BNC I type male 3 2 15 BNC I type female 3 2 16 MHV T type 3 2 17 MHV I type female 3 2 18 SHV T type 3 2 19 SHV I type female 3 2 20 SHV MHV adaptor 3 2 21 BNC 50 Ohm cables 0 3 0 5 1 2 amp m length 3 2 22 SHV 5 cables 2 4m
203. olution x ray spectrometry From the outside there is only essential observable difference compared to the gamma ray Ge detectors on the top of the detector cap we find a berillium window It represents a barrier that separates the vacuum inside the detector from the atmospheric pressure outside and does not permit light to fall on the detector It does not stop x rays appreciably except if they are of very low energy say below 4 keV A newly received x ray detector should be tested for its performance immediately upon arrival After cooling it with the liquid nitrogen for several hours the tests can start 12 1 4 1 Connections and initial tests The x ray solid state detectors use two types of preamplifier with resistive feedback or with optical feedback Most of the contemporary Si Li detectors use the optical feedback because this permits them to obtain better resolution The one honourable exception are the detectors produced by ORTEC using resistive feedback Let us consider the case of a preamplifier with optical feedback After connecting the high voltage SHV connectors usually RG59 cable observe the polarity in most cases a negative voltage is applied use cable to display the output sometimes called ENERGY from the preamplifier in an oscilloscope Before the high voltage is applied the oscilloscope try to use the amplification on the vertical scale that gives 5 V cm and a time constant of th
204. ompo nents in ntegra tor loop locate replace check replace replace replace decontaminate locate bad capacitor C102 C212 C208 replace C209 replace locate repair dry system locate remove open source if possible Readjust or locate cause and repair replace replace repair or replace repair or replace replace locate repair or replace locate replace 23 Chapter 11 Alarm system not bad 2202 replace functioning bad Z100 2 2 or replace C111 R115 bad Q106 or loud speaker 11 1 6 Quality Control of the Repaired Instrument The repaired instrument should be tested with the reference Source of the workshop in a standardized geometry that is the same distance between the detector and source and same relative position A simple approach is to mark on plywood the outline of the detector and the location of the source with its identification number During all measurements this set up should be used It is very important to record the results and to compare them to previous tests It is good practice to record the power uptake of the unit during tests which helps later on with diagnosis An increasing current uptake compared to previous measurements could be the sign of an insulation deterioration due to moisture accumulation in the DC DC converter transformer In an early stage often a simple drying might save the instrument from a total breakdown During the reference measurements
205. omputer out Double spacing printer puts a line feed with each carriage return If so option for zero line feeds at the device or option the computer to only output a carriage return No spacing Terminal or Computer is only outputting a printer carriage return while the device is not adding a line feed Option either the computer or the device to add a line feed with each carriage return If you look with an oscilloscope to the transmitted or received signals don t expect very fast leading or trailing edges 10 4 PARALLEL INTERFACE CENTRONICS This type of interface is mostly used to connect printers to a PC Synchronization is done by STROBE pulses supplied the transmitting device in our case the PC Handshaking takes place through ACKNLG or BUSY signals Data and all interface control signals are compatible with TTL level Both the rise and fall times of each signal must be less than 0 2 us As to the wiring for the interface be sure to use twisted pair cable for each signal and never fail to complete connection on the Return side To prevent noise effectively these cables should be shielded and connected to the chassis of the host computer and the printer 221 Chapter 10 12 respectively Interface cables should be kept as short as possible to avoid problems max length m Most of the input and output drivers are very sensitive against connecting devices together while power is applied They may be damaged
206. onnections Mechanical vibrations of dynodes in PMT rectilinear scanners Chapter 5 POWER SUPPLIES Chapter 5 5 POWER SUPPLIES 5 1 GENERAL REMARKS Before starting to discuss troubleshooting for specific power supplies some general comments and some hints for troubleshooting are given The discussion some specific power supplies is presented in Sections 5 3 through 5 7 There are two main types of power supplies The linear regulated supplies with power transformer rectifiers capacitor filtering pass transistor current sense resistor for current limitation either for constant current or with foldback characteristics and the error amplifier including the voltage reference source rectifying filtering fast switching power transistors ferrit core transformer for power transfer fast switching rectifier diodes filters with chokes and capacitors current sense resistor for current limitation either for constant current or foldback characteristic regulator with pulse width modulation including voltage reference source and in the feedback loop either an opto coupler or a pulse transformer The switched mode power supply with direct ac line The first step in troubleshooting is visual check looking for burned components If the instrument smells or if smoke is coming out there is obviously something wrong inside Try to find out which part of
207. or and source distance is critical in imaging the best resolution could be obtained from the focal plane of the multihole diaphragm before the scintillator The optimal imaging distance is given on the diaphragm Each scanner has some means for the detector positioning This function is used during the setting up adjustment By looking the counting rate meter or listening to a variable frequency loudspeaker sound controlled by the radiation intensity the operator should search for the area with maximum isotope concentration This manual mode can be used to test the safety switches on the border of the maximum scannable area If the detector is not stopped there automatically the drive mechanism can be harmed A block schematic of a typical scanner can be found in Fig 11 16 11 2 4 Troubleshooting and Stock Faults 11 2 4 1 Power supplies In most systems separate low voltage regulated power supplies are used for the nuclear channel and for the detector motors A DC DC converter feeds the scintillation detector which receives power from the nuclear channels voltage regulator The trouble shooting procedure is similar to all scintillation detector high voltage power supplies 269 mmm WSINVHOGW ss 4 ugauoogy ALISNSLNI 2800 TIOD usonqsNvur NOILISOd UTLINMAGAL l SONSHSIJSM e I o YOLOW OANS3S WO IOD 5 2
208. or high voltage transients are present on the supply lines This often happens in hospitals where the cables are heavily overloaded and the wire connections are corroded An AC voltage stabilizer can improve the situation for the scanner There is only one simple rule in power diode replacement the symmetry should be conserved in the rectifier that is if the same diode which failed is not available both diodes should be replaced with properly rated ones 11 2 4 2 Scintillation detector All troubleshooting recommendations given for scintillation detectors in this manual are valid for the detectors of the scanners as well But there are certain stock faults which are not common in other applications Detector cable They are exposed to cylical bendings and movements after accomplishment of each scanning line this can amount to 10 000 cycles week and two million cycles year Most cables are worn out in 3 4 years The cable deterioration is slow sometimes noises appear without any apparent reason only in certain areas of the scintigram even without any isotope If such effect appears it is a sure sign that the cable is deteriorating Contamination of the detector Under clinical conditions it could happen that the detector surface is contaminated by the patient This can be prevented by enclosing the detector in an easily replaceable plastic sheet or bag Scintillation detector stability If the gain of the photomultiplier changes dur
209. or spare parts 3 1 10 Cabinet with drawers shelves suitable for files documents and manuals lockable 7 lt Chapter 3 3 1 11 SCREWDRIVERS Hints for selection a The shank should be made of a special alloy chromium etc better than nickel plated Layer shanks are not so handy but more universal For bigger sizes its profile should be hexagonal to give additional torque with a spanner b The tip should be specially hardened the two planes of the blade have to be parallel in the slot of the screw c The handle should be of special plastic preferably hammer hit proof Hits on the end of the handle are only allowed if the shank goes fully through the handle precaution no isolation length mm bit profile mm 60 100 shank 0 4x2 5 ABC F ee JUNEXS 005 shank 0 6x4 BC F 125 shank 0 8x5 5 ABC F 170 shank 1 6x8 BC F lt 170 shank 1 6 10 BC 200 shank 2 2 BC t 25 shank l x 6 BC 60 shank PZD 0 t 80 shank PZD ABC 150 shank PZD 3 ABC F rzj aoe 100 shank 0 9x 5 C F 100 shank PZD 1 2 F 27 Chapter 3 8 A 1 watchmakers screwdrivers set of 0 25 0 8 up to 0 6x3 8 mm B553 set of 2 Philips 0 1 mm and 3 Hex 1 5 2 5 mm _ eO LQ Sp pum ma i n s tester screwdriver split blade holding screwdriver 200 mm long 4 mm blade
210. osed manually or signal levels and or pulses Debouncing of manual switches is mandatory the corresponding circuitry is easily checked and the same is true for the latches associated with pulse control These bistable elements are easily triggered by very short pulses this may a cause of trouble if decoupling is ineffective or if glitches are allowed to occur and are not filtered out 8 1 5 The Counting Stages The counter generally provides several counting decades whose output is available in BCD format Normally only the first faster decade or decades directly associated with some types of preset control are of the synchronous type Frequently ICs with two decades are used but LSI circuits with four or six decades are already present in various instruments Preset count is frequently limited to the combination pqxlO r where p q and r represent decimal numbers Generally it involves either a comparison of the BCD coded numbers and q with the contents of the sealer or the zero detection in a count down process of two decades previously loaded with contents p and q Troubles may easily arise from glitches or spikes in the power lines 156 3 Chapter 8 8 1 6 Display Circuits Seven segment digits implemented in LED or LCD arrays are generally used in displays In LED displays two multiplexed buses are typical one from the decades to the BCD to 7 segment decoder another from the decoder to the digits In LCD
211. oted that there are different approaches and different styles used in individual sections This is in part the consequence of the fact that each chapter was drafted by a different person but it also reflects the observation that various parts of nuclear electronics require different ways of presentation For this reason no particular effort was taken to present all the chapters of the book in a uniform style All the persons who contributed to the first edition of the troubleshooting manual are well aware that the book needs further improvement In the jargon of the electronics experts we request the users of the book for a fast positive feedback that will enable us to improve the text make it more readable and understandable for the engineers scientists and technicians to whom it is intended The troubleshooting and repair of instruments is illustrated by some real examples The circuit diagrams and service manuals of ORTEC CANBERRA and NARDEAUX instruments were selected for this purpose Obviously the choice of these instruments was made only for training purposes and has no relevance to the Agency s preferences for particular brands of nuclear instruments EDITORIAL NOTE In preparing this material for the press staff of the International Atomic Energy Agency have mounted and paginated the original manuscripts and given some attention to presentation The views expressed do not necessarily reflect those of the governments o
212. ould be drawn so that the main sequence of cause to effect goes from left to right and or from top to bottom The input should always be on the left and the output on the right When this is impractical the direction of operation should be shown by an arrow Components associated with each operational stage should be grouped together Unfortunately really good circuit diagrams are still rare It is often said that the after sales policy of the manufacturer is mirrored in the diagrams Some companies prefer to give repair services and they distribute almost useless circuit diagrams to scare away non factory approaches to maintenance The standardization of the graphic symbols for components is much more efficient however some companies still use their own local standards in the nuclear field The same applies to cable connection notations and markings There is no general rule each company has its own graphic symbols in multi sheet diagrams for interconnections test points etc During repair work correct reading of the graphic symbols is essential This should be tested very carefully even a single mistake in identifying the symbols indicates further learning requirements The next step is to test ones colour code reading capabilities For efficient repair work one should acquire a faultless reading capability with a rate of ten items per minute Colour blindness inhibits the correct identification of resistor values This can b
213. ould decrease After removing the load the nominal output voltage should come back again After completing this procedure you can install all removed boards and the display unit Make sure the MCA is now working If aot see Chapter 9 MULTICHANNEL ANALYZER 5 6 DETECTOR BIAS SUPPLIES In this section bias supplies for detectors are described We can distinguish between several types of such supplies i High voltage supplies which are designed for scintillation detectors must be very stable in respect to output voltage and relatively powerful up to 1 2mA at about 2000V noise and ripple is not so critical ii High voltage supplies which are designed for solid state detectors should have low noise and ripple but are not required to be highly stable with respect to output voltage The current required for detectors such as Si Li pure Ge or Ge Li is in the order of less than 100nA Surface barrier detectors sometimes require a higher current of up to 2uA at relatively low voltage of about 100V 93 Chapter 5 16 NOTE For troubleshooting a high voltage instrument is recommended This is tance using a HV probe with built in voltage divider 1000 1 or 100 1 or either a digital voltmeter with lOMohm input resis static voltmeter 5 6 1 Example 1 ORTEC Model 459 Fig 5 6 shows a circuit diagram of a HV bias supply for a solid state detector This HV supply can deliver up to
214. ounts each channel has to be three bytes long The four highest bits of the third byte not used for channel content provide the information about the special treatment for this channel bit 21 if set the corresponding point is intensified bit 22 if set the bar is displayed instead of the point bie 23 if set indicates the channel with the biggest content bit 24 if set channel is within the region of interest 208 Chapter 10 INTERFACES 1 Chapter 10 10 INTERFACES 10 1 GENERAL All information delivered in the following chapters assumes some basic knowledge of interfaces and of Personal Computers PC It is devoted entirely to problems you will be faced with when selecting interfaces or working with them The three major groups of interfaces which will be covered are i Standard Interface Used for Data Communication the serial interface RS232 C V24 the parallel interface Centronics 11 Standard Interface Used for Remote Control of Instruments the IEC 625 IEEE 488 GPIB interface iii Non Standard Interface for Remote Control of Peripherals I O ports Motor control 10 2 SELECTION OF INTERFACE Whenever you have to select an interface ask yourself a few questions a What is available at my laboratory b Who is going to be the controller master of my system Is it a PC Is it a special dedicated device which only provides data like a multichannel analyzer MCA scaler timer
215. ow can be made high by joining the corresponding gate output to 5V However by short circuiting the emitter and collector of transistor Q29 the same effect is achieved The command to start conversion i e to inject the discharging current into Cll is given by the discriminator Al6 when the input signal has decreased to 90 of its amplitude Two additional tricks used during the conversion to improve accuracy will be described When constant current generator is connected to discharge the storing capacitor the resulting ramp voltage might deviate from linearity because of the transient phenomena Therefore counting starts later The lost time is compensated for by counting longer Counting is stopped by the zero crossing discriminator which is actually set about 80 mV below the zero level Instead of introducing the time delay T before counting we can count from the very beginning but setting the counter to the adequate negative value N Then after Nx clock period T the counter will be at zero The loading which is different for different conversion rates is realized through the parallel input of counters The second trick is the use of the so called sliding scale Because of the interference of the surrounding digital circuits the produced ramp voltage might be modulated This would result in spectra deformation The idea is to use in successive measurements different parts of the ramp voltage Therefore the binary 185
216. ow the result on the CRT screen The circuit measuring the percentage of the dead time and helping to present it is given in sheet 8 DISPLAY BOARD 196 25 Chapter 9 DICK MZEN 373040 Cru Coce Gm fae ny AP CK YRT Cok cn UNE CYR 00v10 ae uo 347 aw f 2 236 29 4 a as 48 44 S 5 ro d iwe move D smo 6 MSE 111 roa i009 DT Yw A 8 cx DEAD TWAE Cow TP LATEN zt PALS ary r 9090 craton wor PROM Danang Oe ROMY VELY 58 8 m 2 1 2 Sraer WAT SCREEN O uat DAR Obb AYEw 9715 e FELO vac Cuan Gart DATA t ches 44 GATS Tear roto Fig 9 27 Synchronizers and timers Cell clock CELCK TP7 is counted in the decade counter A30 during the intervals when ADC is busy For adequate gating the LT signal coming from the ADC board is used A97 pin 13 The counting proceeds dual binary counters A29 and A31 Collect time of subsequent runs are two frame periods which amount to 58 8 ms In this way 4096 counts are collected each time if the ADC would be busy all the time i e if the dead time percentage is 100 Only the most significant 6 digits of the obtained result are used for the indication If the dead time is smaller the number of the collected counts is proportionally smaller The obtained re
217. particular position of the COARSE GAIN knob determine the gain The resistive network which determines the COARSE GAIN in that particular GAIN setting might be badly soldered even disconnected b If the COARSE GAIN setting reveals no defects keep t fixed in a given position and rotate the fine gain potentiometer throughout its range Make sure that no sudden jumps dc level variations appear at the preamplifier output Otherwise concentrate your attention on the fine gain potentiometer and possibly proceed to change it C Check whether or not all the positions of the time constant controlling knob perform their function by leaving the shape and amplitude unchanged and by simply modifying the width of the signal d Check the presence of the signal at the bipolar output and repeat on it checks a b and c If instead upon application of the input square wave no signal appears at the output pull your amplifier out of the NIM BIN and put it open on the desk by powering it through an extending cable Increase the amplitude of the input square wave to about l100mV and follow its path through the gain section by looking with a lx probe at the input and at the output of the subsequent gain stages If the signal is present at the input of a gain stage and is no longer present at the output stop the signal analysis and after switching off the generator proceed to dc analysis of that particular gain stage Check whether
218. pear before the transceivers if not your controller is faulty For further diagnostic tips see Table 10 4 TABLE 10 4 List of problems typical for a GPIB interface Symptom Cause Remedy Device receives wrong commands transmits One or more datalines wrong results or status information NRFD NDAC interrupted cannot be addressed or tied too low bad bus transceiver Controller doesn t receive Service Request SRQ interrupted Continuously receives Service Request SRQ tied too low Device cannot be programmed ATN interrupted Device cannot receive commands ATN tied too low No remote control REN interrupted No parallel poll possible EOI interrupted Cancels receiving after first received EOI tied too low data block Bus blocked DAV interrupted 10 6 I O PORTS Most microcomputers incorporate some form of parallel input output PIO facility While an increasing number of microprocessors provide this as a built in facility parallel 1 0 invariably takes the form of one or more LSI devices known as a peripheral interface adaptor PIA Such devices generally provide separate 8 bit ports in which 8 bit lines can be configured under software control as input or output The interface from the PIA to the CPU usually consists of eight data lines two or more address lines and different control lines like Chip Select CS Read RD and Write WR The data lines are of course bidirectional whereas the address and control 232
219. per end of the range RV6 should be adjusted so that the output voltage of A9 is 5V If the circuit is not working properly follow the procedures described in Chapter 6 Preamplifiers Amplifiers to identify the fault The channel window comparison level is established by A8 which is wired as an amplifier of gain 2 the gain may be changed through the adjustment of RV2 by 2 Trim pot RVI adjusts the offset voltage as in the circuit around A9 The voltage the non inverting input pin 3 is very approximately given by VCE AE thus at the output of the voltage is 2 V E V E AE You can see that the circuit around 8 allows one to move the channel up and down by adjusting the baseline helipot without changing its width To check the circuit first set the baseline and channel helipots to zero check if the input pin 3 and the output are at the same voltage if not adjust RV1 Then turn the baseline helipot full scale the output of A9 should have 5V you should measure 45V on the output of otherwise adjust RV2 Next turn the channel helipot to full scale and the E range switch S2 to the 10V position with the baseline helipot at zero you should read 5V at the output of AB otherwise adjust RV3 Next with the same settings but with the range switch S2 in the lV position you should observe 0 5V at the output of A8 otherwise adjust RV4 The above measurements should be done carefully the corres
220. place all with the same type 11 2 RECTILINEAR SCANNER 11 2 1 Field of Application Medical rectilinear Scanners are used to map up the distribution of radioactive tracers that were introduced into the body for diagnostic purposes The output information from the scanner is the scintigram a one by one image of the investigated organ with colour coded representation of the local radioisotope concentration The areas with highest radioactive isotope concentrations are displayed with red iso intensity areas in most system 8 12 different intensity levels could be visualized by this imaging technology The pictures are used to evaluate the extent of the organ tissues participating in the normal metabolism and the locations of the already damaged areas The scintigrams are used in diagnosis in therapy planning and therapy evaluation This imaging technology is non invasive and very important because it can provide information on such soft tissue organs which could not be easily accessed by x ray or ultra sound 11 2 2 Operating Principle In the medical scanners one or more nuclear detectors are moved on a meander path above and sometimes under the investigated 265 Chapter 11 26 organ The nuclear detector or detectors are in special lead shields with apertures in the direction of the isotope distribution providing high directional sensitivity see Fig 11 13 Single channel pulse height analyzers are connected to
221. plied the detector about dissatisfactory performance of their detector be sure about your electronics setup grounding and overall conditions in your laboratory For example high humidity in the laboratory can easily deteriorate the resolution of a Ge detector that needs 5000V as the bias voltage 280 3 Chapter 12 Section 6 DETECTOR SPECIFICATIONS AND PERFORMANCE DATA REAR ENVELOPE 6 1 SPECIFICATIONS Serial Number b 86151 The purchase specifications and therefore the warranted performance of this detector are as follows Model 7229P 7500 1320 Rel Efficiency 13 Resolution 2 0 keV IME keV FWN at 1 33 MeV keV FWRI FWD 122 keV Peak Compton 1 Cryostat Description Vertical dipstick type 7500 6 2 PHYSICAL PERFORMANCE DATA Date Actual performance of this detector when tested is given below Geometry Coaxial one open end closed end facing window Diameter 48 nm Length 35 nm Active area facing window 18 1 cm Distance fram window 5 nm ELECTRICAL CHARACTERISTICS Depletion Voltage 4000 Vdc Recommended Bias Voltage 4500 Vde Leakage Current at Recommended Bias 01 nA Preamplifier Test Point Voltage at Recammended Bias 2299 Vdc RESOLUTION AND EFFICIENCY EWEMCKeV FWIM CkeV A l measurements performed at 4 microseconds shaping time Fig 12 1 The certificate for a Si Li x ray detector 281 Chapter 12 4 LI2 1 3 Germanium Gamma Ray Detector The Inter
222. ponding adjustments if necessary should be made in the stated order We now refer to the level setting for the timing discriminator A11 This level is derived from the baseline voltage follower R16 connects the output of A9 to the base of emitter follower 017 and to the ideal diode made up around 10 The non inverting input of 10 is at about 200mV pin 2 of 10 should have the same voltage if the feedback loop around the amplifier is closed This will be so if diode D3 is conducting a condition that is fulfilled whenever the output of A9 is above the value imposed at pin 3 of AlO by the R14 R15 divider network 200mV You can check for the correct behaviour of this ideal diode by looking at the anode of D3 while the baseline helipot is increased from zero while the output of A9 is below 200mV A10 is saturated output positive above this value AlO enters the active region and the voltage at the anode of D3 is clamped to the 200mV value Emitter follower Q17 drives this voltage to the timing comparator input if the leading edge triggering mode is selected However if the crossover mode is selected this level setting circuitry is not used the comparison level is then set at a value equal to the 146 291 304 Ne E wO in 7 2 Circuit diagram of a TSCA IC MICE Cot 7 0 00 vr mz LE 3T lt 950 41 C 4o s Cote
223. ppear at the output when you apply a signal at the input and are the shape and the amplitude of the output signal reasonable b If the instrument is a single channel analyzer does the logic output signal appear at the output when you apply an input signal and slowly move the threshold positioning potentiometer until the input signal falls into the channel If the instrument is time to amplitude converter does a ramp signal appear at the output when you apply a signal at the START input and a delayed one at the STOP input d If the instrument is a linear gate is the signal applied at the analog input transmitted almost unaltered to the output during those intervals when it overlaps in time with the gating command applied at the LOGIC INPUT Some situations are summarized in Fig 6 12 For each instrument there is an approximate indication of the correct and of a possible defective output signal If the signal is acceptable you can go on with a detailed analysis and calibration of the instrument If the signal is strange it is necessary to carry with a signal analysis of the individual stages To apply signal analysis you must send a signal to the input and then follow its path throughout the instrument making sure that every circuit performs on the signal the correct function Signal analysis will tell you some very important facts l The signal is present at the input of a certain circuit and is no longer presen
224. pprox 2 min Bit temperature 380 420 Weight without lead 95 g with plastic rest Voltages 6 V 12 V 24V 42V 48V 110 120V 125 135 V 220 V 225 235 V 240 250 V Wattage 80W Heating up time 3 min Bit temperature 410 C Weight without lead 220 g Voltages 12 V 24 V 42 V 48V 110 120 V 125 135 V 220 V 225 235 V 240 250 V Order nos 080 JK Iron with copper bit bits pannes Kupfer copper Cuivre ERSADUR 052 BD Holders A 11 A 12 080 JD Iron with ERSADUR long life bit ABC Kupfer ERSADUR copper cuivre ABC ABC 35 Chapter 3 16 3 1 18 Soldering desoldering station Lotspitzen bits pannes ERSADUR This electronic temperature regulated soldering and desoldering station is especially designed for industrial use laboratories and repair works The modular system permits a large field of applications The single elements can be used in individual combinations Because of a built in vacuum pump the efficient station is independent of an air pressure connection In addition the basic station contains a power supply of 220V 24V which fits all 24V soldering irons and desoldering irons up to 80W rating An electronic control unit permits continuous variation of the soldering bit temperature between 150 and 400 degrees C By means of a thermocouple sensor located in the soldering iron next to the 36 zj ja Chapte
225. r 11 15 np 0 e qe eA WACG641X78 totu voijejn6sy 3428j Jn35 1 J8AU0 241 probe Circuit diagram of a G M 11 10 Fig 255 Chapter 11 16 The Geiger Mueller tube signals should never be checked on the tube itself because the capacitive load of the test probe increases the peak current and reduces the expected life span of the tube A suitable point is on C201 If the tube is not functioning the sonde can be tested further with a pulse generator from C201 vi The scintillation detector probe The circuit diagram of this probe is illustrated in Fig 11 11 The high voltage DC DC converter is on the upper half of the drawing An audio frequency oscillator composed of three NOR circuits drives the base of Q102 The step up transformer Tl is in the collector circuit of 0102 which is fed by the emitter follower 0101 On the secondary side of the step up transformer a ten stage voltage multiplier operates delivering approximately 1000 volts if 10 volts are present on the base of the Q101 emitter follower The feedback loop is closed through the 100 MOhm value R201 resistor driving the inverting input of the 7201 operational amplifier which is connected to the base of the 0101 emitter follower Dangerously high voltage can develop in the circuit if the 100 MOhm R201 resistor is broken It is easy to test the circuit by breaking the B B connecting l
226. r 3 bit the electronic control measures the actual temperature and compares it to the nominal temperature setting By means of an integrated zero voltage switch with full wave logic and Triac the temperature is electronically controlled and the operational state is indicated by a pilot light Depending on the temperature difference or heat requirement the sensitive electronic unit controls the heating energy input in accordance with the operational state idling load The soldering bit and desoldering bit is connected to the level potential terminal via an integrated high Ohm resistor The small soldering iron is very efficient thanks to its ceramic heating element which has a pronounced positive temperature coefficient PTC and 80 Watts rating at 350 degrees C The desoldering system consists of the iron on which a desoldering head is mounted The transparent solder chamber can be emptied simply and quickly The necessary vacuum impulse for desoldering is released by a foot switch The following picture gives an overview of an extendable solder desolder station of one of the leading manufacturers i war Neuzspoannuno mans Grundgerat staton No 803 I BELL f i ungeregeiter Lotkoiben m 24 V bis 80 W Lotkoiben 24 V bis BO W unrequiated ron reguiated in the handle Ps h 24 V up to 80 W 24 V upto BOW D E am elektronische Regeleinheit elektronisch
227. r part of the screen For this task the display board is instructed which letter should be sent to MONITOR through the character video line CVID Also the dead time determination runs in parallel Data about the analog to digital converter activity obtained from the ADC unit in analog form are converted into the digital one The result is put on the internal data bus The dead time indicator scale pattern is also taken from the ROM as a separate contribution to the screen picture Data from different sources are composed together into the video signal which is used for the CRT beam modulation The display board containing more than 100 integrated circuits is too complex to be presented here even in block diagram form Therefore the partial block diagrams will be given the following chapters 9 11 1 CRT Synchronizer The final product of the CRT synchronizer is FSYNC and LSYNC signals However auxiliary signals defining the writing across selected parts of the screen like GT2 CHEN and others also generated See Fig 9 25 for the screen structure 195 Chapter 9 24 LOGO DT METER JL Gn JL GRAPHIC FIELD Fig 9 25 Screen fields pL RAS AE IPR TLD REE p CRT DISPLAY REF 6 All signals are derived from the basic clock of 14 90 MHz generated by the crystal oscillator After the division by two the DTCK signal Fig 9 26 available at TP6 is obtained dead t
228. r time In this way a bright point appears the CRT screen at the position whose height is proportional to the number of counts stored in the channel The signal A B generated in the same digital comparator tells when the number of the stored counts is smaller than the current LINE RESOLUTION COUNTER content The A gt B signal can be used to bright the bar between zero line and the spectrum point when th s is required Check the graphic field contribution to the video display at TP13 Notice to realize the overlap function the 4 bit adder A70 74LS283 and the comparators A52 A53 are used To achieve this mode a constant offset of 64 is added to RAM contents This results in a second graphic display 25 lifted 9 11 4 Status Register and Data Video Status information is needed to provide the display logic with system variables such as vertical scale expand range etc Therefore at the end of each monitor frame an interrupt is introduced through the line RST 7 5 Programme jumps to sub routine updating the status register Related schematics are at sheet 5 The block diagram is shown in Fig 9 29 Inside the display board its own data address bus is created The three state buffer 100 takes data from BADO to BAD lines and repeats them as ADO to AD7 Enable of A100 is controlled by CHEN A10 1 or pin 19 Lines A8 to 15 are reproduced at outputs of A80 also the three state output buffer Three lines
229. reached Nevertheless replace your FET following the recommendations below so you will not keep the PA out of use In the meantime order a specimen closer to the one which was originally put in your instrument 6 2 1 3 Replacement recommendations 1 Deduce from the circuit diagram of the PA the value of the standing drain current ID 2 If ID ids near or below 10 mA then stick to a FET of the 2N4416 type This type should be available n your laboratory Select the which features the highest gm value circu t 21 b among those rather than have IDSS values between 10 and 12 mA 3 If ID is above 10 mA typically 20 to 30 mA make your selection among FETs of the 2N4861A type Remember incidentally that a very reliable manufacturer of FETs for low noise is INTERFET 322 Gold Street Garland Texas 75042 USA You can ask for their catalogue and determine their equivalents of 2N4416 and 2N4861A 132 29 Chapter 6 More complicated is the selection when the PA employs two paralleled FETs and one or both have to be replaced Although one FET may have survived this can be useless for it may be very difficult to match it without having components of the same type or even not knowing the type Proceed to group out of your batch of either type depending on the standing current they worked at the pairs of FETs that have IDSS close in value Then parallel these pairs and measure the gm of the parallel combination Next selec
230. red equipment is kept in boxes sometimes for years This is not tolerable and the electronics laboratory can contribute to the action upon delivery each instrument should be immediately unpacked inspected for possible damage and all claims should be submitted as soon as possible otherwise the warranty might be lost installed and tested A document should be prepared specifying the measured properties of the instrument later this will permit a comparison on the instrument s performance For every instrument a logbook and repair list should be opened at the time of its arrival All subsequent actions be it for preventive maintenance or repair of the nstrument should be registered in this book The head of the workshop should set a good example on the utilization of the logbooks otherwise it will not be used by the personnel It is highly recommended to start weekly repair case discussions and to use the logbook during this session It is advisable for the repair of an instrument to be organized in the following way a copy of the circuit diagram should be made and the values obtained in measuring the quantities such as DC voltage and signal shape should be registered Such an updated diagram should be stored in the logbook If no diagrams are available a careful record should be maintained of the measured values at selected points of the circuit The staff of nuclear electronics laboratories should learn from their mi
231. ress Latch Enable is used to load the low byte address to the external latch 8085 needs a clock therefore an external clock signal of 6 MHz is applied to Xl while X2 is left floating The CPU board has a 12 MHz A43 oscillator divided down to 6 MHz in 74150292 44 The buffered 6 MHz is the clock input to the 8085 The 8085 also divides this clock by two and outputs it as CLK signal To execute an instruction the 8085 divides the operation into machine cycles An instruction might take from one to five machine cycles In each machine cycle there are three to six time states T see Fig 9 16 Each T state consists of one clock period The activity of 8085 within each machine cycle is T1 Output an address T2 Switch A D from address to data IN OUT T3 Hold data stable T4 T5 Internal operating time for 8085 eae AD wR M3 OPCOPE FETCH MEMORY READ MEMORY WAITE Fig 9 16 8085 timing What is going on in the processor can be learned from status signals RESET IN sets the programme counter to zero and resets all flags it initializes the microprocessor RESET OUT indicates that CPU is being reset This signal can serve as the system reset 187 Chapter 9 16 RD WR The behaviour is evident from Fig 9 16 The shown pulses are sent out HOLD input when driven high _tri states the address and data lines as well as RD WR and IO M line Internal processing can continue HLDA is
232. roe Sw 3 MONT vat MEAG Ab Com more TIERE ARE Q KOM rr TED ON FAS KARAT NE paano TROSG 400 w lt lt 3 OC mien PONT ON 002 lt ATES sapa POR ELDAD lt O NOKA AN On PONE Caw An 6 O lt Cs Am SPP WNACAIES ALOT AN COMPONENT COCA TO a C NORM CS REAR AVE COMPONENT LOCATIONS Orc FUS CD em O P IICATES MOLITE CAP 1 3dey9 Chapter 7 4 average voltage of the input line that is at the mean value of the output of the amplifier connected to the present instrument see Fig 7 3 7 2 2 Analog Input and Discriminator Circuits The input analog signal is divided by 2 before it is applied to the comparators A6a channel and A6b baseline The input is dc connected and a first check can be made by applying a dc voltage to the input For example if the baseline helipot is set at half scale position the comparator should trip when the input voltage is approximately 5V The hysteresis of the comparator is fixed at roughly 5mV by the resistor network R26 R9 This may be checked by verifying that the voltage at pin 9 of A6b takes values differing 5mV from each other according to whether the output of the comparator is at logic 0 OV or at logic 1 5V The comparator inputs are protected by diodes Dl and D2 and also by the circuit around Q15 which does not allow the input differential voltage to exceed the limits specified for
233. rt of the cryostat Clean them preferably with methane but at least with a dry and clean cotton buds Pay special attention to the high voltage filter in the preamplifier usually made of two highohmic resistors and two high voltage capacitors The test input on the preamplifier box is connected to the detector crystal via the high voltage supply lead Using a pulser or a pulse generator you can inject the signals through the detector diode to the FET If there are signals on the output of the preamplifier you can conclude that the FET is working and that the high voltage lead to the detector crystal is not interrupted If the x or gamma rays are still not detectable you can conclude with a high probability that the detector itself is faulty NOTE Modern high resolution semiconductor detectors are good and reliable instruments If operated with proper care they will last for many years Even the old detectors can be trusted fifteen year old Ge Li detectors that still operate with full original specifications are not unusual In most cases it is a human error that kills detector Handle these detectors with care and you will not need the above troubleshooting advice 291
234. rter In most instruments voltage muliplier circuits are used If there is no DC output on the last stage of the multiplier it is worthwhile to test the other stages because often only the last diode fails Typical DC DC converter output voltages are the following ionization chambers 200 600 volts Geiger Mueller tubes 350 1200 volts scintillation detectors 600 1000 volts semiconductor detectors 60 400 volts When the internal resistance of the converters is in the 100 kOhm 1 MOhm range the readings on a low internal impedance voltmeter will be correspondingly lower so care should be taken in their evaluation On the fourth test point a DC level change is expected if the intens ty of the radiation changes In all other systems pulses should be present on this output if the detector and the first stage operates n response to the radiation The signals from a Geiger Mueller tube are many microseconds long while the scintillator signals are only some microseconds in width The amplitudes range from a few tens of millivolts to volts If the fifth test point is the output of a counting rate meter a DC level change should be the response when the radioactive source to detector distance is changed The deflection of the moving coil meter should change in the same way If a digital display is used in the survey meter the checking should follow the instructions given in the scaler section of this manual 11 1 4 8
235. s used to turn on and turn off the instrument battery checking is the first position after the switched off state control the measuring range selection Some designs have ZERO SETTING and CALIBRATION controls as well je ao ao cC on PROBE 6 9 Y Le Fig 11 1 Front panel of a typical radiation monitor 241 Chapter 11 2 In ore prospecting the use of energy selective measuring channels is rather common The front panel of a typical survey meter with a scintillation detector is shown in Fig 11 2 ISOTOPE SELECTOR ENERGY WINDOW iue T F EGG GOOD MANUAL O PRESET CRM RANGE MODE SWITCH ON O TEST OFF uGy h Fig 11 2 Front panel of a typical survey meter Controls for the energy and the intensity range setting are common with the single channel analyzers The radiation intensity can be read from either a moving coil meter or a digital display The first step of the quick functional test is the same for both design variants the instrument should be turned into the battery checking position The indication should be BATTERY OK or similar If this is not so one should use the STOCK FAULT LIST given in section 11 5 If the BATTERY OK condition was indicated the second step can be started by following the calibration nstructions of the manual adjusting the controls to the appropriate ranges after the instrument was zeroed Then the cal brating radioactive source of t
236. s of all the operator manuals Originals of all available service manuals circuit digrams parts lists and troubleshooting information A set of data books on electronic components as minimum it is recommended to have a set of D A T A Books D A T A Inc P O Box 26875 San Diego California 92126 USA possibly complemented with some publications of individual producers of electronic components application notes referring to nuclear electronics from instrument manufacturers catalogues 2 5 ORGANIZATION OF THE WORK IN AN ELECTRONICS LABORATORY Frequently a nuclear electronics laboratory combines its activities in service with some deveiopment work in order to give its staff a chance to keep up with the rapid development in nuclear electronics In such cases the basic rule should be The repair and servicing of instruments has priority to other activity of the laboratory The electronics laboratory should be involved in a research instrument from the moment of its delivery A staff member should assist in the unpacking installation and initial testing of every newly acquired instrument For those instruments that cannot be repaired locally and where there is a possibility for them to be sent for repair special shipment material should be stored 16 e Chapter 2 In laboratories and institutes in developing countries we frequently observe the wooden box effect the delive
237. s the sum of all switches in the ON position DON T select an address already used in your system Also address 31 is illegal it is reserved for the GPIB command UNTALK The sixth switch is TALK ONLY At this point you have to decide whether your scaler works with or without a controller The TALK ONLY mode is used to transfer data from a single module to a single peripheral listener device such as a GPIB printer If the TALK ONLY switch is off the controller must assert REN REMOTE ENABLE during the entire communication The seventh switch is RECYCLE In the ON position the unit will clear after readout and start counting again In the OFF position the unit is in the single cycle mode 227 Chapter 10 18 The eighth switch is FF CR In the FF position the message unit delimiter is sent out as an ASCII Form Feed In the CR position it is sent out as a Carriage Return The choice of the delimiter depends upon the peripheral device being used Let us take closer look at the interaction with a controller A typical counting sequence would begin with the operator pressing start on the Counter After reaching preset the Counter will generate a SRQ Service Request via ECOL END COLLECT from counter timer The controller would then via Serial Poll determine the device requiring readout During this polling sequence the controller will assign each of the devices to be polled a Talk address and then the device will p
238. s to be applied During the melting tine the heat capacity of the solder tip has to be sufficient not to drop the temperature beyond the liquid region of the solder Why not take a soldering iron with temperature far above the melting region The followibg observations speak against such a procedure 32 13 Chapter 3 Sensitive components cables connectors printed circuits etc will be destroyed if they are exposed too long to higher temperatures The temperature of the solder should drop into the solid state very fast because movement of the parts in liquid or paste condition will cause a bad contact cold solder point Considering the previous adequate soldering tools have to be selected XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 33 Chapter 3 14 3 1 18 Soldering irons and bits Wattage 8W Heating up time ca 90s Bit temperature 290 C Weight without lead 26 g Sr with rubber rest Voltages 6 V 110 V 130 V 220 V 240 V BC 1AC Order nos 230 LN 8 W Iron with nickel plated copper bit 230 LD 8 W Iron with ERSADUR long life bit Wattage 15 W Heating up time ca 60s 230 15 Watt Bit temperature 350 Weight without lead 28 g with rubber rest E Voltages 6 V 12 V 24 V 42 V 48 V 110 V 130 V 220 V 240 V Order nos BC 230 LN 15 Wiron with nickel plated copper bit 230 LD 15 Wiron with ERSADUR long life bit Watt
239. scillators it is easy to understand that the load can only change about 1 10 otherwise the oscillator would be matched This is true for example for computers where the load changes are small and load regulation not critical The recovery time is about 3 5 msec For nuclear applications such a long recovery time could be critical if a supply voltage is used for a reference purpose A module for NIM crate is available EG amp G Model 495 to supply an additional 6V line either positive or negative switchable if this voltage is missing in the crate Fig 5 8 shows the circuit of this module Such a module can be used to supply the digital logic of an ADC which is now produced as a NIM module 99 001 Circuit diagram of the EG amp G module 495 it emt gt gt SEE HERE mi MOIST tenuia aig je Gem a 208101024 GAL isos Canon A 2648101026 mAAL D s tree 1h Caretiten venus ls nicho ONE ram icette Tl Ponta vom wau of fuls Connes Can b OF MB ot 98 80 E pity BORD Anar 210 00 01 4 aaadeug 23 Chapter 5 Sua Circuit Diagram Description The regulation is done by a single pulse width modulating integrated circuit Ul This IC is powered by transformer T3 rectified by bridge D6 and filtering capacitor C The ac power is rectified by bridge Dl filt
240. screws just on the table 25 If you have to remove many screws and there is no space to do proper markings make sketches It is a justified question Why should one put so much energy into such a simple routine activity It could happen that you will be able to continue this very repair only months from now it could be that you will remember all screw positions their lengths in different locations etc but what happens if you don t It could happen that somebody else might finish the job because you were promoted or something You will find it worthwhile in the long run to follow the given suggestions 246 afe Chapter 11 11 1 4 4 Recommended test instruments It is a statistically proven fact that 35 of the faults in survey meters could be located with visual inspection smelling and touching Please try to rely on your senses before you start using sophisticated instruments The first item needed in survey meter repairs is the radioactive test source This should be matched to the nature of the survey meter For example if you have to repair a neutron dose rate meter you must have access to a neutron source during some phase of your work but please remember that all nuclear detector signals can also be simulated by electrical or electronic means It is important that users of radioactive sources should be trained on proper handling and storage of these The simple rules are the following l If the source is not i
241. section 4 7 The SCA is faulty The scaler s defective The timer is defective There is a light leak in the PMT and or the canning of the detector resulting in extra pulses in the low energy part of the spectra and peak widening THE PULSE HEIGHT IS LOWER OR HIGHER THAN USUAL Possible reasons are Without change in pulse shape Incorrect radioactive source Incorrect HV setting Incorrect amplifier settings amplification factor pulse polarity The detector assembly has been interchanged The amplification factor of the preamplifier has been changed A channel shift or wrong setting of the SCA this question comes up only when no oscilloscope is used 73 Chapter 4 6 7 10 11 12 13 14 15 16 17 18 19 74 The detector is broken or yellow brown this cannot be checked for an integral line assembly A bad optical joint between the detector and the PMT this cannot be checked for an integral line assembly A HV supply failure With change pulse shape rise time fall time over and undershoots Incorrect setting of differentiation and integration time of the amplifier The pulse height and or shape at the output of the preamplifier has changed A faulty pulse shaping amplifier The ground connection to the detector canning is loosened or interrupted or in general a change in earthing The PMT is faulty or has changed its characteristics The dynodes may
242. side 285 Chapter 12 8 12 1 5 Maintenance of High Resolution Detectors In addition to all the established routines for the proper handling of nuclear instruments some specific precautions should be applied to the solid state detectors that operate at low temperatures All modern high resolution solid state detectors can be stored at room temperature In your laboratory you might still have an old Ge Li detector or a Si Li manufactured before 1982 These detectors have to be kept at a low temperature at all times How do we know when the level of the liquid nitrogen the dewar is too low One can buy some level measuring devices or as an electronics man you can design one yourself More simple is to put the dewar with the detector on a bathroom scale and determine how heavy the system is with and without liquid nitrogen In many laboratories the dewar is refilled by a rather dangerous procedure of taking the detector from the dewar filling the liquid nitrogen by pouring it in the dewar and reinstalling the detector If you are a very careful and rather strong man this technique works But it is much more advisable practical and safe to acquire a transport dewar with a filling attachment see Fig 12 5 a LN EXHAUST VS gt gt T d PRESSURE ETE RELIEF DRY ROGEN PRESSURIZATION INLET AN i nc Z RK 2 Z gt J Se g FOAM INSULATED FILL HOSE
243. stable within 30 500 cm min range The detector in the lead shield is over 60 kgs in most designs so a powerful motor system is needed to move it line wise and step wise The line direction is perpendicular to the spinal chord in some systems they call it the X axis and the step direction as the Y axis Scanning is a series of information gathering processes which is rather slow Taking one view often requires over 20 minutes but less time is needed to complete the scintigram if the scanned area is smaller The programming of the scanning area is done with the LIMIT SWITCHes on the X and Y axis After completion of each line detected by the LIMIT SWITCH a step wise detector motion takes place and the line scanning direction is reversed It is important to know that if the activity administered to the patient is greater the scanning time is shorter Another important feature of the technique is that if the patient moves during the imaging the picture will be blurred and then it should be repeated If the channel is not on the photo peak the image will have poor geometrical resolution with low diagnostic value 266 Chapter 11 WSNNVOS JHL SNITTSAT I 5301545 S IOHLNOO ISNNVHO HV3 IOMN 27 SNINOILISOd MNOLOSL3Q 304 IONLNOO S IOHLNOO H3NNVOS LNSILVd WVHOILNIOS gee He ea SAIUG GNV WALIYMa
244. stablish the block diagram of the instrument and to identify the faulty block or blocks This is generally easy for an absolute signal failure but may be rather tricky for the faults related to degraded performance spurious counts erroneous preset counting etc 8 2 1 Checks at the Component Level First check whether power arrives at the appropriate pin of the 1 The truth table of gates must be seen to be followed otherwise the component is defective A check should be made to verify if the voltage levels are well within the legal limits for 157 Chapter 8 4 the inputs and the outputs this applies to all digital circuits In latches and flip flops check if the Q and Q outputs are in fact complementary in general check the truth table of the component If the component is supposed to behave in a dynamic way like a LSI counter with multiplexed output verify whether the scanning and related signals are being sent out Analog comparators and transistors are sometimes found especially in input and output circuitry Measurement of the voltage levels at the input and output will generally show whether a comparator is working properly Transistors are easily checked as discussed elsewhere frequently they will be either on or off and the voltage levels they give to the following circuits should be seen to comply with the appropriate legal levels under the load conditions in which they are expected to operate Displ
245. stakes The staff member of the electronics laboratory who is expected to repair a faulty instrument should make inquiries on how the fault has developed This might require an adequate approach some careful not inquisitory investigation and should preferably be made by senior person The findings should be recorded in the logbook Preventive maintenance is described in Chapter 13 17 Chapter 3 TOOLS INSTRUMENTS ACCESSORIES COMPONENTS SKILLS L Chapter 3 3 TOOLS INSTRUMENTS ACCESSORIES COMPONENTS SKILLS Tools are needed for proper maintenance of instruments The number of tools however is very large even if only a certain category of service work let us say troubleshooting of nuclear instruments has to be performed The following compilation of tools shall give an idea of what is needed at a work bench or in the laboratory The discussions on the appropriate tools and instruments will distinguish between different levels of troubleshooting Accordingly the following list of tools will be divided into three groups Group A necessary as a minimum to solve simpler troubleshooting and maintenance tasks e g cleaning replacing of simple components yes or no tests Group B for advanced repair work e g in addition to A replacement or repair of more complex components like multiple step switches hybrid circuits connectors moving coil instruments etc Group C for sophisticated repair work e g cal
246. sulting number stored in latch A32 is compared with the six lower bits LO Ll L2 L3 14 and L5 of HORIZONTAL LINE COUNTER in the 6 bit digital comparator A33 A31 The result of comparison A34 pin 7 tells which of both numbers is bigger If this signal would be used for the CRT beam intensification then the pattern of 8 vertical bright raws would be seen over the full screen The width of the raws would be dead time dependent but the full screen is taken for presentation Additional logic is introduced to limit the picture size The pattern is activated only in the sixth row by applying L6 17 and L8 to the gate A28 The height is defined by the signal derived in the CRT SYNCHRONIZER applied to the same gate 197 Chapter 9 26 9 11 3 Data Point Video During the scanning of the display field the properly timed burst signals are required to draw the pattern One of these beam intensifying signals makes the picture of the spectrum within the graphic field It is produced inside the data point video section sheet 2 and 3 of the DISPLAY BOARD documentation Start at sheet 2 and find the local bus lines ADO to AD7 From the local data bus 20 bit data about the memory content are locked in A86 A88 and A89 at O to 1 transition of the BYTICLC TP29 BYT2CLC TP24 and BYT3CLC TP25 For further processing only 8 of 20 bits are selected because of the limited display possibilities Fig 9 28 A Len ap
247. t Therefore for any precise determination which is time consuming their amplitude should be stored This is done by using the special unit STRETCHER The form of the obtained pulse is given in Fig 9 9 Such operation can be realized by using the circuit given in Fig 9 10 However its properties not adequate The real stretcher has incorporated more than 20 20 transistors anda few integrated circuits Now the pulse is properly formed Shall we start the measurement Let us be sure that the peak is over For this we wait that the instantaneous pulse value drops below 90 of its peak value which is stored in the capacitor A discriminator comparing 90Z of the stored voltage with the instantaneous signal value will tell us the right moment Fig 9 10 to start The height determination starts using the circuit shown in Fig 9 13 When the constant current is applied to the capacitor the voltage on it starts to go linearly to the zero Fig 9 11 During discharging we count one two three Counting is stopped when zero voltage is reached The counting result is proportional to the pulse height The analog to digital conversion has been performed Really No the conversion procedure was over simplified There are a lot of tricks to squeeze out the 1 8000 accuracy using the analog computing technique The signals in the typical ADC unit have to pass through more than 80 integrated circuits and 50 transistors CONSTANT CUR
248. t the pair with the highest gm Once your selection is made it would be better to check the condition of transistors Q3 Q5 Q Q6 anyway just to make sure that your accurately selected FET s once put on the circuit won t be damaged because of the charge sensitive loop Only f Q3 Q5 Q4 Q6 are in good condition introduce the FET s you have selected Now the charge sensitive loop should be in the correct de condition Consider now the case in which being VD positive of some volts VA is much lower than Vl which shows that the FET is in a good state if so the failure is likely to have occurred in Q2 Q3 Q4 Apply the already explained dc analysis to these transistors one at a time following the recommendations of section 6 1 3 Once you make the necessary replacements check again the de conditions of the charge sensitive loop Once this is fixed you can go ahead by testing the dc condition of the output amplifier Measure voltages at points E G H L after removing R8 Point out that VE must be close to VF and that VG must be near OV Besides the current flowing across R19 5 mV splits in almost equal parts between Q7 and Q8 that is about 2 5 mA in each transistor 2 5 mA will then flow across R9 thus keeping VH to about 17 7V VL must be about 7 V more positive If the voltages VE VF VG VH VL differ considerably from the stated values and especially if VG is positive or negative of some volts then the outpu
249. t amplifier is defective To troubleshoot it first of all check the output stage and determine whether or not current flows across R24 and R26 The presence of current across R24 and R26 tells you that 010 and 0911 are alive If it is so focus your attention on 07 Q8 Q9 Disconnect jumper AC AB in which case you open the feedback loop and you can check the behaviour of 07 Q8 in the open loop situation Disconnect Q9 and make sure that the currents across Q7 Q8 are not very different from each other or at least that none of them are at zero In this way you check the condition of Q7 Q8 If required replace the defective component Check then with the transistor tester Q9 and if necessary replace it Then again connect Q9 and reintroduce the jumper The dc condition of the output amplifier should now be correct Consequently the whole preamplifier should now be order from the dc standpoint and you can proceed to signal analysis 133 Chapter 6 30 6 2 2 Troubleshooting of Spectroscopy Amplifiers Modern spectroscopy amplifiers have reached a high level of sophistication as dictated by the need of ensuring advanced performances in terms of resolution counting rate capabilities and fast recovery from heavy overload To meet the demand arising from high resolution spectroscopy a considerable improvement has been introduced on the built in base line restorers and pile up rejectors in order to avoid spectral distortions t
250. t at the output The circuit under test has an interruption on the signal path 2 The signal appears at the output of an amplifier clipped on the top although the input was in the correct range The circuit dynamic range is out of the specified value 3 The signal passing through a linear amplifier appears at the output smeared by an oscillation whose frequency exceeds 100 MHz You can almost be sure that in the circuit there is an ill neutralized transistor 121 Chapter 6 18 MATE PULSE Wu sms RATE 100 ME aneurents our Accarrahe carer gt Ne feere beraecnva PitganfuritA perectwe A Anss vons tpn Rawr t e jok He 1 AQEPTANE eon dows n o PAM NOLAND Rast SePurueq Y x Aast wrom i IOONS OT cm de UNGAR Care To THe store Fig 6 12 Test set up for some typical nuclear electronic instruments with acceptable and defective output signals 122 NOTE To carry on signal analysis you meed a rectangular 19 Chapter 6 The signal passing through a linear feedback amplifier presents at the output a damped oscillatory behaviour Most probably the feedback loop is not sufficiently compensated A linear feedback amplifier whose function is that of amplifying and not that of shaping slows do
251. t from the module and then turn it on again If the instrument still does not work remove the load and try again When this does not work remove jumper between transistor Ql and transformer Tl Now measure the voltage across C4 about 16V If there is no voltage remove IC Ul and check by measuring the supply path 101 Chapter 5 24 transformer T3 rectifier bridge D6 and capacitor C4 If voltage is present the defective IC has to be replaced The next step is to check with the oscilloscope if trigger pulses are coming out from the output of the IC If not check the voltage drop across resistor R5 It should be near zero otherwise IC Ul is defective and has to be replaced ATTENTION With the next steps you enter into this is where line potential occurs REMOVE the grounding lead from oscilloscope probe to prevent a short circuit from a mains phase via oscilloscope earth ground As the next step check whether pulses appear at the gate of power MOS FET QI If not check the path capacitor 14 transformer T2 resistors R2 R9 and clipping zener diodes D4 D5 If everything is OK insert the jumper which connects transistor Ql and transformer Tl Now check with the oscilloscope at this jumper if pulses occur due to current limitation being activated this could be prevented Therefore the voltage drop across resistor R5 has to be monitored Under normal conditions there should be only a small voltage
252. t should be replaced 43 Chapter 3 24 List of instruments For analog troubleshooting and development 3 3 1 AVO meter 3 342 Digital multimeter 3 3 2a handheld 4 1 2 digit 3 3 2b bench model 4 1 2 digit 3 3 2c bench model 6 1 2 digit 3 3 3 Capacity Inductivity meter 3 3 4 Transistor tester 3 3 5 Insulation tester 3 3 6 Oscilloscopes 3 3 6a portable up to 20 MHz 3 3 6b bench type up to 40 MHz 3 3 6c bench type up to 100 MHz 3 3 6d storage type 3 3 7 Pulse generators 3 3 8a double pulse generator 3 3 8b precision pulse generator 3 3 8c sliding pulse generator 8 DC power supplies 9 Transistor curve tracer 10 DC current meter current probe 11 Noise RMS meter 12 Complete equipment for spectroscopy For digital troubleshooting and development 3 3 13 Logic tester probe 3 3 14 Signal injector 3 3 15 Digital circuit tester troubleshooter kit 3 3 16 Break out box 3 3 17 IC tester 3 3 18 Logic analyzer 3 3 19 Prom programmer 3 3 20 In circuit emulator with terminal or PC 3 3 21 Development system with printer 3 3 22 Experimental computer board single board computer 44 ABC ABC BC ABC ABC BC BC BC BC ABC BC BC BC BC C 25 Chapter 3 3 3 1 AVO Meter Analog instrument with fast overload protection internal battery 1 5V for resistance measurements similar types for higher current ranges are also available Specifications Vde O 1
253. tage REMEMBER RS 232 output levels for LOGIC O SPACE between 5V to 15V LOGIC 1 MARK between 5V to 15V RS 232 input levels for LOGIC O SPACE between 3V to 15V LOGIC 1 MARK between 3V to 15V INPUTS are ENABLED when positive DISABLED when negative OUTPUTS are ASSERTED when positive FALSE when negative We will ascertain the SEX of the computer first If the PC is a DTE device pin 2 should be the transmitter and its negative voltage will illuminate the green LED The receiver terminal if left unconnected may illuminate an LED if a pull up resistor is present If pin 20 Data Terminal Ready or pin 4 Request Send is on the port is more likely emulating Data Terminal Equipment and is expecting to be connected to a modem or a device emulating DCE signals On the other hand if the display shows that signals such as Clear To Send pin 5 Data Set Ready pin 6 or Data Carrier Detect pin 8 are present the port is probably emulating DCE and will allow a straight through cable to be used when connecting a terminal configured as DTE as if connecting to a modem If you don t have a break out box the levels can also be determined by an oscilloscope or a DVM If you want you can build up a LED Voltage Detector by yourself to test your interface pin by pin Fig 10 1 215 Chapter 10 6 Red LED Green LED 470 ohm RED BLACK Fig 10 1 Simple LED voltage detector To avoid confusion
254. tage of the error amplifier should be 1 2 1 4V higher than the corresponding output voltage line If this voltage is much higher one of the following transistors is defective because they are used as voltage follower In this way a defective component can be easily detected If the IC output does not show the mentioned voltage value and the voltage between pin 10 and pin 1 is not higher than 0 4V check the input voltages and compare them with the output voltages if there is any discrepancy replace the IC If the voltage drop is higher the fault might be either a defective shunt resistor R46 R60 R74 depending on which line the fault occurs or at the current limiting circuitry Measure the voltages around the constant current source transistor base emitter collector of transistor T4 T6 T8 depending on which line the fault occurs For the negative supply lines proceed as follows the output voltage of the error amplifier measured after the zener diode should be about 0 5V negative compared to the corresponding output voltage If this voltage is more negative one of the next following transistors are defective If the output voltage measured after zener diode does not have the nominal voltage value check the input voltages of the IC and compare them with the output If any discrepancy is found replace the IC At the node of the zener diode and the collector of the limiting transistor a voltage is developed by the current sum over a
255. te check with an ohmmeter that no short circuit exists between the supply voltage inputs and ground the rear connection If no short circuit is present connect it to the crate supply through a flat cable or through an extension and turn power ON Check on the module under repair whether the correct supply voltages appear at the relevant points 2 If a short circuit is detected from either resistance measurement supply voltage measurement at the relevant points in the instrument repeat the visual inspection following the power supply wire where the short circuit exists If the visual inspection remains unsuccessful remove one at a time the filtering capacitors connected between the power supply and ground and repeatedly check whether the short circuit still exists or not Most likely the short circuit is due to one of these filtering capacitors 3 Once the possible short circuits are removed and the correct dc supplies appear on the relevant lines measure the dc levels inside the instrument by using a digital voltmeter with least 3 1 2 digit resolution and 10 M or more input resistance MAKE SURE THAT ONE INPUT OF THE VOLTMETER IS SAFELY GROUNDED SOLDER ON THE TIP OF ITS LIVE PROBE 10K RESISTOR Such a resistor has a decoupling purpose and avoids the situation where the relatively large input capacitance of the voltmeter connected between the emitter of high frequency transistor and ground make it oscillate 6 1 3
256. ted computer labels appear on the USART Note that this interface works with without the control protocol since the input handshake lines are pulled up Most of the interfaces work in this way So you only need to define pins 2 and 3 But don t forget to connect the ground pins 1 and 7 Fig 10 3 shows the widely used TTL to RS 232 converters The receiver includes a hysteresis input to reduce its noise sensitivity The supply voltage for the 1488 does not have to be symmetric Positive voltage can range from 7V to 15V and the negative from 3 to 15v b RECEIVERS 04 0 23 input hystereols e ORIVER 469 MCI488 Qued evt put current llaillaq MCI488A Quad 1 lapul hysiroela Fig 10 3 Pin out of RS 232 drivers and receivers As a typical example we will take the interface board of a MCA 35 from Canberra Fig 10 4 shows you the circuit diagram where A69 is the USART 57 is the transmitter and A67 is the receiver One typical example is to connect a MCA like Canberra 35 to a PC in our case an IBM compatible The MCA is set as DCE the PC as a DTE In this case you can use a cable which is connected straight through PC Pin Pin TD 2 gt 2 RD RD 3 lt 3 TD CTS 5 5 DTR DSR 6 lt 6 DSR gt pulled to 5V through DCD 8 lt 8 DCD j 218 ric a K t al _ tg pe bs sss
257. th short risetime is usually taken from the first amplifier of the gain section and sent to a fast channel The fast channel shapes the incoming signal to a narrow width a few tens of nanoseconds and through a threshold discriminator provides the triggering signal for the PILE UP REJECTOR The fast channel is an auxiliary signal path which has the purpose of enabling the PILE UP REJECTOR to detect couples of events coming too closely spaced in time The main signal path from the output of the GAIN SECTION goes to the shaping section which in most cases consists of two second order differentia tors The signal it provides is unipolar nearly gaussian in shape and its path goes through the baseline restorer to the UNIPOLAR SIGNAL OUTPUT An alternative path through the second differentiator provides bipolar output available at the relevant connector 134 S14 70 9 WeABETP xoorq 3 rIjIlIdue Adoosoaqoeads GAIN SECTION COARSE GAIN SETTING FINE GAIN ADJUSTMENT I H 1 TU S ERIS EDU CEN DUXI INPUT SECTION INPUT BUFFER INPUT 1 NOT EXISTING IN GAIN i GAIN i i GAIN SOME AMPLIFIERS STAGE RUE ar STAGE smog 2 ADJUSTMENT 157 DIFFERENTIA rt m 3 ur TION SS E MEE J I 1 i I I 1 i T Ore FIRST SECOND AN INTEGRA
258. the connections in the plug all right Is the power cable all right 4 Are the fuses on the instrument all right and DC 5 Are the DC power supplies all right 70 Chapter 4 Are the signal lamps faulty THE INSTRUMENT DOES NOT COUNT To be checked Is the test scaler in test function Is the HV switched on and connected to the detector Is the input polarity of the amplifier correctly set Has the threshold of the SCA been set to maximum or the window to 0 Are the DC fuses all right Are the DC supplies correct Check voltages of HV and LV Are all signal cables alright Check the presence of signals at the output or preamplifier the input and output of the amplifier the input and output of the SCA and at the input of the scaler Check whether the plugs are correctly mounted e g the pin a male BNC may be moving backwards when connected to the socket Are the cables connected to correct inputs and outputs THE COUNT RATE IS LOWER THAN USUAL Possible reasons There is no radioactive source in the measuring position or a wrong source a wrong patient sample a patient wrongly injected The instrument is set incorrectly for the radioisotope used There is more absorbing medium between source and detector than usual different source test tube shapes or the test tube has thicker walls is made of material other than what is usual The source detector geometry has changed or the samp
259. the heatsink These locations are exposed to the ac line voltage 88 li Chapter 5 In Table 5 1 the typical dc voltages measured with respect to or ground are given which should be very helpful for troubleshooting The pin assignments for the NIM connector are presented in Table 5 2 5 5 MCA POWER SUPPLY From the circuit diagram Fig 5 4 it is difficult to realize that the 24V line is the dominant supply voltage From this voltage all others are derived by using the 24V either as reference voltage or by supplying it to the operational amplifiers which are used to generate the various voltages This 24V line is controlled by a overheating sensor switch and appears only if the temperature of the heatsink at the back panel is below the critical value In the 24V line regulation circuit there is a zener diode It is used to provide the regulated 24V as the reference voltage for the operational amplifier This circuit reduces the influence of the line variations to the output voltage At all other supply voltages the regulation is implemented in a classical way using operational amplifier and current limitation with foldback characteristic Only the 5V supply uses two parallel power transistors because a high current has to be delivered In addition it is necessary to protect the digital ICs from overvoltage an overvoltage protection circuit is introduced After power is switched on 5 LEDs indicate the following
260. the scope on the position of highest vertical sensitivity possibly 2 to 5 mV cm use ac coupling in the scope trigger the scope on AUTOMATIC turn on power on PA and look at the output baseline If the output baseline looks to be smeared by noise Fig 6 19 then your is likely to be in a correct de condition 128 25 Chapter 6 VA a ee NOISY LINE NOISE FREE LINE a b Fig 6 19 Output baseline of a preamplifier as seen on a Scope In this case you can go on by sending a signal to the test input and see whether according to Fig 6 12 the output signal is acceptable or badly distorted In the former case your PA has successfully passed the simplest test and most likely it requires more sophisticated and specific procedures If instead the output signal looks to be badly distorted or unexisting at all you must carry on a complete troubleshooting procedure Open the PA box and start with dc analysis Returning to the output baseline displayed on the oscilloscope if it is not smeared at all by noise then the PA is saturated somewhere Again in this case a complete troubleshooting procedure has to be carried out starting from dc analysis To illustrate the above consideration on the example of a commercial product let us consider the CANBERRA 2004 preamplifier with its circuitry shown in Fig 6 20 The charge sensitive loop consists of JFET Ql of the long tailed pair 02 Q3 non inverting gain stag
261. the transistor has been disconnected The troubleshooting procedure for voltage divider consists of checking whether VB is either equal to El or to E2 In the former case Rl is short circuited or the B through R2 to E2 line is interrupted Short circuit and interruption may actually reside on the printed circuit board in which case accurate visual inspection may lead to their detection Otherwise they have to be attributed to Rl or R2 or to both Replace both resistors Check VB again and you will see that now VB is at its nominal value Having the transistor disconnected check it with a curve tracer a self constructed tester or with a commercial transistor fixture and decide whether to replace it or not Check R3 and R4 and decide accordingly whether they be kept or must be replaced Finally reassemble the circuit and check VB VE VC again The flow chart summarizing the described troubleshooting procedure is given in Fig 6 9 117 Chapter 6 EASURE V W FURTHER dc ANALYSIS 15 REQUIRED ARIA RES CLOS TO THEIR FIX U SHORT CIRCUTS AND INTERRUPTIONS IN THE LAYOUT AWD ok REPLACE Ry MEASUCE WITACE DOS ACROSS Boum NO 14 APPLY THE VOLTAGE gt DIVIDER TROUBLESHOOTING PROCEDURE TO FIX UP SHORT CIRC TS AND INTERRUPTIONS IN THE LAYOUT AND OR NOMINAL DETERMINED BY VOLTAGE DIVIDER
262. thyristors or triacs When there are nearby radio or TV receivers check whether the instrument is properly grounded Try different points and check connections and coaxial cables Electrical discharge surface of components due to high humidity Loose cable contacts Cable movement caused noise microphon ics in PM tube THE SPREAD IN THE NUMBER OF COUNTS IS LARGER THAN MAY BE EXPECTED ACCORDING TO STATISTICAL FLUCTUATIONS WHEN MEASUREMENTS OF THE SAME SOURCE IN FIXED GEOMETRICAL POSITIONS ARE DONE EACH DAY Possible causes may be An irreproducible source positioning The use of different source holders or test tubes Changes in the absorbing medium dust or dirt in factories The timer uses the fluctuating AC frequency as time base The setting of the HV is irreproducible or the HV is unstable Irreproducible settings of the amplifier and or SCA Large temperature changes or too short warming up times of instrument Spurious counts Large AC fluctuations Unstable LV power supplies Bad earthing 75 Chapter 8 4 10 76 LOSS OF SPECTRUM RESOLUTION Possible origins are Disturbances in the HV supply ripple and fluctuations Detector colouration or a broken crystal A bad optical joint Unstable LV power supplies An unstable preamplifier or main amplifier Light leaks into the PMT or detector The deterioration of the photo cathode of the PMT An oscillating preamplifier Bad earth c
263. tiometer compensates the input voltage and the motor rotates until the error signal is minimized The most critical part is the potentiometer They wear out after 10 million turns so their expected life is 3 4 years in a nuclear medicine unit with 5 000 imagings per year 272 33 Chapter 11 COUNTING RATEMETER OUTPUT COLOR ADJUSTMENT DC SERVOMOTOR REFERENCE VOLTAGE I screw 7 coLoR RIBBON POSITION TRANSDUCER COLOR RIBBON CARRYING CAGE NUT ON SCREW SCREW COLOR RIBBON POSITION TRANSDUCER YELLOW SPRING TAPPER COIL EM COLOR RIBBON TAPPER SLUG CIN OOS N x POSES e NS X A S OKO 5 AN SCINTIGRAM PAPER PRINTING EDGE 11 17 Circuit diagram and mechanical construction of Fig a typical converter 273 Chapter 11 34 Wear could be one reason for the component deterioration but under used potentiometers can develop noises under tropical conditions as well However they are reduced to a normal level after a few hours of operation 11 2 4 7 Control logic The movement of the detector is under the control of the scanners logic system Its main functions are the sensing of the position of the scanning area determining boarder limit switches the position of the border limit proximity switches and the safety limit switches and to control the stepping motors
264. tion of the 24V and 24V supply line Most of the faults in the earlier version of this HV supply were the consequence of burning out of the polarity indication lamps Nowadays these lamps are replaced by LEDs Also there were sometimes problems with the tantalum capacitors due to the spikes which occur from switching an inductor on and off 5 6 2 Example 2 Canberra Model 3102 Another type of HV bias supply is the rather complicated one from Canberra Model 3102 This circuit has a feedback circuitry to stabilize the HV bias voltage Canberra even uses special ICs which are not very common on the market Fig 5 7 shows the circuit of the above mentioned bias supply It is controlled and regulated by a feedback loop and the ratings are up to 2mA at 2000V 96 19 Chapter 5 NOTE This is an example of a case when you cannot trust the circuit diagram There are some changes 1 the circuit which are not shown in the circuit diagram e g oscillator swing is from 10V to OV and due to the slow rate of the used operational amplifier it has a trapezoidal waveform The feedback resistor network R107 R111 is connected to 12V and not to ground The positive supply of the operational amplifier is connected to ground and not as it is shown the circuit diagram to 12V Therefore the oscillator operates without the module being switched on Also the component number IC104 does not correspond to the actual lay out which is
265. tions can be taken to avoid these effects place the dewar of the detector on a soft rubbery mat put sound absorbing material around the detector cap put some fine sand in the bottom of the dewar to a level that the end of the dipstick will be inserted in the sand this prevents bubbles from forming the surface of the dipstick end With the Si Li detectors the berillium window is the most sensitive part It can be easily broken high humidity will cause 287 Chapter 12 10 corrosion resulting in the appearance of microscopic vacuum leaks When not in use the detector should be protected with the plastic cap If stored for a longer period the detector top should be covered with a plastic sheet with some silica gel to avoid high humidity 12 1 6 Troubleshooting of Ge and Si Li Detectors The semiconductor high resolution detectors are normally bought together with the preamplifier The properties of the detector and with them its price are defined for the combination detector tpreamplifier dipstick With some detectors the preamplifier can be ordered separately as replacement to be installed locally There are several possible combinations configurations and each should be treated in a separate way i The ORTEC detectors are recognized by their shape the preamplifier is integrated in tthe cylinder of the detector head see Fig 12 7 This streamlined solution is practical for some measure
266. to perform step by step testing It makes everything more transparent 237 Chapter 11 DEDICATED INSTRUMENTS Chapter 11 11 DEDICATED INSTRUMENTS Previous chapters are devoted to the instruments that are used in nuclear research laboratories NIM modules and MCA Two examples of the instruments used in other applications are described below 11 1 SURVEY METER 11 1 1 Fields of Application Ionizing radiation dose rate meters or simply survey meters are the most important measuring instruments in radiation safety We have no sensory organ to guide us on the intensity of ionizing radiations present in our environment due to natural or artificial sources Without proper measuring systems one might be exposed to health deteriorating radiation levels Survey meters are used in radioactive ore prospecting as well If the instrument is not functioning according to specification the ore may not be located and the natural resource would remain hidden It is important to realize that if the survey meter is not functioning properly we might be harmed by radiation or loose ore fields The problem is that sometimes the fault develops very slowly without dramatic signs The repair staff and the user should know how to check the performance of the survey meter to overcome the hazards to health and property 11 1 2 Controls Turning On and Quick Functional Checks On most survey meters a single mult function rotary switch i
267. truments are needed Moreover instruments with both voltage and current trouble shooting capability help isolate electrical faults where the precise physical location is hard to identify shows a series of node and gate faults combination of tools used to troubleshoot the circuit As with all sophis ticated measuring instruments operator skill and circuit knowledge are key factors once the various clues or bits of information are obtained using the IC Troubleshooters The table typical and the BC F 35 Chapter 3 3 3 17 Break Out Box A tester for V24 RS 232 interfaces See sess oe The instrument is inserted into the RS 232 link LEDs show the status of each line With DIP switches each line can be interrupted and arranged also a low or high level can be applied A delay of two adjustable times is possible for each signal Such economic instruments are recommended for fast troubleshooting of serial interfaces ABC 55 Chapter 3 3 3 20 Prom Programmer 2365 suitable for programming Proms of the type 2716 to 27512 serial and parallel inter faces 512 k bit RAM internal memory The capabilities of such an instrument are programming 4 programming algorithms ing e g editing the buffer RAM CPU communication operation from a host computer emulation transfer data from buffer RAM to optional emulator edit interface to an external module
268. try with your own reference source and to use this data in future quick functional tests If you can cover more intensity ranges the better Your work investment will pay off in reduced troubleshooting time 11 1 3 Operating Principles of Systems with Various Detectors All survey meters have ionizing radiation detector and circuits to convert the detector signal carried information into dose rate information anda display unit The survey meters battery operated portable units With a few exceptions they contain DC DC converters for the detector supply as well as for the low voltage SIGNAL DETECTOR PROCESSING DISPLAY LOW VOLTAGE BATTERY HIGH VOLTAGE REGULATED Fig 11 3 Block diagram of a survey meter REGULATED SUPPLY SUPPLY 11 1 3 1 Dose rate meter with ionization chamber detector Fig 11 4 In this system a DC DC converter supplies a few hundred volts for the ionization chamber In most cases the low voltage electrode of the chamber is connected to a differential amplifier with FET inputs The phase inverted output of this amplifier is fed back to the common point of the chamber and the input of the amplifier through a very high ohm value specially designed and manufactured resistor Such a circuit configuration can convert very little current into voltage The differential amplifier improves the temperature stability characteristics of the system By changing the value of the fee
269. uence by hardware We have only to send output strobes and a Signal for direction pulses for the coils of the motor are generated by the hardware The hardware implementation has the advantage of relieving the CPU from dedicated timing loops also it is safe even if the CPU crashes The CPU only has to know when to send the next pulse This is mostly done on an interrupt driven basis The second method to drive stepper motors is completely handled from the CPU by 1 0 Ports PIA and current drivers The CPU has to provide via software the correct phases for appropriate lengths of time A typical example for the second method using an OPEN LOOP system is shown in Fig 10 12 Troubleshooting in such a system is very simple You can only check if power is applied to the drivers and if pulses are coming out of the PIA and passed through the drivers If there are no output pulses provided by the PIA refer to Section 10 6 235 Chapter 10 26 CPU output ports Stepper motor i 1 1 a Open coliector driver array Current Common limited 24V supply Fig 10 12 Open loop transistor driving circuit for 4 phase stepper motor In the other case a CLOSED LOOP system things become more complicated simple CLOSED LOOP system is represented in Fig 10 13 CONTROL Bus nput to Stepper Motor Coils Stepper Motor Position Encodes OH put from DATA Bus Position Encoder
270. ults for the left and for the right motion An additional comparator A86 LM 311 senses the polarity of the generated voltage and selects the counting direction up or down FRONT PANEL MOTOR ANALOG PROC 85 8 BIT COUNTER A82 A83 DIRECTION STROBE CLEAR LATCH 10 07 Fig 9 24 Cursor controller block diagram Some Troubleshooting hints follow 1 Check the voltage magnitude and the polarity at pin 3 A86 to the ground 194 23 Chapter 9 2 Is there a change in the polarity of the 86 output signal at pin 7 when rotating left and right 3 Can you observe the rectangular signal at pin 3 84 4 Are there strobe pulses of negative polarity at pin 1 A81 and pin 11 A82 and pin ll A83 5 Are counters A82 and A83 connected serially into 8 bit binary counter active Can you observe the rectangular signal at pin 9 and at the higher bits when you rotate the motor rapidly 9 11 DISPLAY BOARD WHAT IT DOES The task of the display board is to control the monitor and provide the information to be displayed on its screen Using the built in clock two digital signals LSYNC and FSYNC are derived to synchronize the monitor The display board also looks into the RAM using the direct memory access DMA to get the number of the stored counts in different channels These data are combined with the information about the MCA working conditions which have to be displayed in text form in tne lowe
271. unning permanently Its operation can be observed by connecting the oscilloscope to TP6 and using the corresponding ground TP7 to get a representative picture without superimposed oscillations In the pulse analyze mode clock pulses are passing NOR gates in 89 They can be observed at pin 6 and pin 11 of the before mentioned circuit When all the counting conditions have been met the synchronizing unit is activated The SYNC signal is delivered at pin 7 A83 Counting starts The address counter consists of A79 through A82 and is configured as a 14 bit ripple counter The 14th bit is used for under and overflow detection During ramp down sequence the ramp counter and ramp current are enabled and synchronized to the 100 MHz clock The resultant digital address in the address counter represents the magnitude of the ADC analog input The counting can be followed from stage to stage if the input signal jis high enough to activate the higher bits too and if the selected number of channels is sufficient For instance if the channel number was set to 512 then only the lower 9 bits will be active Set the oscilloscope time base to smaller time division values to display only a few periods of the observed signal Then move the probe to pin 5 A82 and set time division value to 1 or 2 microseconds per division Now you can observe the full length of the pulse train which should follow the height of the input pulse 184 13 Chapter 9
272. urrent low duty cycle pulse testing technique to test semiconductors even with resistive and capacitive shunt impedances Fast GU NO GO in circuit transistor testing Fast and thorough GOOD BAD out of circuit testing Tests FETs and SCRs in circuit or out of circuit Any test clip to any component lead gives positive emitter base collector identification on LO drive positive base identifica tion in HI drive Light Emitting Diodes indicate NPN OK or PNP OK Power requirements 6VDC from four AA cells Standby current 4mA average testing current l2mA 49 Chapter 3 30 3 3 6 Oscilloscope DC 100 MHz Dual trace signal delay delayed trigger 5mV lmV div 3 5ns n economic instrument for advanced troubleshooting and development work sorte oF a Specifications abbreviated VERTICAL AXIS Ch 1 Ch 2 identical 5V div Xl mode 1V div X5 mode 5mV div to lmV div to accuracy 2 attenuator 5mV div to input 1M 22pF f response DC DC to 100MHz 3 dB 5Hz to LOOMHz 3 dB operating modes Chl Ch2 QUAD ALT sensitivity 5V div DUAL ADD CHOP VERTICAL AXIS Ch3 Ch sensitivity O 1V div 1V div 2 attenuator 1 1 1 10 input coupling mode DC only TRIGGERING A modes Source AUTO NORM SINGLE FIX V MODE CH2 EXT CH3 1 1 and 1 10 LINE AC LFREJ HFREJ DC coupling VIDEO INTENSITY MODULATION INPUT
273. ust moisture condensation excessive line voltage fluctuations and transients instruments should be covered after use rarely used instruments should be turned on periodically and mechanically operated to prevent rusting and to dry out lubrication and safety check ups should be according to the manual only trained operators should use the instrument a log book should be kept on use and repairs reference tests and their results should be attached to the book 275 Chapter 12 RADIATION DETECTORS ajs Chapter 12 12 RADIATION DETECTORS This chapter presents a description of difficulties with the detectors most frequently used in advanced nuclear spectrometry Although a detector is directly and sometimes inseparably connected to electronics discussions on the behaviour and faults of electronic parts is avoided for this the reader should refer to Chapters 5 and 11 Furthermore attention is devoted entirely to the high resolution detectors simple detectors such as Geiger Mueller scintillation are described in Chapter 11 Accordingly the chapter starts with the high resolution x ray and gamma ray detectors 12 1 HIGH RESOLUTION X RAY AND GAMMA DETECTORS Today we find on the market the following types of high resolution detectors Coaxial pure germanium detector p type for gamma Planar pure germanium detector x rays Coaxial pure germanium detector n type x rays and gamma Si Li detector x ra
274. ut and if the corresponding binary number appears at digital adders 74L 283 A63 pins least significant b t 1 13 10 A65 pins 4 1 13 10 183 Chapter 9 12 A64 pins 4 1 13 10 and A63 pins 1 and 4 most significant bit we can assume that the ADC is working properly In order to observe the binary output the ADC board should be extracted and extended by using the extension card In the case of failure the signal processing should be followed step by step 1 Connect the oscilloscope probe to 5 and clip the oscilloscope ground to TP9 to observe the input signal Then repeat the observation moving the probe to the TP5 Note that the signal at TP5 follows the ascending side of the input pulse and remains constant after the peak has been reached This is the indication that the stretcher works properly If not skip the next steps and go to 2 One or two microseconds later the discharge process starts The slope of the linear approach to zero depends the conversion gain A few hundred millivolts below zero conversion is stopped and the ramp returns to zero The analog part of the conversion was successful Note the case when the input signal exceeds the upper level discriminator A28 setting The control logic then sets DUMP to logic 1 Q24 and Q25 are both conducting and fast discharge follows During the interval of the linear descent the zero pulses from the 100 MHz clock are counted The clock is r
275. ut out a STATUS byte In our case the Counter is the requester and would output the Status 42H and remove its service request If it would not have been the requesting device it would output a Status 00 The controller completes the serial poll mode by doing a Serial Poll Disable SPD If the Counter is the only possible source of the Service Request the controller can respond immediately by reading the data from the module which also clears its Service Request To read data from the Counter the controller responds to the Service Request through the Ready For Data RFD line via the Acceptor Handshake Read Clock Enable RCE is active once MY TALK ADDRESS and Read Clock RCL is sent to the counter to clock the bytes from the counters during S3 output sequencer After each LSB Least Significant Byte the output sequencer activates S4 to gate the message unit delimiter to the bus separates counter outputs After 54 of last counter 55 became active and gates ASCII Line Feed and EOI to the bus End Message Afterwards LB Last Byte is active and terminates the TALK MODE Following you will find a Block Diagram Fig 10 8 a Circuit Diagram Fig 10 9 and a description of the signals Table 10 3 Troubleshooting in such a system is limited because of its complexity First in many interfaces you will find large scale integrated circuits which support you with all signals used for the GPIB Most of them are set up and programmed via s
276. ve components check the power supply again Increase the output voltage of the variac to the nominal mains voltage but also measure the ac current used by the power supply This current should not be more than 20 of the fuse current since there is no load Readjust all supply voltages according to the circuit diagram service manual After this procedure the output voltage of the 5V line follows when the output voltage of the 24V line is increased Simultaneously measure both output voltages When the 5V line reaches around 5 6V the overvoltage protection should be activated In this case decrease the output voltage of the 24V line to the nominal value switch off the instrument to reset the memorized overvoltage and switch the instrument on again Then measure the output voltages to be sure that everything is properly set If the overvoltage protection did not trigger try to detect the defective components D13 Q20 Q190 or the passive components around them The components IC A5 015 and Q16 are there for power reset which is necessary for the microprocessor reset IC generates a fixed clock frequency The current limitation can now be checked For this purpose an ammeter series with a variable power resistor has to be connected to the output and simultaneously the output voltage has to be measured Increase the current by changing the resistor When exceeding 100 of the nominal current the output voltage sh
277. ve the outputs of A8 the outputs of A6 should be in the same state as the and 2 output lines of 8 Observe the scanning reset of channel A SCNRA signal at pin 13 of A38 check that it is synchronous with the strobe 1 signal pin 3 of A8 if at least one of the decades D7 and D6 has non zero contents and that it is synchronous with pin 2 of A8 otherwise If this is not the case multiplexer A38 must be checked after verifying that it receives the correct signal from flip flop A29 through gate A36a 8 4 2 Channel Data Multiplexer Latches Decades The BCD coded data from the decades of channels A and B is multiplexed by A37 to a bus connected to all the latch decoder circuits These are to be checked including the operation with the phase signal pin 6 of the latch decoders generated through 162 9 Chapter 8 23 The phase signal should be out of phase with the back plane signal pin 3 of A18 whenever a segment is to be ON and in phase if it is to be off If a segment is not ON while it is seen out of phase with the back plane signal it is possible that there is a misconnection or a ground path to inhibit the display of the segment most often this occurs at the conducting rubber contact with the crystal Otherwise the display is defective 8 5 TROUBLESHOOTING EXAMPLE DIGITAL LINEAR RATEMETER CANBERRA MODEL 2081 In this instrument the input signals are initially divided by 2 flip flop and further divid
278. wargrspp JOINS 342U2vw 44 7009 SWIM Auto TIME DODI SILENT F FOL 0207 IN 990 9732 TINGS IWON H WT v Fw CECI OSS TRON ST Imo T BLS MOS sem rw paw CIALIS T 9 2109 SE Do t Spectroscopy amplifier circuit diagram Fig 6 23b 139 36 Chapter 6 24 7 una Vos T tomay one wl 18 ob we 993 CN H NV vow 00 rtu E lt a 50 42 5 o n o rd ed ord p E c gt m 9 e ua 140 237 2 Chapter 6 3 Do not connect BNC cable to the front panel connector because sometimes the outputs are not properly terminated and therefore oscillation might occur 4 Place the input selector switch in the positive position Feed a positive signal from a pulse generator through the input plug to the amplifier pulse repetition lkHz pulse width about 100 msec to achieve a stable picture on the scope trigger your scope by the external trigger from the pulse generator Follow this signal with an oscilloscope probe 10 1 stage by stage and compare the pictures between circuit diagram and oscilloscope If at the output of a stage there is a discrepancy there is usually a fault in this stage Start measuring with the digital voltmeter the DC levels of the base emitter and collector of the various transistors A defective component can be detected by these measurements
279. with The problem is to order the best for a certain purpose To order the instruments at the lowest possible cost is not necessarily the best solution Some additional factors have to be considered 1 For which purpose the instruments are needed i e which field of troubleshooting development should be covered 2 Will the instrument be upgraded for additional purposes in the future 3a Is the manufacturer represented on the local market 4 1s the instrument supplied with all technical information and service manuals 5 How is the situation in servicing the instrument local service station shipment custom difficulties etc 6 Can the instrument be ordered together with spare parts accessories options service kits etc 7 Who is the user of the instrument level of experience and knowledge 8 Where will the instrument be used environmental situation These eight points may be extended according to special situations The instruments listed in the following pages are used in different nuclear electronics laboratories that have received assistance from the IAEA Considerable experience of experts is incorporated into this selection Nevertheless only point l and 2 mentioned above will be covered For a final ordering decision all other points should be considered The following listed instruments are to be understood as examples only This list also should be upgraded periodically old fashioned equipmen
280. wn excessively the signal Your feedback loop is over compensated pulse generator anda dual channel oscilloscope with at least 100 MHz bandwidth It must be equipped with two 1x probes and two 10x probes Do not use the 1x probes if this is not necessary to achieve a high sensitivity of your scope For an easier observation on the scope use an external trigger by sending to the oscilloscope input the advanced trigger signal from the generator Set on the generator 200ns delay Make sure that no false contacts exist in the cables connectors and probes Check the ground wires of the probes make sure that they are safely soldered to their alligator clips Add in series with each probe a 300 resistor to avoid spurious effects due to probe capacitance Having done this send the signal from the generator output to the input of the instrument under test Use the two channels of the scope to monitor for each part elementary circuit in your instrument input and output signals Ground the probes to the ground conductors that closest to the points you are going to monitor now Some ideas about how to proceed with the signal analysis will be discussed They will refer to particularly simple situations where the instrument is made only of amplifying parts all working in the linear range and not requiring any logic command More complicated situations will be considered afterwards with specific cases The analysis referred to i
281. y Odd Even None character length 5 6 7 8 bits of stop bits 1 1 5 2 Mode Simplex Half Full duplex Echoplex Yes No Line feeds 0 1 2 CR implies LF LF implies CR Transmission mode Asynchronous Synchronous Polarity Positive Negative In summary all items should be checked for proper optioning to permit successful installation Both devices have to be SETUP to match each other For example if device is set to 4800 bps the other one has to be set to the same baudrate The same has to be done with all other items listed above In most cases these changes can be done either by DIP switches located on the interface board or by software in a PC Let us have a closer look at the basic hardware of such an interface Normally you have data on a parallel data bus in most cases 8 bits wide This data has now to be converted into a serial one which is done in a so called USART Universal Synchronous Asynchronous Receiver Transmitter This circuit also takes care about the hardware handshaking lines as shown in Fig 10 2 RS232 25 pln connector pin for modem computer CONTROL Bus u R G CTS T 8 2 3 Tib DATA BUS I t C C OTR Fig 10 2 Parallel to serial conversion with a USART 217 Chapter 10 8 Computer RS 232 interface supports via USART Fig 10 2 DSR RTS and CTS control lines The 25 pin connector pins are labeled from the terminal s point of view while the inver
282. ys Pure Si Li detector x rays Surface barrier detector alpha and beta The Ge Li detector which started the revolution in the field of high resolution spectroscopy is not produced anymore by the respected manufacturer of semiconductor detectors 12 1 1 Selection of a High Resolution Detector When ordering a germanium detector for gamma rays one must specify l Resolution an average detector will have resolution 1 8 keV 2 Efficiency varies from 8 to 402 3 Type of cryostat i e the size of the dewar and the position of the dipstick NOTE The pr ce of a Ge detector steeply increases with the size efficiency and with improved resolution NOTE A detector with a vertical dipstick is the most common type Other shapes of the dipstick are for special applications 279 Chapter 12 2 For pure planar germanium detector we must define 1 Thickness of the detector 2 Area of the detector in square mm 3 Resolution in keV 4 Size of the dewar and type of the dipstick Planar detectors are used in measurement of x rays with energy above 20 keV Due to intense escape j peaks they cause difficulties in interpretation of complex spectra When buying Si Li detector we must determine 1 Resolution of the detector in keV an average detector has 180 eV 2 Area in square mm the usual sizes are 30 and 80 sqmm 3 Type of cryostat and dipstick 4

Download Pdf Manuals

Related Search

Related Contents

eSense Skin Response User Manual  Betriebsanleitung zum Bordmonitor mit Navigation und  Valueline VLVP31045B10  Manuel d`utilisateur  Keynotes  Ground Penetrating Radar GPR - RJM Utility Á Drain Cleaning  McCulloch MCB2203 Blower User Manual  Guida dell`utente di Synology DiskStation Basata su DSM 4.1  View owners manual  

Copyright © All rights reserved. Failed to retrieve file