.. THE HYBRIDER .. SERVICE MANUAL
Contents
1. TUBE TEST SET UP SHORTS TEST EMISSION TEST GRID LEAKAGE TEST LIFE TEST FILAMENT VOLTAGE SENSITIVITY Sse oie cece Meares SET UP FOR NEW TUBES A PIN ELIMINATION B FILAMENT LOAD D SET UP SOCKET SET UP EXAMPLE OF SETTING UP THE TC28 FOR NEW TUBES TRANSISTOR TEST GAIN TEST LEAKAGE TEST DETERMINING BASING LOCATING LEAKAGE CHECKING DIODES CIRCUIT DESCRIPTION Lesern a aede dust ras euis THEORY 05 EMISSION TEST tector rtu ab d GRID LEAKAGE TEST ae D a ee ets THEORY OF OPERATION TRANSISTOR TEST GAIN TES mise pert POWER SUPPO Y abate 2KHz OSCILLATOR AND SIGNAL AMPLIFIERS LOGIC CIRCUIT AND INDICATOR DRIVE ii ette LEAKAGE TEST SERVICING THE TC28 DISSASSEMBLY INSTRUCTIONS CTS Rem LOIN ot TROUBLE CHARTS SERVICE AND WARRANTY MO 00 41 41 4 AADA INTRODUCTION D2. SCHEMATIC DIAGRAM THE TC28 HYBRIDER FOIL SIDE COMPONENT SIDE
3. SIOUX FALLS SOUTH DAKOTA 57107 Toes TUBE amp TRANSISTOR TESTER SCHEMATIC AND PARTS LIST SE NIC ORE THE ALL AMERICAN LINE OF HIGH QUALITY TEST EQUIPMENT TC28 PARTS LIST SCHEMATIC PART DESCRIPTION PRICE REFERENCE NUMBER BOARD MOUNTED COMPONENTS IC101 69G9 IC Quad Op Amp LM3900 2 50 IC102 69G10 IC Quad Nand Gate SN7400 1 25 101 102 19A28 Transistor NPN 2N5172 50 TR103 19C11 1 FET N channel 2N5457 1 75 104 19 16 1 Transistor PNP 2N5227 75 101 104 105 111 114 5005 2 Diode 1N4148 25 CR102 103 50 3 1 Diode IN34A 25 106 50 4 2 Diode Zener 8 2V 75 CR107 109 16510 Rectifier 0 5 400 PIV 50 CR108 110 50C4 13 Diode Zener 5 1V 1 00 R101 15 7 2 Control 10K Leakage Cal 75 R103 15C7 8 Control 1 2M Emission Cal NS R105 15C7 6 Control 500K Shorts Cal 75 R132 15 7 2 Control 10K Grid Leak Cal MS R138 139 14 49 9 Resistor 150 Ohm 5W 10 25 C101 104 110 112 115 246126 Capacitor 0 01 mF 50 C106 108 111 24G293 Capacitor 0 lmF Mylar 50 C109 24G289 Capacitor 0 47 mF Mylar 9 113 114 246118 Capacitor 100 Lytic 50 C116 117 24G181 Capacitor 200mF Lytic 1 00 CHASSIS MOUNTED COMPONENTS R10 15C1 38 Control 200 Ohm Meter Zero 1 25 R2 3 14B49 9 Resistor 150 Ohm SW 10 25 Cl 24G120 Capacitor 1OmF Lytic 25 2 246140 Capacitor 002mF 25 C3 24G25 Capacitor 220pF Disc 25 28B58D Transformer Power amp Filament 15 25 SWI 25G197 Switch Slide L
4. 0618 TWX 910 695 3226 Western Sales amp Service Central West Sales amp Service 833 Mahler Rd 3200 Sencore Drive Burlingame CA 94010 Sioux Falls SD 57107 A C 415 697 5854 A C 605 339 0100 TWX 910 375 3307 TWX 910 660 0300 Southeastern Sales amp Service Northeastern Sales Office 2459 Roosevelt Hwy Suite B9 1593 H Central Avenue College Park GA 30337 Albany NY 12205 A C 404 768 0606 A C 518 869 0996 TWX 810 751 3546 TWX 710 444 4969 32 Page 32 Sencore Regional Offices The Northeastern Sales Office address has been changed to 1237 Central Avenue Albany New York 12205 518 459 6040 The Southeastern Sales Office address has been changed to 2459 Roosevelt Hwy Suite B3 College Park Georgia 30337 404 768 0606 ADDITIONAL APPLICATION NOTES IN CIRCUIT TESTING There are some rare cases where a good transistor may test BAD by the Hybrider when testing in circuit This will occur for a circuit where the base to collector resistance is less than 100 ohms or when large electrolytic capacitors of 50mF or more are connected directly between the base or collector leads of the transistor and ground Therefore it is recommended that if the in circuit test of a transistor indicates BAD it should be removed and retested for gain before a replacement is installed This retest should also include the out of circuit leakage test If a transistor tests BAD in circuit and GOOD out of circuit this may indicate other p
5. Current LOAD switch Cathode Current A 50mA plus 2 7mA B 20 50mA G 7 C 15 30mA H 5 8mA D 10 16mA J 5mA or less E 6 12mA The current that the C LOAD switch 15 set to 1s the normal cathode current under normal bias conditions as listed in the tube manual If a tube manual 15 not handy compute the cathode current by the voltage drop across the cathode or plate load resistor in the circuit or from the schematic by using Ohm s Law D SET UP The D switch 1s used to pick up the control grid for the test on the tube It was discovered many years ago that approximately 97 of the electrons would go to the control grid when checking cathode emission This 1s now used as the pick up element In the example of Figure 2 the D switch would be set to one of the control grids that 1s not 1solated If pin 6 were to be isolated the D switch would be set to pick up pin 2 The only exception to the above is socket number 10 where 11 on the tube base is picked up with the first position of the D switch Sockets number 3 and 8 are wired identically except that socket number 8 has three pins not connected This socket is used to isolate extra connections where more than two base pins are connected to the same element such as in the 1X2 high voltage rectifier The seven pin sockets 4 and 7 are alike except that the filament pins on socket 4 are 3 and 4 while on socket 7 they are 1 and 7 SOCKET SET UP The
6. and 6 and the screen grid on pins 1 and 7 with pin 9 possibly connected to some pin internally With the A PIN ELIMINATION switch we will isolate the extra pins For our example we will push switches 6 and 7 down to the isolation position along with switch 9 to eliminate any possibility of this pin caus ing a false indication THIRD Determine the filament voltage In this case it is the 6JE6 so that the filament switch B will be set to 6 The first set of numbers on the tube generally indicate the filament voltage of the tube On foreign tubes consult a substitution guide to find the filament voltage and characteristics that can be used to check the tube FOURTH Select the current range that the tube is to be checked at using the information under C LOAD switch section of SETUP FOR NEW TUBES For our example the A position would be used as the 6JE6 draws a very heavy plate current under normal use Then perform the tests as previously described 2 TRANSISTOR TESTS GAIN TEST The gain test on a transistor or FET with the TC28 is actually simpler than testing atube There is no need to know the transistor basing polarity or even if it is a transistor or an FET Merely connect the leads in any combination and press the test buttons Follow the procedure below to make a gain test on a transistor or FET 1 Remove power from the equipment containing the device to be tested and discharge all power supply filter capacitor
7. before the test is made All the numbers correspond to the tube base pin number except for socket number 10 the compactron where pin 11 is connected to PIN ELIMINATION switch number 1 If no isolation is needed all switches should be in the uppermost position After each tube is tested push the RESET switch to the right to place all switches in the up position Each can be moved independently of each other either up or down or set with RESET switch BASING UE TERMINAL CONNECTIONS Pin 1 Grid 2 Pin 7 Grid 2 Pin 2 Grid 1 Pin 8 Grid 3 Pin 3 Cothode Pin 9 Internol connection Pin 4 Heoter do not use Pin 5 Heoter Cop Plote Pin 6 Grid 1 BOTTOM VIEW Fig 2 9QL Basing for 6JE6 Tube B FILAMENT This switch selects the filament voltage applied to the tube under test from 1 volt to over 50 volts The twelve position switch selects a voltage range and with the unique design of the filament transformer 9 the tube under test will load the transformer to obtain the correct volt age for testing When setting up a new tube simply set the B FILAMENT switch to the correct voltage or voltage range LOAD This switch selects the proper AC voltage to be applied to the plate of the tube as well as the correct load resistor so that the tube s designed current can be set and the tube checked under full load The current ranges for the settings of the C LOAD switch are as follows LOAD switch Cathode
8. of R111 and R112 will be 180 degrees out of phase with the base signal The base signal from the 2KHz oscillator is amplified by IC1C and the Icollector signal is amplified by ICID The outputs of IC1C and coupled to the logic circuit of IC2 that provides an output to the meter and speaker only when the two input signals are 180 degrees out of phase This provides both audio and visual indication of a good transistor 21 POWER SUPPLY tL But CRIIO 4 14 pem 1 ICI 4 0j POWER em 27 Da T 82V CRIO8 T3 l4 VAC 5V FROM TRANSFORMER 5W Fig 9 Power Supply Schematic The 14VAC from the transformer is rectified by CR107 and CR109 shown in Figure 9 and filtered by C116 and C117 to produce 16 volts DC This voltage is regulated by R137 and CR106 to produce 8 2 volts DC for the bridge circuit Positive and negative 5 volts DC for transistor test volt ages are obtained from CR110 CR108 and R138 The plus 5 volt supply is filtered by C113 and the minus 5 volt supply is filtered by C114 2KHz OSCILLATOR AND SIGNAL AMPLIFIERS IC1B is connected as a square wave oscillator operating at approximately 2KHz as shown in figure 10 The frequency of operation is determined by R108 and C101 The amplitude of the output signal is set by the ratio of R106 and R107 TR101 and TR104 operate as dual emitter followers providing low impedance source for the 2K Hz signal TR
9. sockets on the TC28 have the filament pins prewired to eliminate the extra setup that is involved The actual pin connections can be seen on 10 the schematic diagram of the unit Note that the two octal sockets have different filament connections Socket number 1 1s for filaments on pins 2 and 7 while socket number 2 is for filaments on pins 7 and 8 Sockets 3 and 8 have filaments on pins 4 and 5 while socket number 13 is for special Hi Fi tubes with filaments on pins 1 and 2 There are two novar sockets that are wired identically Socket number 5 is for the standard novar based tubes while socket number 12 is for the magnoval based tubes The pins on the magnoval based tubes are larger in diameter than the standard novar base and can damage the novar socket All magnoval tubes are checked in socket number 12 to prevent damage to the regular novar socket number 5 When selecting the socket for new tube select the socket for the filament wiring as well as the socket the tube should fit into EXAMPLE OF SETTING UP THE TC28 FOR NEW TUBES Let s use for our example the 6JE6 shown in Figure 2 This tube is a standard novar based tube with the control grid tied to two pins on the tube base FIRST Determine the socket to use In this case the tube is a standard novar base tube so that socket number 5 will be used SECOND All the pins that must be isolated for testing must be noted In this example we have the control grid on pins 2
10. 101 and TR104 are both biased off and have a common emitter load resistor R118 TR10I passes the positive portion of the square wave and TR104 passes the negative portion The total square wave signal then appears across R118 The 2K Hz signal is coupled by R119 SW4H and the test switches to the base of the transistor under test It is also coupled to the non inverting input of IC1C by C104 and R120 22 RII RII2 OF TRANSISTOR Fig 10 2KHz Oscillator and Amplifiers Schematic ICIC amplifies the signal applied to the base of the transistor under test The amplified signal from the output of ICIC is coupled by R123 to input 2 of IC2 ICID amplifies the signal from the collector of the transistor under test The amplified signal from the output of ICID 15 coupled by 125 to input 4 of IC2 LOGIC CIRCUIT AND INDICATOR DRIVE The logic circuitry of IC2 is the heart of the TC28 It is here that the base and collector signals from the transistor under test are compared and the differentiation made between a good and a bad transistor IC2 15 actually quad two input NAND gate truth table for the NAND gate shows that the only time that the output of the gate is zero is when both inputs are positive The input and output signals in Figure 11 show operation of the circuit for a good transistor With a good transistor connected to the TC28 the base signal coupled into pin 2 of IC2A will be out of phase with the collector
11. ESCRIPTION Numerous solid state devices are finding increasing application in tele vision and other home entertainment equipment These devices are also being used in conjunction with a multitude of tube types to produce the hybrid sets To be effective in the field service of these units the service technician 1s faced with transporting a rather cumbersome and costly array of test equipment The Sencore engineering staff is aware of the problems and needs encountered in the service industry In response to these needs the ever popular Mighty Mite Tube tester has been expanded to incorporate the features of Sencore s latest solid state device tester the TOUCH TONE CRICKET Now in one compact rugged easy to use unit exists the ability to completely and reliably test the tubes transistors FET s and diode devices found in modern home entertainment equipment FEATURES A single instrument for fast accurate testing of tubes transistors and FET s without complicated set ups Pin elimination switches for greater capability in tube tests as new types are announced Full cathode current emission test of tubes Sensitive 100 megohm grid leakage test in addition to regular shorts test all on a large easy to read meter Complete test for transistors and FET s including in circuit gain and out of circuit gain and leakage with NO set up or basing data required Rugged construction throughout including protection against ove
12. ET To determine if the device is a transistor or FET and the basing diagram it is necessary to insert a 100K ohm variable resistor in series with the base gate lead Perform the Gain Test with the control at zero ohms and increase the resistance in 10 steps Retest both buttons at each step until the device tests good on only one button This indicates the device is a transistor If the device still tests good on two buttons with the total 100K resistance in series with the base gate lead it is an FET Since the source and drain are interchangeable on an FET it is not possible to determine the exact basing To determine the basing a transistor proceed as follows 1 With the transistor out of circuit connect the TC28 and determine which two test buttons produce a good indication 2 Refer to the table in Figure 3 to determine the base lead and connect 100 ohm control in series with it 3 Retest the transistor and note which test button produces a good indication Increase the resistance of the control as necessary until the transistor tests good on only one button Note the button that produces the good indication 4 Refer to the table in Figure 3 to determine the basing of the transistor TEST SWITCHES TEST SWITCHES IBCO full T full scale 5 ENET Fig Lead Basing p PEO prot Ze THE S ENCORE 3200 SENCORE DRIVE
13. IFE TEST 1 00 SW2 25A154 Switch Rotary FILAMENT 4 50 SW3 25A157 Switch Rotary LOAD 3 25 SW4 25A196 Switch Rotary FUNCTION 7 25 59 5 25A158 Switch Rotary SELECTOR 3 50 SW6 15 25A155 Switch Slide PIN ELIMINATION 2 75 85 16 25A156 Switch Slide RESET 75 SW17 18 19 20 21 22 25 186 Switch PUSH Push 3 50 MI 23C51 Meter 6 100uA 22 75 SCHEMATIC PART REFERENCE NUMBER DESCRIPTION PRICE 20612 Neon Bulb No 2 25 1 51 48A2 2 Speaker 2 8 ohm 2 75 ASSEMBLIES 108B107 Socket Panel Assembly 24 50 143A65 Printed Circuit Assembly 42 25 143A58 1 Push Switch Assembly 7 25 143A58 2 Push Switch Assembly 7 25 168612 Hook and Cable Assembly 10 00 110C311 Case Assembly 25 00 110C313 Cover Assembly 15 25 MISCELLANEOUS 26G4 Socket Octal 1 amp 2 50 26G65 Socket 10 Pin min 3 50 26G63 Socket 7 Pin min 4 25 26656 Socket Novar 5412 50 26G23 Socket Nuvistor 6 50 26G2 Socket 7 Pin min 7 25 26G3 Socket 9 Pin min 8 amp 13 25 26815 Socket Loctal 9 3 25 26G21 Socket Compactron 10 50 26G54 Socket 10 Pin min 11 50 26G183 Socket Transistor 1 25 266105 Clip Plate 75 21 32 Knob Bar Pointer 75 21 33 Knob Meter Zero 278 21A44B Glamour Cap Black 25 21A44R Glamour Cap Red 25 21A59R Glamour Cap Large Red 25 21A58 Pushbutton 25 278614 2 25 37 16 Rubber Foot Bottom 25 37 26 Rubber Foot Back 25 8 109 Escutcheon 3 25 Components not listed are stand
14. Make the gain test and note which two test buttons result in a good indication 2 Switch to the LEAK AGE test and press the two buttons that gave a good gain test This test checks the ICBO and ICEO leakage values of transistors and the IGDO and IGSO leakage of FET s These leakages should measure zero for FET s and small silicon transistors High power silicon and small germanium transistors may indicate up to 100uA leakage while germanium power transistors may indicate up to 3000uA and still be acceptable 3 Press the remaining four buttons Two of these will result in a full scale leakage reading and the other two may or may not indicate leakage depending on the transistor junction FET will indicate full scale on all four remaining buttons while a MOS FET should indicate leakage on only two buttons If desire to determine the exact type leakage for a particular transistor refer to the Locating Leakage section of this manual DETERMINING BASING If the device being tested checks good on two of the test buttons it is either a standard transistor or an FET To determine if the device is transistor or FET and the basing diagram if it is a transistor it is necessary to insert a resistor in series with the base gate lead The value 13 of this resistor will depend on the transistor being tested but the minimum value to use is 10K If the device still tests good on two buttons the value of the resistor will have to b
15. SW4E R8 TO SW5 amp CATHODE R9 OF TUBE SWAC TO SW5 amp GRID OF TUBE Fig 7 Emission Test Circuit The cathode emission test puts AC voltage between the control grid of the tube under test and the cathode with a load resistor 1n series with the cathode to develop a pulsating DC voltage The C LOAD switch selects the different size load resistors and applied voltage so that a full range of current is available from less than 5mA to 120 The tube under test rectifies the applied AC voltage and develops a voltage drop across the load resistors through R9 The pulsating DC voltage is coupled through the filter network of R103 and C110 to smooth it to a pure DC voltage This voltage is applied to the gate of TR103 through an additional isolation and filtering network of R127 R128 R131 and C112 shown in Figure 6 The resultant DC voltage is coupled through SW4D and upsets the balance of the circuit causing the meter to read up scale in proportion to the emission quality of the tube 19 GRID LEAKAGE TEST In the grid leakage test the control grid of the tube under test is made negative to all other elements in the tube by connecting the grid to ground through the 30 megohm gate resistor consisting of R127 and R128 of Figure 6 and applying 8 volts to all other tube elements If the tube has any grid leakage or contamination causing the grid to emit electrons the flow of electrons will be through the gate resistor Any
16. TC28 HYBRIDER SERVICE MANUAL S ENCORE Y e 7 4 the all american line SAFETY REMINDERS When testing electronic equipment there is always a danger present Unexpected high voltages can be present at unusual locations in defective equipment The technician should become familiar with the device that he is working on and observe the following precautions 1 When making test lead connections to high voltage points remove the power If this cannot be done be sure to avoid contact with other equipment or metal objects Place one hand in your pocket as a safety precaution and stand on an insulated floor to reduce the possibility of shock Discharge filter capacitors before connecting test leads to them Capacitors can store a charge that could be dangerous to the tech nician Be sure your equipment is in good order Broken or frayed test leads can be extremely dangerous and can expose the technician to dangerous potentials Remove the test leads immediately after the test has been completed to reduce the possibility of shock Do not work alone when working on hazardous circuits Always have another person close by in case of accident Remember even a minor shock can be the cause of a more serious accident such as falling against the equipment or coming in contact with high voltages TABLE OF CONTENTS SAFETY REMINDERS INTRODUCTION DESCRIPTION FEATURES SPECIFICATIONS CONTROLS GENERAL OPERATIONS
17. ard replacement parts and may be purchased locally When ordering parts please specify instrument model number schematic reference part number and description Please include remittance check or money order with your order otherwise invoices will be shipped C O D Minimum billing is 3 00 Prices and specifications in effect at date of printing and are subject to change without notice TUBE NOTES LALL CAPACITANCES GREATER THAN ONE ARE pf LESS THAN ONE ARE pf UNLESS OTHERWISE NOTED 2 DENOTES GROUND DENOTES CHASSIS X DASHED LINES REPRESENT MECHANICAL PARTS AND CONNECTIONS 4FUNCTION SWITCH SHOWN IN OFF POSITION S ALL FILAMENT CIRCUIT VOLTAGES MEASURED WITH RESPECT TO GREEN LEAD OF TI ALL OTHER VOLTAGES MEASURED WITH RESPECT TO CIRCUIT GROUND WITH 15 MEGOHM INPUT DIGITAL MULTIMETER amp FRONT PANEL CONTROL NAMES ARE ENCLOSED IN A BOX 7 BOARD CONNECTIONS CORRESPOND SCHEMATIC REFERENCE NUMBERS re DVANU 2KHz OSCILLATOR CRUZ CRUS Chia 5 BOARD 43 58 BOARD 43A65 D OMT ROA 6 8135 OMIT CIS CIO T Tros FUNCTION SWITCH BLOCK DIAGRAM
18. area 2 on the meter it will give trouble in the circuit and should be replaced REJUVENATION If you wish to rejuvenate a small tube merely increase the filament voltage by setting switch B one setting higher for ten to fifteen seconds This will super heat the cathode and boil out more emitting material from under the oxide coating This is only a temporary measure as rejuvenation of a receiving tube will not last very long SET UP FOR NEW TUBES New tubes can sometimes be a problem as they may not be listed in the set up chart This can be especially true on new receivers just introduced by the set manufacturers Though new tubes are seldom being added at the present time new tubes will undoubtedly appear in the future With an understanding of the setup controls and what each does you can set the Hybrider from a tube manual or even the schematic of the receiver itself A PIN ELIMINATION The A PIN ELIMINATION switch is used to isolate internal connections of two pins to the same element of the tube so that a test may be made For example the tube basing shown in Figure 2 is a 9QL basing The con trol grid is tied to pins 2 and 6 the screen grid to pins 1 and 7 and pin 9 is an internal connection that could be connected to any pin inside of the tube To eliminate any shorts indication other than that which are true shorts in the tube the PIN ELIMINATION switches 6 7 and 9 would be set in the down position to open these pins
19. as was caused in the emission check but will show up grid leakage If the grid leakage indication climbs into the BAD area on the meter reduce the filament voltage and see if the meter remains in the bad area If it does so then the tube will give trouble in the circuit and should be replaced If the meter drops off rapidly back into the GOOD area then the tube is good If the tube passes all of the above tests it can be considered good and need not be replaced If the tube is in the questionable area on any test it becomes a value judgement based upon circumstances as to whether or not it should be replaced LIFE TEST If the meter needle climbs very slowly into the GOOD area or Questionable area of the meter on the Emission test the life expectancy of the tube can be considered much less than if the meter indicated GOOD in a 7 shorter period of time Also if the needle should climb into the GOOD area and then fall off life expectancy can be considered much less A general measure of the usable life remaining in a tube can be obtained by using the Life test position of the TC28 Hybrider Simply slide the LIFE TEST switch to the right and hold it for a few moments Observe the emission level of the tube during this time If the emission remains the same or drops only slightly the tube can be considered good If the emission falls off quickly into the questionable or bad areas it may be wise to replace the tube The rapid dr
20. athode on the H K position of the D Switch This is a normal condition and these tubes are indicated in the setup book by an asterisk EMISSION TEST If the tube passes the SHORTS test rotate the Function switch to the EMISSION position and read the emission quality of the tube on the top scale of the meter A tube indicating in the questionable area has an emission level much lower than normal It s replacement would be determined by you and your customer based on the nature of the circuit in which the tube is to operate GRID LEAKAGE TEST If the tube reads in the GOOD area of the meter and passes the EMISSION test switch to GRID LEAKAGE and read the grid leakage of the tube on the GRID LEAKAGE scale of the meter This is a very important check and will pinpoint troublesome tubes that may otherwise check good If the meter is indicating in the GOOD area of the scale but slowly rising wait a minute or so to allow the meter to stabilize before judging test results On large power tubes such as a horizontal output tube do not make a grid leakage check after an extended emission check If the tube is left in the emission check position for several minutes the grid will heat up and when switched to grid leakage will read higher than normal Allow the tube to cool slightly before the grid leakage check You can expedite the grid leakage check by raising the filament voltage for a few seconds This is not the same overheating
21. base open Emitter positive with respect to collector for an NPN transistor IECO is a measurement of the transistors ability to block reverse voltages such as would be encountered in circuits with an inductive load in the collector In FET s this current would be called 1DSO and should dicate full scale because of the normal conduction of the low resistance drain source channel IEBO Button 4 IEBO is the leakage current that flows in transistors when a voltage 1s applied between emitter and base with the collector open and the emitter base junction reverse biased Emitter positive with respect to base for NPN transistor IEBO is most important in pulse circuits where the base 1s driven deep into reverse bias and the leakage current could influence the pulse shaping circuits In an FET this leakage 1s called IGSO and 15 a measurement of leakage current that flows from gate to source with the gate source junction reverse biased for junction FET s Even a small up scale deflection should be cause to reject a small silicon transistor or any FET Larger silicon and small germanium tran sistors may safely indicate up to 500 of leakage while some special high power germanium transistors may indicate up to 3 000uA and still be within manufacturers specifications ICEO Button 5 ICEO is the leakage current that flows in a transistor when a voltage 1s applied between the collector and the emitter with the base 16 open C
22. circuit whose base to collector resistance is less than 100 ohms or when large electrolytic capacitors of 50uf or more are connected directly between the base or collector leads of the transistor and ground These situations are not usually found in typical circuit applications Therefore it is recommended that if the in circuit test of a transistor indicates BAD it should be removed and retested for gain before a 12 replacement is installed This retest should also include the out of circuit leakage test If a transistor tests BAD m circuit GOOD out of circuit this may indicate other problems in the circuit First check the schematic for resistors of less than 100 ohms between base and collector or electrolytic capacitors of 50uf or more connected to the transistor base or collector If these are not found check the circuit board for the possibilities of 1 Shorted foils on the board 2 Large resistors connected to the transistor which may have changed value or become shorted LEAKAGE TEST It 1s possible for a transistor or FET to have good gain and still not work in the circuit because the leakage upsets the DC circuit values The leak age test on a transistor is nearly the same as the grid leakage test of a tube To make the leakage test proceed as follows 1 Remove the transistor from the circuit and plug it into the transistor socket on the test panel or connect the test leads to the leads of the device
23. current flow through the resistor will cause a voltage drop across the resistor resulting in an unbalance in the bridge circuit The meter will read upscale in proportion to the amount of grid current in the tube under test A leakage of 100 megohms or less will cause the meter to read into the BAD area A leakage of 100 to 200 megohms will cause a meter reading in the questionable area and a leakage of 200 megohms or more will read in the GOOD area on the meter A leakage of 100 megohms represents a grid current in the tube under test of 5 microamps SHORTS TEST CIOS RIO2 40Vrms 06 SW4E CRIO2 TO SW5 AND SW4C TUBE PINS TO GATE TRIO3 Fig 8 Shorts Test Circuit 20 The shorts test utilizes the Sencore stethoscopic approach where each every element in the tube is checked against all other elements A voltage divider consisting of C105 and R102 figure 8 is placed across the 40 volt secondary of the transformer The 40 volts AC RMS is divided down to approximately 34 volts RMS The lower voltage is necessary to prevent arc over and breakdown in nuvistors and frame grid tubes C106 isa coupling capacitor which prevents any DC action of the tube from up setting the shorts test Any shorting resistance present between the tube elements will upset the action of the voltage divider which will in turn increase the AC voltage at the input of the peak to peak detector comprised of CR102 and CR103 The ou
24. e both meter and speaker in dications inoperative CONCLUSION Check and replace as necessary wiring and test leads continued on next page 30 CONCLUSION Check for plus 4 volts at pin 11 of IC2 and 4 volt 2KHz pulses at pin 12 with button 1 push ed If both signals are present troubleshoot defective indicator circuit If one signal is missing replace IC2 NO CONCLUSION Start at base of TR101 locate where 2KHz signal is lost NO CONCLUSION Use scope to locate where 2KHz signal 15 lost NO CONCLUSION Trace signal back to out put pins 9 and 4 of IC1 If no output at pins 9 and 4 and power supply connections are good replace IC1 31 YES Remove transistor and connect scope ground lead to green test lead press button 1 and measure signal on yellow and red leads Does yellow lead measure 3 vp p and red lead measure 5 volts YES Connect known good transistor to the TC28 green lead to emitter yellow lead to base and red lead to collector Select the correct polarity press button 1 and using a dual trace scope check for out of phase signals on inputs 3 and 8 of IC1 Are proper signals present YES Check for out of phase signals at inputs 2 and 4 of IC2 Do signals swing from 5 volts to 4 volts DC YES CONCLUSION If power supply voltages are n
25. e increased in 10 steps 10K 12K 15K etc until it tests good on only one button If the device is still testing good on two buttons with a 100K resistor in series with the base it is an FET Since the source and drain are interchangeable on an FET it is not possible to determine the exact basing To determine the basing on a transistor proceed as follows 1 With the transistor out of circuit connect the TC28 and determine which two test buttons produce a good indication 2 Refer to the table in Figure 3 to determine the base lead and connect a 10K resistor in series with it 3 Retest the transistor and note which test button produces a good indication Increase the value of the base resistor as necessary until the transistor tests good on only one button Note the button that produces a good indication 4 Refer to the table in Figure 3 to determine the basing of the transistor TEST SWITCHES e TEST SWITCHES IBCO full scale full scale caor 1 2 3 4 5 6 5 5 p 5 5 Fig Lead Basing LOCATING LEAKAGE In some cases it may be desirable to determine the exact nature of leakage in a transistor With the test switches on the TC28 there is need to 14 connect to th
26. e transistor four different ways the test switches do it for you To locate the exact nature of the leakage proceed as follows 1 Determine the basing of the transistor or FET Connect the green test lead to the emitter the yellow test lead to the base and the red lead to the collector If the device is an FET connect the yellow test lead to the gate and the red lead to either the source or the drain Connect the green lead to the remaining element of the FET 2 Refer to Figure 4 and press the test button corresponding to the desired leakage test Note that for regular transistors buttons number 2 and 6 will produce a full scale leakage indication corresponding to the conduction of the forward biased base emitter and base collector junctions respectively junction FET s will produce a full scale reading on buttons 2 and 6 corresponding to the forward conduction of the gate diode and on buttons 3 and 5 corresponding to the current flow through the low resistance source drain channel MOS or IG FET s should only produce a full scale reading on buttons 3 and 5 corresponding to the current flow through the channel TEST SWITCHES c TEST pua LEAD COLOR GREEN E S o YELLOW se P RED IGDO E he Fig 4 Leakage Chart 3 following is an explanation of which leakage 1 is measured with each test button and its importance to the operation of the transistor or FET This information is sum
27. ed into the socket 1 on the TC28 socket panel Some of the calibration adjustments for the TC28 interact and for this reason the following adjustment procedure must be followed There are six calibration controls located on the printed circuit board in the TC28 Refer to Figure 14 for the location of these controls The first three adjustments have to do only with the tube test functions of the TC28 The remaining three adjustments pertain to the transistor test portion of the TC28 1 To begin the calibration procedure remove the TC28 from its cabinet and with the unit in its normal operating position adjust the mechanical zero adjust on the meter of the TC28 for a 0 indication 2 Apply 105 125 VAC power to the unit and turn the TUBES TRANSISTORS Function Switch to the NPN LEAKAGE position Connect the positive terminal of a DC milliameter to the red test lead Connect a 2000 ohm variable resistor between the negative terminal of the meter and the yellow test lead Press TEST button No 1 and adjust the external resistor until the external meter indicates 3 0mA Adjust R101 the Leakage Cal Control for a full scale indication on the TC28 meter 3 Insert the calibration module into socket 1 and make the following setup on the front panel selectors A B D SKT ALL UP 1 D 4 26 43465 RIOI M Fig 14 Circuit Board Layout 4 Set the TUBES TRANSISTORS Function Switch to SHORTS and adjust the me
28. itch Are all tests inoperative NO Does grid leakage check function properly NO Check junction of CR107 and CR109 for 14 volts Is the proper voltage present NO Check power trans former outputs NO Check R127 R128 and contacts on SW4 Check calibration action of R132 29 YES Check the 8 2 volt pow n er supply on drain of TR103 Is the proper voltage present YES Check TR103 with FET tester Check R129 R130 R132 R133 R136 and R10 Check contacts on SWA Check meter YES Check CR106 CR107 CR109 C115 C117 and replace as necessary YES Does emission test function properly continued on next page YES NO Does shorts test function properly Check power transformer voltages Check R2 R9 and re place as necessary Check C110 and R103 and replace as necessary YES NO Check C105 C109 CR102 CR103 R104 R105 and replace as necessary Complete the calibration procedure TRANSISTOR GAIN TEST INOPERATIVE Check test leads by shorting all three leads switch ing to leakage and pressing all 6 buttons in sequence Do all buttons indicate full scale YES NO Connect a known good transistor to the TC28 green lead to emitter yellow lead to base and red lead to collector Select the correct polarity and press button 1 Ar
29. marized in Figure 5 ICBO Button 1 ICBO is the leakage current that flows in a transistor when a voltage is applied between the collector and base with the emitter open and the collector base junction reverse biased Collector positive with respect to base for NPN transistor Its effect is similar to grid leakage in a tube in that even a small amount will upset the DC bias in the circuit In FET this leakage is called IGDO and its effect on the DC bias of 15 the circuit is even greater than for transistor ICBO When making this leakage measurement press the button carefully and note any up scale deflection of the meter Even a very small up scale deflection should be cause to reject a small silicon transistor or FET Larger silicon and small germanium transistors may safely indicate up to 50uA leakage while some special high power germanium transistors may indicate up to 3 000uA and still be within manufacturers specifications IBEO Button 2 IBEO transistors 1s the current that flows through the forward biased base emitter junction Base positive with respect to the emitter for an NPN transistor This button should produce a full scale indication for transistors For FET s this leakage would be called ISGO and indicate full scale for junction FET s and zero for MOS or IG FET s IECO Button3 IECO is the leakage current that flows a transistor when a voltage 1s applied between emitter and collector with the
30. ollector positive with respect to emitter for an NPN transistor Excessive ICEO will cause a transistor to operate unreliably in any circuit however the transistors most prone to this type leakage are high power types such as those used in audio output circuits and power supply regulators FET s this current would be called ISDO and should indicate full scale because of the normal conduction of the low resistance source drain channel IBCO Button 6 in transistors Base positive with respect to the collector for an NPN transistor 1s the current that flows through the forward biased base collector junction This button should produce a full scale indication for transistors For FET s this leakage would be called IDGO and indicate full scale for junction FET s and zero for MOS or IG FET s TYPE OF DEVICE BUTTON 1 BUTTON 2 BUTTON 3 ICBO IBEO IECO GDO SGO DSO Small Si Transistor 0 1uA 3000uA 0 1uA Large Si amp Small Ge Transistor 1 50uA 3000uA 1 50uA Large Ge Transistor 10 3000uA 3000uA 10 3000uA JFET OuA 3000uA 3000uA MOSFET QuA OuA 3000uA BUTTON 4 BUTTON 5 BUTTON 6 IEBO IBCO GSO SDO DGO Small Si Transistor 0 1 0 1uA 3000uA Large Si amp Small Ge Transistor 1 50uA 10 500uA 3000uA Large Ge Transistor 10 3000uA 100 3000uA 3000uA JFET QuA 3000uA 3000uA MOSFET OuA 3000uA Fig 5 Maximum Leakages for Good Transistors CHECKING DIODES The leakage test on the TC28
31. on adjustment to set the full scale leakage sensitivity at 3000uA The emitter lead is disconnected from the circuit by one section of SWAJ 24 5V SW4B Rili RII2 5V TO COLLECTOR MI SW4G NC TO EMITTER W4J NCe 3 Fig 12 Leakage Test Circuit SERVICING THE TC28 DISSASSEMBLY INSTRUCTIONS To remove the TC28 from its case for adjustment of the internal cali bration controls or to facilitate service merely remove the four screws from the back of the instrument case The front panel may now be lifted from the case exposing all circuitry for calibration or service All of the circuitry except for the point to point wired switches sockets has been contained on the one printed circuit board The board may be easily removed by simply unplugging the keyed molex connectors and removing the two screws that hold the board in place To re assemble the TC28 merely reverse the above procedure 25 CALIBRATION 100 Meg 4 22 MEG and CRI 1 12 MEG in series R2 270K 1K 1 010 TUBE BASE OR OCTAL PLUG Fig 13 Calibration Module The TC28 Hybrider should seldom need calibration However should you desire to periodically check the TC28 calibration accuracy thereby insuring its top performance the calibration module described above in Figure 13 is recommended The module can be constructed on an octal plug or discarded octal tube base and is to be insert
32. op in emission generally indicates a short life expectancy FILAMENT WARM UP TIME When replacing a costly horizontal output tube in a television receiver it is a good idea to not only check the horizontal oscillator for emission and other standard tests but to also check the length of time it takes to warm up If the horizontal oscillator tube is slower in warming up than the output tube the output tube will draw heavy current and its life will be shortened considerably Checking the warm up time of the oscillator tube and making sure that it is as fast or faster than the output tube can reduce the chance of a call back later for the same trouble and keep your customer s confidence high in your service ability FILAMENT VOLTAGE SENSITIVITY Some tubes may check good on the emission test and pass the other tests in the Hybrider but still not operate properly in the receiver These tubes may have a filament sensitive cathode This means that the emission from the tube will change with a change in the applied filament voltage to the tube This is caused from a low power line or defective power transformer in the receiver This type of tube can be most troublesome in series string receivers To test for this trouble simply push the LIFE TEST switch while monitoring the emission of the tube on the meter A good tube will not change its reading at all while a filament sensitive tube will drop in emission If the tube falls into the questionable
33. ormal replace IC2 SERVICE AND WARRANTY You have just purchased the finest amplifier tester on the market today The Sencore TC28 has been inspected and tested twice at the factory and has passed a rugged use test by our Quality Assurance Department to insure the best quality instrument to you If something should happen the TC28 is covered by a standard 90 day warranty as explained on the warranty policy enclosed with your instrument Sencore has six regional offices to serve you Instruments to be serviced should be returned to the nearest regional office by UPS if possible Parcel post should only be used as a last resort Instruments should be packed with the original packing materials or equivalent and double boxed to insure safe arrival at the regional office The display carton IS NOT an acceptable shipping container When returning an instrument for service be sure to state the nature of the problem to insure faster service If you wish to repair your own TC28 Hybrider we have included a schematic trouble charts and parts list Any of these parts may be ordered directly from the regional office nearest you We reserve the right to examine defective components before an in warranty replacement is issued SENCORE REGIONAL OFFICES East Central Sales amp Service Central Sales amp Service 4105 Duke Street 2711 B Curtis Street Alexandria VA 22304 Downers Grove IL 60515 A C 703 751 3556 A C 312 852 6800 TWX 710 832
34. provides a simple accurate method of determining the front to back ratio of a diode or rectifier The test switches allow measurement of both forward and reverse currents with no need to reconnect the diode 1 Set the TUBES TRANSISTORS Function Switch to the NPN LEAKAGE position 17 2 Connect the red test lead to the anode of the diode and the yellow lead to the cathode 3 Press button number to measure the forward current The for ward current should indicate at or near full scale 4 Press button number 6 to measure the reverse current The leakage current should indicate at or near zero on the leakage scale CIRCUIT DESCRIPTION THEORY OF OPERATION TUBE TEST RIO Fig 6 Tube test Bridge Circuit The basic circuit of the tube test section of the TC28 Hybrider shown in Figure 6 is a balanced bridge meter amplifier circuit consisting of FET TR103 and the combination of R136 and R10 These resistors represent an adjustable voltage that takes the place of the second FET normally needed for the bridge circuit The METER ZERO control R10 on the front panel is just like the zero controls of a VI VM and balances the circuit so that with no signal input the meter reads zero When a voltage is impressed on the gate of the FET TR103 the bridge 16 unbalanced and the meter will read in proportion to the applied signal 18 EMISSION TEST R2 R3 gt 20V gt R4 D gt R6 F R7
35. rider to a grounded source of 105 to 125 volts 50 to 60 Hz AC power 2 Locate the tube type to be tested in the setup chart Looking to the right of the tube number observe the setup information for the controls labeled A B C D and socket Some tubes have more than one listing indicating that the tube has more than one section to be tested Each section of the multiple tube is tested separately 3 Push the PIN ELIMINATION switches listed under A down to elim inate those pins If none are listed leave all switches in the up position 4 Set the B C and D switches to the positions indicated and insert the tube into the socket listed Where more than one setting 15 listed make the emission and grid leakage test on each section The shorts test need be made only once SHORTS TEST Set the TUBES TRANSISTOR Function Switch to SHORTS and check the front panel METER ZERO adjust to ensure a 0 indication on the meter Allow a period of time for the tube filament to warm up then rotate the D switch slowly through all of its positions while observing 6 the meter If no short exists the resistance of the short is greater than 200 000 ohms the meter will remain the GOOD area of the GOOD BAD SHORTS scale Shorts of 200 000 ohms or less will be indicated to a relative degree on the SHORTS scale Tubes having a directly heated cathode those in which the filament serves as the cathode will show a direct short between heater and c
36. rload for sensitive meter and circuitry SPECIFICATIONS DEVICES TESTED Devices tested Tubes transistors diodes single gate FET s TUBE TESTS Emission Load currents to 120mA and maximum applied voltage of 40 VAC RMS Grid Leakage 100 Megohm or less reads BAD 100 Megohms to 200 Megohms reads in questionable area Shorts 200 000 ohms or less 40 VAC RMS applied voltage indicates short on meter TRANSISTOR TESTS Gain IN or 5 volts VBE 3 volts peak to peak zero OUT of reference 2K Hz frequency GOOD BAD meter Circuit indication plus audible chirp for good test indication Leakage OUT 5VDC applied voltage meter indicates 0 3000 of circuit only microamps leakage current SIZE 14 X 12 X 4 POWER 105 125 VAC 50 60Hz REQUIREMENTS CONTROLS GENERAL OPERATION TUBES TRANSISTORS FUNCTION SWITCH This rotary switch applies power to the TC28 selects tube or transistor tests and the type test to be made METER ZERO This control 15 used to set meter to zero previous to making any test CONTROLS RELATED TO TUBE TEST A SWITCHES These slide switches switched to the down position serve to isolate extra connections to the tube which would falsely indicate a shorted condition The slide switch labeled RESET instantly clears all pin elimination switches FILAMENT or B SWITCH This rotary switch sets the proper fila ment voltage for the tube being tested LOAD or C SWITCH This ro
37. roblems in the circuit First check the schematic for resistors of less than 100 ohms or electrolytic capacitors of 50mF or more connected between the transistor base and collector If these are not found check the circuit board for the possibilities of Shorted foils on the board or resistors or capacitors connected to the transistor which may have changed value or become shorted GOOD READING ON ONLY ONE BUTTON good FET s and most good transistors will show a GOOD gain reading when either of two buttons 1s depressed However there are a few transistors such as Darlington pairs or devices with protective diodes between emitter and collector that will read good on only one button If an in circuit transistor shows GOOD gain on only one button it may indicate a leakage condition Therefore it is recommended that such a transistor be removed from the circuit and tested again both for gain and leakage If the transistor gives a GOOD reading on only one button and does not show excessive leakage when tested out of circuit the transistor 1s good and 1s probably one of these special types Form 1281 TC28 MANUAL ADDENDUM Please note these changes to the TC28 Hybrider manual Form 959 Mark the following sections in the manual Revised Refer to Addendum and use these instructions Page 13 Determining Basing If the device being tested checks good on two of the test buttons it is either a standard transistor or an F
38. s 2 Connect the TC28 to a source of 105 125 volts 50 to 60Hz AC power 3 The test cable is located in the lead storage compartment Connect the test leads to the leads of the device to be tested If the device to he tested is a plug in type and can be removed easily you may use the tran sistor socket located on the socket panel in place of the test cable It is not necessary to determine basing of the device the automatic test circuit will accomplish this 4 Press each of the six test buttons in turn If no audible chirp is heard and meter does not indicate in the GOOD area of GAIN EMISSION meter scale select the opposite polarity on the TUBES TRANSISTORS Function switch and press the six test buttons again If audible chirp is still not heard the device being tested is bad If the device tests bad in circuit it should be removed from the circuit and retested before a re placement is installed A good FET and most good transistors will give a GOOD indication on two of the test buttons If the exact basing of the device under test is desired refer to the section of this manual on Determining transistor basing Some special devices such as Darlington amplifiers or diode protected transistors will test good on only one test button Refer to the table in Figure 3 to determine the basing of these devices There are some rare cases where a good transistor may test BAD by the Hybrider when testing in circuit This will occur for a
39. signal coupled into pin 4 of IC2B IC2A is simply connected as an inverter so that it s output from pin 3 is in phase with the collector signal IC2B is then used as a NAND gate that is it will produce a zero output only when the two 23 5V 3 R4 RUT 2 CRII2 2 5 Cll 5 46 LR UU FROM RI23 1 5V 4 F Ki ICIC 2 CRIO4 IC2B C CRIOI FROM RI25 Y 44 xoc ICID CRIO5 pog SW4F Fig 11 Logic Circuit and Indicator Drive Schematic inputs are positive Finally IC2C is used as an inverter so that it s output is positive only when the input pin 12 is zero This pulsating positive output from IC2C is used to drive the meter and the speaker transistor TR102 A bad transistor will not yield an out of phase collector signal for pin 4 input of IC2B IC1D is biased such that it s output is zero when there is no input signal from the collector of the transistor under test This zero level is coupled to pin 4 of IC2B and makes the output at pin 6 positive The output of IC2C is then zero which indicates BAD on the meter LEAKAGE TEST The collector lead of the transistor under test is connected through R111 and R112 to plus or minus 5 volts by one section of SW4B as shown in Figure 12 The base lead of the transistor under test is connected to ground through SW4F or SW4G and indicates the leakage current through the transistor CR101 provides meter compression and R101 is a calibrati
40. tary switch determines the range of load current to be carried by the tube during the emission test 3 ON Ce ia Pn FUP Loo 10162 4 MieHTy MITE a 6 1228 amp Ion etos LJ Tyas Pav ees ane t Fig 1 TC28 The Hybrider SETUP or D SWITCH This rotary switch selects the control grid for the emission test It also serves as the shorts test switch for any inter electrode shorts by rotating the switch through its positions LIFE TEST This slide switch provides a test of the useable life of a tube by measuring how well the tube performs with a reduced filament voltage CONTROLS RELATED TO TRANSISTOR TEST TEST SWITCHES These six pushbutton switches apply the test voltage to the elements of the device under test and mechanically rotate lead connection to all possible basing configurations thus eliminating requirements for basing or circuit information CONNECTIONS A socket panel provides a total of 13 tube sockets plus 1 transistor socket for all test conditions A test lead cable terminat edin 3 EZ Hook connectors facilitates in circuit transistor or FET gain and leakage tests OPERATION TUBE TEST SET UP Operation of the TC28 Hybrider has been designed for simplicity speed and accuracy All that is necessary to completely check a tube is to follow the basic test procedure outlined below 1 Connect the TC28 Hyb
41. ter to zero with the front panel METER ZERO control 5 Switch to the GRID LEAKAGE position on the Function switch and adjust R132 the Grid Leakage Cal Control until the meter reads between the and BAD on the GRID LEAKAGE scale on the meter 6 Switch back to SHORTS and recheck the meter zero Adjust front panel METER ZERO control if necessary 7 Repeat steps 4 and 5 as required to achieve continuity 8 Change the setting of the SETUP or D switch from position 4 to position 3 9 Set the TUBES TRANSISTORS Function Switch to EMISSION and adjust R 103 the Emission Cal Control until the meter indicates on the EMISSION GAIN scale of the meter 27 10 Switch back to the SHORTS position and recheck the meter zero Adjust front panel METER ZERO control if necessary 11 Repeat steps 9 and 10 as required 12 Change the setting of the SETUP or D switch from position 3 to position 5 13 With the TUBES TRANSISTORS Function Switch in the SHORTS position adjust R105 the Short Cal Control so that the meter indicates on the line between GOOD and on the GRID LEAKAGE SHORTS scale of the meter 14 Change the setting of the SETUP or D switch from position 5 to position 7 and observe that the meter indicates zero Adjust the front panel METER ZERO 1f required 15 Repeat steps 11 through 13 as required 28 TROUBLE CHARTS TUBE TESTS INOPERATIVE Checks operation on all three tube tests on the function sw
42. tput of the peak to peak detector is filtered by C108 and C109 and presented across CR111 and R105 CRIII prevents an upscale meter indication with no short pre sent at the tube elements by blocking DC voltages of less than 0 6 volts The output of the detector greater than 0 6 volts DC is applied to the gate of TR103 through SW4D The increased DC level at the source of TR103 causes the meter to indicate up scale in proportion to the severity of the short R105 at the detector output is a calibration control that establishes the sensitivity of the test such that a shorting resistance of less than 200 000 ohms will indicate BAD on the meter THEORY OF OPERATION TRANSISTOR TEST GAIN TEST The operation of the TC28 transistor gain test represents a unique approach to the testing of transistors and FET s The test depends on a good transistor or FET providing a signal polarity reversal from input to output when operating with the emitter or source common Refer to the TC28 Schematic and Parts List insert for this brief description of overall test circuit operation A 2KHz square wave is generated by IC1B and through an emitter follow er TR101 and TR104 is coupled to the base or gate of the device under test by the test switches The test switches ground the emitter or source and also connect a positive 5 volts from the power supply to the collector or drain If the device under test is good the collector signal voltage developed at the junction
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