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Master Service Manual

1. Service Manual 7 1 3 There is a sort of display with rolling lines and or diagonal stripes Check the MA and RA lines from the 6845 CRTC 1C22 There are 14 MA lines from MAO pin 4 to MA13 pin 17 inclusiv There ar 4 RA lines from RAO pin 38 to RA3 pin 35 inclusive RA4 is not connected These lines form the video RAM addresses in the various screen modes Check that they are not stuck and that they oscillate between good logic 0 and logic 1 voltage levels If not then first replace the 6845 then look for shorted tracks Check that all are getting through to the CRTC MUX IC31 2 Check VSYNC pin 40 IC22 This line should pulse low every 20ms 3 Check HSYNC pin 39 IC22 This line should pulse low every 64us 4 Check that CSYNC both HSYNC and VSYNC superimposed is available at 1025 pin 8 and also at pin 4 of SK9 the RGB connector 5 If the RGB display alone is not working then the CSYNC polarity for that particular monitor is probably incorrect Alter LK5 6 Check all video 7 1 4 There is a cursor stuck at the top left corner of but nothing else 016 Replace IC16 7 1 5 The screen s ACORN MOS ACORN ADFS but nothing else connections ays the screen Disconnect any second or co processor which may be fitted 2 Check all connections to and from the keyboard and keyboard encoder 1 Disconnect any second or co processor which may be fitted
2. 1 4 1 2 notS SEL 8 3 OV 4 notINX 8 5 OV 6 NC 7 OV 8 notINX 5 1 4 9 OV 10 00 11 OV 12 notSl 13 OV 14 NC 15 OV 16 notMOTOR 17 OV 18 notDIR 19 OV 20 otSTEP 21 OV 22 notW DATA 23 OV 24 notWR EN 25 OV 26 notTKO 27 OV 28 notWR PCT 29 OV 30 notR DATA 31 OV 32 notS SEL 5 1 4 33 0V 34 notRDY 8 PL3 printer 26 way IDC 25 71 26 2 1 STB 2 0V 3 PAO 4 OV 5 1 6 OV 7 PA2 8 OV 9 PA3 10 OV 11 PA4 12 OV 13 PAS 14 OV 15 PA6 16 OV 17 7 18 OV 19 ACK 20 OV 21 NC 22 OV 23 NC 24 OV 25 NC 26 NC 53 Issue 1 Master Series PL4 user port Service Manual 20 way IDC 19 20 2 1 5V 2 lt GBI 5 4 2 5 OV 6 PBO 7 OV 8 1 9 OV 10 PB2 11 OV 12 PB3 13 0 14 PB4 15 OV 16 PB5 17 OV 18 PB6 19 OV 20 PB7 PL5 1MHz bus 34 way IDC 33 1 Scenes Ni 0 1 OV 2 R notw 3 OV 4 5 OV 6 notNMI 7 OV 8 notIRO 9 OV 10 notPGFC 11 OV 12 not PGFD 13 0V 14 Not RS 15 0V 16 audio in out see LK1 17 OV 18 DO 19 Dl 20 D2 211 D3 22 D4 23 D5 24 D6 27 26 OV 27 AO 28 Al 29 A2 30 3 31 A4 32 5 33 A6 34 7 54 Issue 1 Master Series Service Manual PL6 TUBE 40 way IDC 9 1 4 2
3. bypa This link application LK17 Not LK18 plug Select Two When fitted appear in e When fitted 7 may be plugged in O present the lum ision signal fitted It is nance information luma trap provided for those made West Paged ROM RAM position link in the West posit ach of the sideways in the East posit to socket labelled 1C41 inance is not required information from the ion this link causes 16Kbyte of RAM to memory slots 6 and 7 ion a 32Kbyte ROM occupying slots 6 and 10 Issue 1 Master Series Service Manual LK19 plug made West Paged ROM RAM Select Two position link When fitted in the West position this link causes 16Kbyte of RAM to appear in each of the sideways memory slots 4 and 5 When fitted in the East position a 32Kbyte ROM occupying slots 4 and 5 may be plugged into socket labelled 1C37 LK20 Not present LK21 plug not made Light Pen Strobe to cartridge This link is not normally made so position B10 on the cartridges is merely a connection from one to the other When the shunt is fitted the CRTC Light Pen Strobe input is connected to B10 This is to facilitate GENLOCK and an alternative LPSTB connection to the rear analogue connector 11 Issue 1 Master Series Service Manual 5 Hardware d
4. uses to work at all Service Manual connector and power connector are if possible to eliminate the chance of a 4 Check that the 1770 1772 and 7415174 have valid logic 0 levels at their device select inputs IC3 pin 1 and ICA pin 1 and that all data and address bus connections are present with no open or short circuits If either IC is not being selected then check the outputs on the IO controller IC15 pin 1 FDCON and pin 4 FDC If these signals are not available then check that the disc software is fitted and is selected 7 8 2 The driv 8 Fes 1 Has the correct f ct light comes on iling system for the disc been selected You cannot read a catalogue i e ADFS wiggling when to it from the disc drive on the 1770 1772 disc IC19 pin 4 and normally low but going high Say this line is not shorted to power produces a high 2177071779 If IO Controller to hold or DFS 2 Is the disc formatted 3 Is the disc in the right way round 4 Is the Read Data input to the 1770 1772 IC3 pin 19 you attempt to read the disc If not then check the signal cable and if necessary check that data is getting on 5 Are the pull up resistors R1 R3 R5 and R6 inputs fitted and correct 6 Is the 8MHz input to the
5. 1 OV 2 R notw 3 0V 4 2E 5 OV 6 notIRQ 7 OV 8 notTUBE 9 OV 10 notRS 11 OV 12 DO 13 OV 14 DI 15 OV 16 D2 17 OV 18 D3 19 OV 20 D4 21 OV 22 D5 23 OV 24 D6 25 OV 26 D7 27 OV 28 AO 29 OV 30 Al 31 5V 32 A2 33 5V 34 A3 35 5V 36 A4 37 5V 38 NC 39 5V 40 NC 55 Issue 1 Master Series Service Manual PL11 and PL24 keyboard 2x15 pin molex PL 6 BAT RO R6 R7 R2 R1 CO EZ c9 c4 ES O14 Lo TO UB CO N ES Q Fe PL24 Hr C8 C7 C3 cl R5 R4 R3 e SHIFT LOCK CAPS LOCK POWER S KBD SW OVB 5VB p H E H p H p H p H O14 WNF OO Oo WW NH p H 56 Issue 1 Master Series Service Manual Parts list TEM PART NO DESCRIPTION OTY REMARKS 1 0243 000 BARE BOARD ISS 1 1 2 0143 000 ASSEMBLY DRAWING 1 PER BATCH 3 4 0201 647 C VIDEO PROCESSOR 1 1082 5 0201 648 C SERIAL PROCESSOR 1 ICA8 6 7 0201 796 PCB REAR PANEL 1 9 10 0201 843 C EROS 1MB ROM 1 IC24 11 0201 844 C MSI KEYBD ENC CF30047 1 1C16 12 0201 85 C MSI P B C CF30049 1 1021 13 0201 846 C MSI CRTC MUX CF30048 1
6. Centronics Printer Port Connection is provided for the standard parallel printer port configuration User Port The user port is an eight bit bidirectional bus with two extra handshaking serial lines These are unbuffered RS423 A serial RS423 port is provided Audio Output The output from the sound generator is amplified to a Speaker and provided at a phono style connector Sound transfer to and from the modem is provided Modem Connection for a modem with both dial pulse and dual tone multi frequency dialling is provided This facility is provided to support third party hardware 153 Issue 1 Master Series 5 2 Core machine Service Manual Operation of the RAM and ROM is controlled by the Memory Controller integrated circuit The principal function of this control the memory paging structure Memory Map device is to The 65C12 can directly address 64K locations As over 1 2 Mbyte may be 7 resident depending on the users configuration implemented to allow access to it The basic memory assignment is as follows rn en m a mom cm dde dum m A mm ode Figure 1 14 amp FFFF amp FFOO lt amp FE00 amp EO00 amp C000 lt amp 9000 lt amp 8000 lt amp 3000 Memory Mapped 1 0 a paging scheme is Issue 1 Master Series Service Man
7. made East Two position link LK5 PCB track polarity future chip must be CSYNC this link It synchronisation polarity wire used to mak th oth synchronisation The polarity of the composite synchronisation signal versions of the directly circuit board operated by the is determined by is supplied as a track o This track must r side n the PCB causing negative be broken and a piece of f the link for positive Issue 1 Master Series LK6 0 Mul and LK6 1 ti function This group of 4 pins can tak ollows TT by Li nk between plug link nk between A and on board circuitry B and D B The comput made A B ither on Service Manual Main Clock Select ter main 16MH or two shorting plugs as 45 reference is provided This is normally how computers are shipped 16 MH reference must be The computer main provided from pin Al7 on either of the cartridge connectors Note that in could be destroyed E signal and from the computer also supplied B must also be fitted LK7 PCB track made polarity The polarity of the video RGI is supplied as This track must West for negative polarity LK8 Not LK9 Not Two position link when used with NTSC VHF televisions channels the UK is LK11 No LK D
8. cd c4 NN Mox NSS CN s OY 5 OO 10 MYM OO si DD 9 10 s O Oy 1 LO OO XO s LO M M S MONO s 1 f OO LEX N O N Sl N O N N N O N O N Y N N N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N AN c4 c4 CN c4 60 c M 10 TM N LO Y M N LO LO 1 XO LIN 10 XO 0 9 XO 10 LO LO SO 10 10 10 NN O NM HU SO OO OO HN M TWD cd ced cd cd 1 16 17 18 19 40 41 42 43 44 45 46 47 48 34 39 36 37 38 39 Issue 1 64 49 Master Series Service Manual R nos Location Sheet 50 575 1 51 7 4 1 52 0 9 53 0 8 1 54 7 5 55 72 5 1 56 TAS 1 1 58 6 6 1 59 6 5 60 6 4 6 5 1 61 62 6 7 1 63 64 6 2 1 65 3 8 1 66 70 2 67 35 3 1 68 7 8 1 69 7 6 2 70 4 3 2 71 7 6 2 32 7 6 2 73 7 6 2 74 7 5 2 75 7 8 1 76 YA 2 77 Ld 1 78 Ty 1 79 80 8 7 2 81 8 6 2 82 9 9 2 83 8 6 2 84 7 7 1 85 Lgl 1 86 87 TET 1 88 855 2 89 7 7 1 90 7 7 1 91 8 6 2 92 8 6 2 93 94 7 8 95 8 8 96 8 6 97 98 8 6 1 99 65 Issue 1 Service Manual N Issue 1 66 Location Sheet Master Series nos CN CN CY cd CN CN CV CN ANNAN CY CN Cd ee cd cd cd ed cd ed cd cd deo 1 1 1 A1 A cd ed cd CN CY LO XO Li LO OO XO XO LO OO NN CN tM CO 1 00 90 cp Pe Pei EN peo
9. 2 Try typing CTRL F BREAK drive and put an ADFS disc in it or type configure nodir RI Turn the power on 3 The configuration memory may have been set power off and on again whilst hol EAK All previous con Turn the press CTRL F to zero BR E TURN and off 34 E incorrect f this works then either connect up a disc The machine should now work y or is faulty lding down the R key Then iguration commands will be reset Issue 1 Master Series 6 logic Pediat 2 Check that the BASIC is pri 08 The BASIC prompt gt appears Service Manual nted on the screen but no gt prompt appears Disconnect any second or co processor which may be fitted 1 Check the address and ship select lines of the system VIA IC8 2 Check all 3 If all else fails then try a different keyboard for broken leads and tracks on the original one 4 Check that memory cont connections to the be used to Note time it occurs the occur if some othe troller isolate it the IRQ connections to the keyboard encoder IC16 IRO line on the CPU IC14 pin 4 is not stuck in one state If it is then check the address and chip select the system VIA lines of but the keyboard does not respond If this works loo
10. AS IC11 pin 14 low DS IC11 pin 17 low 4 Check that R W IC11 pin 15 wiggles when alternate reads and writes are performed 7 1 10 The computer powers up in terminal mode and configure will not change it 1 Check 1 and 2 in the section above 2 Check all connections to the clock RAM chip IC11 for open circuits or short circuits 7 1 11 The computer works but random dots or characters appear on the screen Type a short program or piece of text into the machine about two lines in any screen mode are adequate Leave it for a few minutes and then see if the screen has been corrupted If it has then there is a memory system fault If it hasn t then enter a longer piece of program 47 or text enough to fill a screen and repeat the test Any fault showing itself will be due to a memory system failure These are rarely due to the RAM chips themselves as these are usually very E reliable Check the following very carefully 36 Issue 1 Master Series Service Manual 2 Check all connections from the CPU address bus IC14 pins 9 to 20 and pins 22 to 25 inclusive to the DRAM address multiplexers ICs 29 30 and 33 voltage leve Signals shoul 3V for 1 A power rail 3 Check that 15ns after edge see period of th active low pe E fi ls of these signals at the multiplexer Poor logic levels imply shorting to anot
11. RAS goes low and changes no later than 50ns after that e system 2MHz clock out of the VI Then check the input pins All less than 1V for 0 greater than implies a short to the relevant ther logic signal see circuit diagram for pin numbers d have good CMOS levels constant 0 or 5V level least the address at the DRAM inputs is stable for at gure 8 This should occur once for every active high DPROC and once for every riod 4 Check 500mV that TE Ju the noise around logic LOW signals is generally less than is not then some signals may be shorting or a decoupling capacitor may be missing 5 Check tha the DRAMs 7 1 12 You can type but ge 1 Check Test the data bus is properly connected b n the CPU and CW t two or more copies around the screen Points TP7 to TP20 the CRTC scanning outputs shown on circuit diagram to the left of the CRTC IC22 to make sure that the correct addresses are being generated Any line stuck high or low or shorting to another pin will give strange screen effects Note MA13 1022 pin 17 is used to switch the address multiplexing circuits between modes 7 135 and any other modes This line should be static in any given mode 2 Check that all of the lines from the CRTC 1022 to the CRTC Multiplexer IC31 actually get there 3 Check tha
12. Ri 1Qu 6v3 2e Sy 5 t pc At 16v 232 0 7 Keyboard circuit diagram CTRL 2 SHIFT 75 OO L A q qq eS ee A A A AAA ee rm a nr nn eee 18 7 1 POWER ON 2 CAPSLOCK 3 SHIFT LOCK 4 5 2 y COPY 0 RETURN r gt NOTE ALL PRIMED KEYS ARE N NUMERIC KEY PAD
13. in the Issue 1 Master Series Service Manual Does it only occur on one of the video outputs 1 Is the CSYNC polarity link LK5 correct for your monitor 2 If it only occurs on composite video check that all the resistors R147 to R150 inclusive to the output transistors are correct in accordance with the circuit diagram Do they all have good signals going into them 3 If it only occurs on UHF check the signal as it passes through the resistor network IC40 pins 12 to 19 inclusive through resistors R69 75 77 78 84 85 87 and 89 7 3 3 There is no colour on UHF Is the variable capacitor VC2 set to give the correct frequency of 17 7345MHz at IC43 pin 12 2 Check connection to IC40 pin 11 and resistor summing node through Li and C81 Q12 c88 and R140 3 Check 5V supply on IC40 pin 20 4 Try replacing IC40 as a last resort 7 3 4 There is only one colour On RGB 1 Check the RGB connections out of the VIDPROC IC42 pins 14 12 and 10 2 If the fault is only in mode 7 or 135 then check RGB connections from SAA5050 IC32 pins 24 23 and 22 to the VIDPROC IC42 pins 13 11 and 9 On UHF 1 Check RGB inputs to IC40 pins 6 7 and 8 If there are any faults check the connections from the VIDPROC IC42 pins 14 12 and 10 If any nodes are stuck at 5V or ground then check for sh
14. 125 R115 R74 R82 R17 855 138 139 141 144 152 R85 8116 R68 94 95 R92 101 R112 RP1 2 c15 17 60 c21 032 49 C11 C9 12 35 C40 43 C47 C55 56 Issue 1 97 98 99 10 1 pa po po pa po TH oO OOO C O 0 0 TEM N o D ho NN DN Owe NA N 12 12 13 13 13 13 13 13 13 13 13 150 1 I GO O amp H WNE OQ o 8 9 0 1 2 3 4 5 7 8 9 Master Series Service Manual QTY REMARKS HA H H UW Rs N Es C19 C26 C80 C6 7 83 84 C81 C23 44 45 88 92 03 85 86 C87 4 7 626 64 69 C91 C18 71 73 8209 C16 C36 04 79 0346 A CE VC2 103 1C17 18 23 26 1C32 IC12 TEA IC6 8 OPTION 1011 1C22 1C45 PART NO DESCRIPTION 0631 010 CPCTR CPLT 10p 3V 2 0631 022 CPCTR CPLT 22p 3V 2 0631 027 CPCTR CPLT 27p 3V 2 0631 033 CPCTR CPLT 33p 3V 2 0631 039 CPCTR CPLT 39 3V 2 0631 047 CPCTR CPLT 47p 3V 2 0631 100 CPCTR CPLT 100p 3V 2 0631 150 CPCTR CPLT 150p 3V 2 0631 220 CPCTR CPLT 220p 3V 2 0631 270 CPCTR CPLT 270p 3V 2 0634 010 CPCTR CPLT 10n
15. 4 Check that the Rx CLK going into the ACIA is correct 1C45 pin 3 7 7 Cassette interfac 7 7 1 Will not load or save data 1 Check the cable and data recorder with another computer if possible 2 Check that the ACIA and SERPROC have correct i e no open or short circuit connections on all pins 3 Check that the back panel connector has no dry joints or short circuits between it and the interface circuitry 42 Issue 1 Master Series Service Manual 4 Are the connector pins in good condition If not the fault could show itself as intermittent operation 5 Check the 1 23MHz connection to the ACIA 7 7 2 Will not load data 1 Check 3 and 4 above 2 Check that the ACIA is receiving an Rx CLK IC45 pin 3 2 Check the connections between the SERPROC IC48 and ACIA IC45 3 Check that incoming data is appearing at the pin at the back of the connector 4 Follow the signal path through the high and low pass filters It should finish up as a 1 2V peak to peak signal at the CASIN input to the SERPROC IC48 pin 12 If it disappears at any point there is probably a dry joint 5 The cassette data input has a static that all the components in this are fitted and have protection network on it Check the correct values A faulty component subsequently damaged 6 Check that the ACIA and S
16. Master Series Service Manual 5 Is the SERPROC getting a 1 23MHz timing reference IC48 pin25 This signal could come from either one of two Sources gt a A 74LS169 counter b The chroma chip Whichever it SHOULD come from is dependent on the build standard of the computer In any case the SERPROC should get this signal from some source Check that it is the correct frequency 6 Is the 5V supply correctly connected and working to the RS423 transmitter chip IC50 pin 8 7 Are either CTS IC48 pin 20 or RTS IC48 pin 23 stuck high or low 8 If all else fails check all remaining connections to the ACIA and ERPROC 7 6 2 Will only receive data Does the remote computer use different transmit and receive rates If so check that your computer has the equivalent receive and transmit respectively 2 Check 3 6 and 7 as above 3 Check that data going into the line driver 1C50 comes out of it The driver could be faulty otherwise 4 Check that the Tx CLK going into the ACIA is correct 1C45 pin 4 7 6 3 Will only transmit data Does the remote computer use different transmit and receive rates If so check that your computer has the equivalent receive and transmit respectively 2 Check 3 6 and 7 as above 3 Check that data going into the line receiver IC51 comes out of it
17. he LK13 track is cu logue ground ision r e arre uit dia LK14 PCB tr 48 gram ack made Serial rer As shipped this link is a track on the PCI 1 23MHz output to the Serial Processor production purposes and should not be modified LK15 renc nc VO this link is a track on ltage i track is cut then t and a erence can be fi One position link PCB track made West PA sele As shipped in the UK this link is a track on the bottom of the PCB colour information on to the If the track is cut and a wire link then colour information will televisions within the UK can only causing the CHR television ou used to make be encoded in NTSC In general ct Two position link accept the PAL format LK16 wire lin tput in PAL format the other side of the link E and Vref on Service Manual A to D converter reference select nput to be data clock L NTSC OMA chip to encode the bottom of the PCB causing the 1 8V the voltage reference must be applied the external connector LK13 made East with a wire link a tted in the position PR1 shown on the B connecting the CHROMA chip This link is provided for k not fitted Chromi Ss One position link is not normally s where filtering chrominance part of the telev
18. required Only 1 Kbyte of memory is needed for either of the Teletext modes although 20K is reserved for it in mode 135 The MOS uses the spare 19K to speed up inter filing system file transfers but the user e may use this memory if no such transfers are to be done The VIDPROC has to be re programmed to use the SAA5050 RGB outputs The 6845 is still used to generate the cursor As a delay of 2 75 us will occur after a character is read from RAM before outputting the appropriate RGB signals the 6845 has to be programmed accordingly The start of screen signal is given a 1 5 byte time offset and the SAA5050 has a further 1 byte time offset to restore the correct cursor data phase The VIDPROC has further adjustment which allows for the cursor to be adjusted to pixel accuracy Hardware Scroll Scrolling may be achieved in any mode by programming the 6845 start of screen address to an integral number of video lines further down the memory map than the nominal start of screen This of course causes th linear address generator to attempt to display an end of screen which is out of the reserved video area To overcome this effect hardware scrolling is provided with a variable address wrap around In effect when the address generator would otherwis attempt to ccess out of screen RAM its addresses are modified to point t
19. will always have the it is desirable is used to have the value E00 16 n for the variable PAGE irrespective of the current filing system Issue 1 Master Series This is achieved by providing a filing system workspace as follows Bit Y in ACCCON when set Causes 8 Kbyte of RAM referred to be overlayed on the MOS VDU drivers i e Service Manual to as HAZEL from C000 to amp DFFF responsible for resetting the Y bit as no this purpose The remaining bits in ACCCON are used to control various peripheral systems The bit ITU in ACCCON when set enables th Clearly when this bit has been set no calls may be made to the MOS for VDU operation The code which performs this paging operation is hardware is provided dE or CPU to access the internal second processor rather than the external one The bit IRR in ACCCON is InterRupt Request When set causes an open drain output to pull the CPU ROMSEL this bit NIRO pin down to Vss The contents of ROMSEL determine the paging of memory in the 16K region amp 8000 to amp BFFF One of sixteen unique 16 Kbyte ROM memory segments may be selected One additional 4 Kbyte RAM segment may be selected from amp 8000 to amp 8FFF Eight of the segments are assumed to be in lower segments Seven of the segment
20. 1031 14 0201 847 C MSI I O CTRL CF30050 1 15 16 2201 21 C MSI CHROMA CF30060 1 1040 17 2201 213 C MSI MEM SW CF30058 1 IC20 18 19 20 217 22 23 0502 100 RES 108 C MF 5 OW25 4 R27 37 38 113 24 0502 101 RES 100R C MF 5 5 4 R48 49 57 58 25 0502 102 RES 1K0 C MF 5 5 17 3 33 34 43 47 51 54 56 75 117 122 133 137 145 148 150 151 26 27 28 0502 103 RES 10K C MF 5 0W25 18 R8 14 18 21 23 28 29 32 53 71 81 83 102 109 6 0 29 30 31 0502 104 RES 100K C MF 5 0W25 5 R10 22 24 0 32 0502 105 RES 1MO C MF 5 5 2 R46 155 33 0502 122 RES 1K2 C MF 5 0W25 3 R77 78 89 34 0502 151 RES 150R C MF 5 5 5 R1 3 5 6 59 35 0502 152 RES 1K5 C MF 5 5 3 R65 108 140 36 37 0502 154 RES 150K C MF 5 5 2 RIO 121 38 39 0502 182 RES 1K8 C MF 5 0W25 1 R69 40 41 42 0502 221 RES 2208 C MF 5 0W25 3 R44 50 121 43 0502 222 RES 2K2 C MF 5 0W25 8 R4 11 76 90 105 107 134 149 44 om Issue 1 Master Series H E N OAD 0 01 01 ds ds ds gt w N 01 O1 O1 O1 a O 005 10 61 62 63 64 65 66 67 68 69 70 del 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 PART NO 0502 223 0502 224 0502 272 0502 273 0502 274 0502 330 0502 331 0502 332 0502 333 0502 391 0502 392 05
21. 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 Service Manual PART NO DESCRIPTION OTY REMARKS 0742 174 C 74LS174 TTL 16 0 3 1 0742 244 IC 74LS244 TTL 20 0 3 1 IC5 0742 257 IC 7415257 TTL 16 0 3 1 IC30 0744 257 IC 74ALS257 TTL 16 0 3 OPTION 0742 259 IC 74LS259 TTL 16 0 3 1 IC10 0744 259 IC 74ALS259 TTL 16 0 3 OPTION 0742 373 C 7415373 TTL 20 0 3 1 IC7 0744 373 IC 74ALS373 TTL 20 0 3 OPTION 0748 000 IC 74F00 TTL 14 0 3 1 IC36 0748 074 IC 74F74 TTL 14 0 3 1 IC28 0749 253 IC 74HCT253 CMOS 16 0 3 2 IC29 33 0770 324 IC LM324 QUAD OP AMP 2 IC9 46 0770 386 IC LM386 AUDIO AMP 1 1C13 0780 177 FEAT J177 T092 30V P CHAN 1 04 0780 239 TRANS BC239 NPN 8 03 5 6 8 9 10 12 14 0780 309 TRANS BC309 PNP 2 011 13 0794 148 DIODE SI 1N4148 14 D7 10 12 13 17 24 0800 001 CONR 5W SKT DIN RA DOM 1 SK10 0800 002 CONR 6W SKT DIN RA PCB 1 SK9 0800 003 CONR 7W SKT DIN RA PCB 1 SK11 0800 004 CONR 5W SKT DIN RA PCB 1 SK7 0800 006 CONR 34W HDR IDC RA 4 WALL 2 PL1 5 0800 007 CONR 40W HDR IDC RA 4 WAL 1 PL6 0800 008 CONR 26W HDC IDC RA 4 WAI 1 PL3 0800 009 CONR 20W HDC IDC RA 4 WAL 1 PL4 0800 043 CONR 44W EDGE DS ST
22. 23 pin 5 RAS and pin 16 CAS The main DRAM timing is shown in figure 8 2 jc i naam RAS v y E gt Ons 5 q OA cas _ ko It e Il gt sons PENN 21 ENDE 7 A gt a buffers switched off VDU CPU Figure 8 DRAM timing RAS and CAS should be good 4MHz square waves If one or both is missing then check for shorted tracks Remember the DRAMs can be destroyed if RAS is stuck low RAS is generated from 4M and 8M by the D type IC28 pin 9 CAS for the main DRAMs is generated from 2M inverted by a NAND in IC34 to give phi2 IN gated with DRAMEN which enables the main RAM and finally gated with 4M through another NAND in IC34 9 Check that the auxiliary DRAM CAS line when inverted at IC36 pin 8 is low If it is high at this point then it will suppress the main DRAMs 10 Check the multiplexed address lines into the main DRAMs ICs 17 and 23 pins 6 7 8 10 11 12 13 and 14 The address lines should switch after RAS with an approximate 20ns hold time as shown in figure 8 Also check that the address lines are correctly switching after phi2 as shown in figure 8 If any of the DRAM timing is found to be out of specification then check that C26 is fitted and is the correct value 33 Issue 1 Master Series
23. 5V 80 0635 470 CPCTR ALEC 47u 16v RAD 0637 104 CPCTR CML 100n 5V 80 0637 473 CPCTR CML 47n 5V 80 0650 333 CPCTR MPSTR 33n 5V 20 0650 334 CPCTR MPSTR 330n 5V 205 0651 224 CPCTR CER 220n 12V 80 0680 002 CPCTR DCPLR 33 47n 0 2 0680 005 CPCTR DCPLR 33 47n 5Px6H 0699 001 CPCTR TRMR 2 22p 5V 0699 004 CPCTR TRMR 5 5 40p 25V 0701 770 IC WD1770 FDC 5 25 0704 105 IC 4464 DRAM 120nS 64Kx4 0705 050 IC SAA5050 CHTR GEN 0706 489 IC 76489 SOUND GEN 0706 512 IC 65C12 CPU CMOS 2MHZ 0706 522 IC 6522 VIA NMOS 1MHZ 0706 524 IC 6522 VIA CMOS 1MHZ 0706 818 IC 6818 RIC CMOS 0706 845 IC 6845 CRTC NMOS 1MHZ 0706 850 IC 6850 ACIA NMOS 1MHZ 0707 002 IC 7002 ADC 12 BIT 0709 637 IC 9637A RS422 423 RCVR 0733 691 IC 3691 RS422 423 DRVR 0740 006 IC 7406 TTL 14 0 3 0740 016 IC 7416 TTL 14 0 3 0740 038 IC 7438 TTL 14 0 3 0741 000 IC 74500 TTL 14 0 3 0741 004 IC 74804 TTL 14 0 3 0742 000 IC 74LS00 TTL 14 0 3 0744 000 IC 74ALSO0 TTL 14 0 3 0742 002 IC 74LS02 TTL 14 0 3 0742 014 IC 74LS14 TTL 14 0 3 0742 086 IC 74LS86 TTL 14 0 3 0744 086 IC 74ALS86 TTL 14 0 3 59 1089 1651 1050 101 OPTION 1C2 1C34 1C43 1C38 OPTION 1059 EELS 1025 OPTION Issue 1 Master Series TEM 151 152 153 155 156 158 159 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188
24. CARTRIBES 4 ON PORTRID wat SECTS OL 70 d H 1 i E L s ii sl LE Sere Pe Le a 33 y EI FH he dE w bx et dos pajut ger le TE je sar Fla elolalaje m Fy a E xe ST m 8 a P a 2 SET Ty WS ae a jo 7t TS etr 20 07 BAT Dl e PCB circuit diagram Sheet 2 SAS 2 amp 4 NOT FITTED ON UM 2 PS SAT OF ICA ARE RUA MODEM AUDIO 4 TUE 2 rien AAN LITTEIETC IIIIII LIL Ata 001 7741 OPE 0 mers EXFEEREEKXEEEILCLEL 1142194599 i LI oe En 4 n ipf gt M3 o 71 L RS4Z3 2 m CNN 8 5 CASSETTE suaMc 5 1 112 Lo SR Le t en Ey mm E Thor Pr Det Pin FROM ECONET MODULE 6 SiL NF 0 2 OF CM 1 ELEC nonnann ce 7 3 c 1 ABD Sw i airs xs ex m mu e Re
25. Do OV OV OV CO XO Or 0 CO T RON ON ON ON non OR nn NON ON ON ON M E RON ON ON On on on M 000000 CV O OY OO O CO OD M CN MINO OO OO CO OO 00 OO cO OC OV N CO OV Oy AO CO HN M sf LO XO 00 OY QOO c4 CON M si 10 O0 D M XO 00 OY CO cJ CN M XO 00 OY M st LO SO 00 OD M si 10 ced ced ced ced CN OCN CN CN CN CN CN CN CN ON M 00 00 00 00 00 00 00 00 5 sP SP SP SP SP SP SP SP SP LO LO LO LO LO LO cd cd cd cedo cd cd cd Cd cd cd cd cd cd cd cd cd cd cd ced cd cd Cd cd cd cd cd cd cn cd ced cd ced cd cd cd ced cd ced cd cd Service Manual Master Series Location Sheet C nos CN NN c4 CN N N NN NN NT N NN NN 00 00 O XO XO st nn LL OO LO sr M M OS OON SN MON lt es A N Z S ed 10 c4 c4 SP LO 10 10 10 SP 10 LO YN NOM 10 WM A 9 SO O00 CO c4 CN M sf OF cd ed cd cd ced cd cd cd do ft OO LO WM non OY 10 10 IN CO INN N N o N N LO N 6 d XO DO CN CN CN CN CY MOM OM o o SI m 35 Bb NN AN Iss
26. FLNG 2 SK3 4 0800 050 CONR 2W WAFR 0 1 ST PCB 4 LK4 21 60 61 0800 051 CONR 3W WAFR 0 1 ST PCB 4 PL8 LK12 18 19 0800 067 CONR 5W WAFR 0 1 RA 4PI 1 PL10 0800 070 CONR 2W SHUNT 0 1 5 LK4 12 18 19 60 0800 091 CONR 2W WAFR 1 RA PCB 1 PL9 0800 128 SKT IC 28 0 6 NORM 3 IC27 37 41 0800 203 FSTN TAB 6 3mm ST PCB 7 PL17 23 0800 304 CONR 15W SKT D RA E2 84 1 SK12 60 Issue 1 Master Series TEM 204 205 206 207 208 209 N o N NNNNN NN N o 1 01 PD H N o 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 Service Manual PART NO DESCRIPTION OTY REMARKS 0800 455 CONR 15W WAFR 1 ST PCB 2 PL11 PL24 0800 481 CONR 5W SKT HSNG 0 1 PCB 1 SK6 0800 482 CONR 12W SKT HSNG 0 1 PCI 2 SK1 2 0800 483 CONR 19W SKT HSNG 0 1 PCI 1 SK5 0800 600 CONR BNC SKT 75R PNL 1 SK8 0800 611 CONR PHONO SKT RA PCB 1 SK13 0801 200 CONR 20W 0 1 SR ZIF 4WR 1 PL12 0810 001 RLY 1P CO 5V 50R PCB 1 RL 0820 160 XTAL 16 000MHz HC18 U 1 X2 0820 177 XTAL 17 7345MHz HC18 U 1 X3 0821 327 XTAL 32 768KHz CC 0 05 1 X1 0825 000 MODUL UHF PAL WB E36 1 MD1 0860 005 COIL RF 33uH AX 0 45 1 Li 0870 420 WIRE 22SWG CPR TIN A R 14 10 0884 042 RIVET POP DOME HD 3 2mmD 4 61 I
27. locate with all the correct points on the PCB and back plate Replac the 4 PCB fixing screws which pass through the cartridge connectors and the single screw which joins the back plate to the power supply unit Reconnect the power supply being careful to route the wires neatly and connect the wires seven to the push on connectors on the PCB being very careful to get the polarity right PCB connectors marked 5V must have a red wire attached three PCB connectors marked OV must have a black wire attached three The connector marked 5V has the purple wire attached one 6 Issue 1 Master Series Service Manual Replac th speaker and battery unit first plugging the two connectors into their correct positions on the board the battery connector to PL8 either way round and the speaker connector to 9 either way round Note that although the battery connector can be plugged either way round it must locate on all three pins or the polarity will be wrong Check carefully Replace th sockets so connectors keyboard Replace the 4 screws 3 to the lower case and 1 to the power supply unit Be careful to reconnect the keyboard ribbon that all the pins are engaged it is easy to displace the one pin to right or left Make one final check that all reconnections have been made correctly especially reversed the p
28. manual All correspondence should be addressed to S Technical Enquirie Acorn Computers Limited Newmarket Road Cambridge CB5 8PD All maintenance a Acorn Computers maintenance by una assist the reader Computers shall n arising from the error or omission in product This manual is for the sole use of Acorn Comput and must only be used by them in connection wit within First published 19 86 in the use of ot be liable use of any this uthorised personnel E in nd service on the product must be carried out authorised dealers liability whatsoever for any loss or damage caused by service This manual t by Acorn Computers can accept no or is intended only to this product for any loss ormation or part or and therefore Acorn damage whatsoever ticulars in or any manual Published by Acorn Computers Limited or any ters th the product described incorrect use of the authorised dealers Issue 1 Master Series Service Manual WARNING THE COMPUTER MUST B T EARTHED IMPORTANT The wires in the mains lead for the apparatus are coloured in accordance with the following code Green amp Yellow Earth Blue Neutral Brown Live The moulded plug must be used with the fuse and fuse carrier firmly in place The fuse carrier is of the same basic colour though not necessarily the same shade
29. on the main processor to supply such information They do all the computation not associated with I O operations When a co processor is not fitted the main processor has to perform both I O and non I O computation 12 Issue 1 Master Series Service Manual External I O Video display A 6845 CRT controller is provided to format the output from ROB composite video and PAL NTSC connectors Analogue to Digital Converter A four channel A D converter provides 10 bit binary conversions in 5ms The absolute accuracy will depend on X the conditions of use Tape Interface Facilities to both save and retrieve data from audio cassettes is provided Disc Interface Facilities to both save and retrieve data from standard Shugart connected media Filing systems are provided to support data encoded in FM or MEM Network Interface Connection to the ECONET is provided by a 68B54 advanced data link controller This is fitted on a daughter board and may as such be fitted as an optional extra standard on the ET machine 1MHz Bus The standard BBC computer 1MHz bus is provided External Second Processor An external second processor may be connected Selection of either internal co processor or external Second processor is performed by software Only one second or co processor can be active at a time
30. region amp 8000 to amp 8FFF are redirected from the currently selected ROM to a region of RAM referred to as ANDY It is the responsibility of the code which set RAM to clear it after accessing ANDY This is necessary to ensure correct operation of software in ROM Summary of RAM memory map The 64K of DRAM is distributed as follows FFFF TFFF With V i H 1 gt EorX V i active 8000 i 3000 i RAM DFFF 1 ADDRESS gt With i C000 Y active CPU 9000 gt ADDRESS 1 gt i 8000 8000 RAM active I l i i i 0000 0000 Bits in ACCCON Figure 4 A further 64 Kbyte of RAM is available as four pages of 16 Kbyte from amp 8000 to amp BFFF The ROM slots 4 5 6 and 7 are not active when this RAM is link selected to be active 18 Issue 1 Master Series Service Manual 5 3 Internal 1 0 Slow peripherals These are subsystems which are provided with data from port A of the system VIA This data is stable until next programmed by the CPU Keyboard General description 93 keys are provided 92 of these are in a modified 8 x 13 matrix as shown in figure 5 A keyboard encoder 1C16 is used to scan the keyboard During idle free run mode pressing any key will cause an IRQ to be generated via the s
31. the 1 Check that the two connectors on the Econet module are correctly serted The longer connector has two spare pins on the left of the in PC 2 3 B socket ns it will not Check that Check that the NMI Econet on the module is work If the module is displaced and is plugged into one or both of these spare pi installed and fitted correctly CPU pin 6 1C14 49 TP 3 is not being held low Issue 1 Master Series Service Manual Appendix 50 Issue 1 Master Series Service Manual Connector pinouts TV UHF out phono outer ground inner UHF SK8 video out BNC outer ground inner video SK9 RGB 6 pin DIN SK10 RS423 5 pin DIN Data in SK11 cassette 7 pin DIN Motor control 55 Issue 1 Master Series SK12 analogue in 15 way D type 00000000 000000 0 5V OV OV CH3 analogue ground OV CH1 analogue ground 1 Oy O1 amp SKI ECONET 5 pin DIN 9 light pen strobe not 10 digital switch input 11 voltage reference 12 CH2 13 digital switch input 14 voltage reference 15 CHO VRE VRE Service Manual 56 Issue 1 Master Series Service Manual PL1 disc drive 34 way IDC 3
32. 02 393 0502 471 0502 472 0502 473 0502 562 0502 563 0502 565 0502 680 0502 681 0502 682 0502 820 0502 822 0502 824 0590 222 0611 047 0611 100 0611 470 0613 100 0613 101 0629 002 0629 004 0629 010 0630 082 DESCRIPTION QTY R RES 22K C MF 5 5 1 RES 220K C MF 5 OW25 2 RES 2K7 C MF 5 OW25 3 RES 27K C MF 5 5 1 RES 270K C MF 5 OW25 1 RES 33R C MF 5 W25 3 RES 330R C MF 5 OW25 7 RES 3K3 C MF 5 W25 5 RES 33K C MF 5 25 1 RES 390R C MF 5 W25 1 RES 3K9 C MF 5 OW25 3 RES 39K C MF 5 W25 3 RES 470R C MF 5 OW25 2 RES 4K7 C MF 5 OW25 9 RES 47K C MF 5 5 1 RES 5K6 C MF 5 OW25 1 RES 56K C MF 5 5 1 RES 5M6 C MF 5 W25 1 RES 68R C MF 5 5 8 RES 680R C MF 5 W25 1 RES 6K8 C MF 5 W25 1 RES 82R C MF 5 0W25 3 RES 8K2 C MF 5 W25 2 RES 820K C MF 5 0W25 1 RES NET 2K2 TF 10 9P 2 CPCTR TANT 4u7 16V 20 CPCTR TANT 10u 16V 20 3 CPCTR TANT 47u 16V 20 1 CPCTR TANT lu0 35V 20 2 CPCTR TANT 10u 35V 20 1 CPCTR CPLT 2n2 30V 80 3 CPCTR CPLT 4n7 30V 80 2 CPCTR CPLT 10n 3V 80 1 CPCTR CPLT 820p 3V 10 2 58 Service Manuel EMARKS R36 R35 104 R88 103 131 R52 R70 R62 64 127 R40 41 42 96 97 98 100 R66 67 87 118 130 8119 R136 R132 146 147 R31 39 91 R153 154 RY 267 12 gt 13 84 1261 9
33. 1 8V across pins 8 and 9 of IC49 and has very little noise on it 4 Are all the address and data bus connections to IC49 correct 5 Are the input voltages within the range 0 to 2 5V If not the converter will not work correctly 6 Have any of the terminals in the connector been connected to voltages greater than 5 5V or less than 0 5V If so the A D converter is likely to be damaged Replace IC49 7 Is the chip select from the 10 controller IC15 pin 35 correctly connected to IC49 pin 23 8 Does 1049 have a 1MHz timing reference on pin 2 7 5 2 Gives erroneous results on just one channel 1 The plug and cable connections are the most likely sources of problems Point 6 above may also apply 7 6 RS423 port 7 6 1 Does not work at all 1 Are the data format and baud rate settings the same as the remote computer Note these will be set to the configuration values after power on or CTRL BREAK Make sure that these are correct as well 2 Is the cable properly connected Note this connector CAN be inserted the wrong way up 3 Are all the cable connections correct i e no open short circuits 1 Are the device select connections to the SERPROC and ACIA from the 10 controller correct IC15 pin 34 and pin 36 respectively with no short circuits to either power supply rail 41 Issue 1
34. 1770 1772 correct Check that it is available at IC3 pin 18 If not then trace it back to 1042 pin 7 7 Is the 1770 1772 DRQ line IC3 pin 27 once every 32us when then disc interface has been asked to read a catalogue If not then check that or ground and is connected to the IO Controller IC15 pin 5 8 Check that the DRO transitions IC3 pin 27 appear logically inverted at the NMI pin on the CPU IC14 pin 6 9 Check that the 1770 1772 INTRQ output IC3 pin 28 going pulse at the end of every command issued to the the INTRO line is shorted high it will cause the the CPU NMI line low thus masking DRQ transitions 44 Issue 1 Master Series 7 8 3 The ca 1 Some computers have 220 pF capaci ground Is this fitted Is its val on the PCB for computers that do not 2 Are one or two disc drives present two of them has line termination resistors in 7 8 4 The catalogue can be read but not the data talogue can be read but th ntri S ar Service Manual or C27 need this capacitor TE cannot be changed in ADFS corrupted fitted from the DRQ line to ue correct There will be no place make sure that only one or the directory 1 Issue 1 boards only There should be a small capacitor from the DRQ line to ground Is this fitted Is its value correct 2 Are one or two disc drives present If two make sure that on
35. 4 R i N al a Im c ms K x wi sun 8 In them 2 1 MT Ope NFT 20 b we ROUT E ELEZ ov 7 ta S La w Pus 7 T Mot E ra TPF SA TF Pi j TI had I m ot ce cn 7 Row Tp 074 f EEE AL i en b 1 A AAA A 1 WE VERSO a 5 ES qub CCT FOR FW D anms I n 5i Li Final assembly 7 Fr 10143 0 VERSION 72 EPROM cartridge circuit diagram Sy in R1 10K 73 PL1 A1 B1 6 3 A12 pe AN Bi A10 2 gs _ a A7 11 6 CAPA CERDO m 6 A BB B6 87 B8 B9 B3 B20 82 B19 Ad AAI 6 LT AAA A22 e A20 Ri B22 K 2 RW an Econet module circuit diagram SK h 3 3 ADLC 8R W uU Hcr 1 MC68854 icz 8 16 76LSi23 1 3 5 8 1 08 ice 6 11 3 NC NC NC 7H 2216098 25 530 Wi 0v R4 M 5x2 O DA DA a 1M319 100 2 t o D ws Ris ne 4 e CK ptr 4 5 8 CK 1 LM319 IM 100K Th Lx Us sv hos Ye 1K5 2 C3
36. ERPROC have circuit connections on all pins 7 Check the 1 23MHz connection to the ACI 8 As a last resort ACIA very reliable change the SERPROC 7 7 3 Will not save data could mean that the LM324 has been correct i e no open or short A and try again then try the This should not be necessary as both of these components are 1 Check the cable and data recorder with another computer if possible 2 Check that the ACIA is getting a Tx CLK 1C45 pin 4 3 Check the connections between the SERPROC and ACIA 4 Check that the back panel connector has no dry joints or short circuits between it and the interface circuitry 5 Are the connector pins in good condition If not the fault could show itself as intermittent operation 6 Check that data is coming out of the CASOUT output from the SERPROC check all the data and address connections to the from the SERPROC to the connector IC48 pin 27 If not SERPROC and ACIA 7 Follow the signal if it exists If it disappears then a dry joint or short to power or ground is likely 43 Issue 1 Master Series 7 8 Disc drive interface 7 8 1 Ref 1 Check that both the signal securely pushed home 2 Try another disc drive if possible fault in this 3 Try the disc drive with another computer
37. VIA 31 Issue 1 Master Series 7 1 Switch on Service Manual If the suspect microcomputer has a second or co processor fitted then disconnect it Connect the suspect microcomputer to a UHF TV and an RGB monitor connecting both a TV and a monitor will show up any fault in the connecting leads or the polarity of CSYNC Connect the mains supply and switch on both the monitors and the computer One of the following will happen 7 1 1 There is noise on the monitor screens no signal from computer There is no power on beep sound and the keyboard power indicator does not light Results the power supply is dead Follow the sequence of checks shown below 1 Check the power supply see 7 2 Try replacing the power supply anyway as the fuse may have blown 7 1 2 The power supply is working the keyboard indicator is lit but nothing else happens Results There is a board fault Follow the sequence of checks shown below 1 Check that all ICs have power and ground on the correct pins at the correct voltage Make good any dry joints 2 Feel whether any of the ICs are hot Check for shorted PCB tracks Watch for shorts from 5V to the IO controller causing it to latch up Clear shorted tracks and then replace any affected ICs Note ICs which get abnormally hot due to a fault but which work after the fault has been
38. a Acorn The choice of experience British Broadcasting Corporation Master Series Microcomputer Service Manual British Broadcasting Corporation Master Series Microcomputer Service Manual Part No 0443 004 Issue 1 April 1986 Master Series British Copyright Neither the whole or any part of the information contained in ual may be adapted or reproduced in any prior product described material form Computers Limited in except ithin this publication the term B Broadcasting Corporation Acorn Computers Limit BC is used as this man with the Acorn Compu ters ted 1986 written The product described in this manual and products subject to a technical including the information and part Acorn Computers in good fait errors or omissions may be Ez ticulars continuous development and improvement nature and particulars of the product and in this However in this manual amendments from Acorn Comput or revisions to ers Techn ical Enquiries A it is ackn list Service Manual an abbreviation for or the approval of Acorn for use with it are All information of its use manual are given by owledged that there of details of any this manual can be obtained upon request Acorn Computers welcom comments and suggestions relating to the product and this
39. anual 2 Packaging and installation The microcomputer is supplied with three part moulded polystyrene packing in a cardboard box Supplied with the microcomputer is a Welcome Guide an aerial lead a welcome tape a welcome disc two reversible keyboard inserts a VIEW reference card a ViewSheet E reference card and a guarantee card The mains supply for UK models is 240V AC 50Hz The microcomputer is supplied with a moulded 13 amp square pin plug If this plug is unsuitable then it must be cut off and thrown away Instructions for fitting a replacement plug are given right at the front of this manual The microcomputer is turned on by a switch at the back of the microcomputer next to the mains lead Do not use the microcomputer in conditions of extreme heat cold humidity or dust or in places subject to vibration Do not block ventilation under or behind the computer Ensure that no foreign objects are inserted through any openings in the microcomputer 5 Issue 1 Master Series Service Manual 3 Disassembly and assembly To service the BBC Master Series Microcomputer first disconnect the power supply plug from the mains and remove all peripheral connections from the computer To disassemble The lid of the microcomputer case may be removed after undoing the four fixing screws underneath the case DO NOT remove the lid with the mains power co
40. anything in the configuration syst For example puter were configured to power up with a ther than a hard disc th tem that would cause is would happen if the floppy disc drive as therefore making the hard disc seem the User Port left trailing across a carpet the the 2 Ensure that the software has not selected the internal pages amp FC and amp FD 3 As with any straightforward parallel data bus any faults with this have to be found by methodical checking of all connections a Ensure the remot quipment is not at fault if possible b Ensure the cables and connectors are in good condition and are correctly assembled i e cable clamps are fitted and effective c Ensure that any non polarised connectors are correctly inserted d Cables longer than 1m should in general not be used e Check that each and every connection is correct as per the circuit diagram f Check that the READY signal from the 10 Controller IC15 pin 17 goes to both the CPU IC14 pin 2 and the Peripheral Bus Controller IC21 pin 11 g Check that the FIT connection from the 10 controller IC15 pin 38 goes to the PBC IC21 pin 5 h Check that all address connections to the Memory Controller IC20 are correct i Check that the two data bus connections to the IO Controlle
41. ard This board has two connectors a A 5 way connector which has a one to one connection with the DIN connector b A 15 way connector provides the CPU data bus together with address timing reference chip select and interrupt signals The main pcb has two further address connections for future expansion External Second Processor This interface has a buffered data bus via the Peripheral Bus Controller PBC The EXbus on this component provides for good data set up and hold times Together with a limited degree of line matching this ensures reliable high speed data transfer with unspecified cable lengths A maximum cable length of one metre is suggested to prevent noise problems Th interfac operates at 2Mhz This means that if a 1Mhz bus peripheral is also connected then the address and data buses on this connector will appear to perform both 1 and 2MHz cycles The connections are DO to D7 Data Bus CMOS levels AO to A7 Address Bus TTL levels IRQ Interrupt Request Open collector TTL levels nTUBE Parasite chip select TTL levels Supply 5V Ground OV 27 Issue 1 Master Series Service Manual 6 Test equipment A PORT tester is available for the microcomputer It will check the DRAMs including siueways RAM CMOS RAM and all the 1 0 ports on the microcomputer disc printer user 1MHz bus TUBE UHF video ROB RS423 casse
42. ata formatting error checking that is neccessary for both systems It is fully described in the March 1983 edition of the Hitachi Microcomputer Databook SERPROC The ACORN proprietary part the SERPROC is effectively a multiplexer and baud rate generator for the 6850 It also generates the phase continuous transmission circuitry for use with the cassette interface Buffer Components The RS423 transmit data and CTS lines are buffered by an AM26LS30 or equivalent This provides a single ended transmission with slew rate limited output RS423 receive data and RTS is buffered by a uA9637AC or equivalent Both buffers are connected with single ended input configurations 26 Issue 1 Master Series Service Manual Cassette data output from the SERPROC is buffered by a single non inverting operational amplifier with a simple single pole filter a c coupling capacitor and current limiting output resistor 2MHz External 1 0 Two peripheral devices operate at 2MHz These are th xternal second processor connection and the ECONET connection ECONET Module Connection is made to the ECONET by a five way DIN connector mounted on the main circuit board The interfac lectronics including the 681354 line drivers receivers and chatter disconnect components are mounted on a separate circuit bo
43. cured should still be replaced Their long term reliablility may well be impaired 3 Check the 16MHz oscillator output IC43 pin 2 and check that it is reaching the VIDPROC IC42 pin 8 The signal should be reasonably clean 4V peak to peak If not then check the crystal controlled oscillator circuit Warning if the system 16MHz c lines could be held low permanent damage If the os not reaching the VIDPROC quickly as possible Do not than 30 seconds at a time 4 Check the 1 2 4 and 8 MH ormed by h Th el er alf of IC43 and X2 lock does not work the DRAM RAS and CAS is can make the ICs heat up causing llator is not working or the clock is y to find the fault and repair it as leave the computer switched on for more Signals from the VIDPROC IC42 pins 4 5 6 and 7 respectively If any is missing or is not a clean square wave with MI logic levels then replace the VIDPROC 1C42 5 Check that there is a clean 2 MHz signal on the CPU clock input shorting track 1C14 pin 37 If it is missing or incorrect then check for broken or 6 Check that all data and address bus lines are clear of shorts between themselves 5V and ground 32 Issue 1 Master Series Service Manual 7 Check that the system ROM is plugged in 8 Check the RAS and CAS signals to the main DRAMs ICs 17 and
44. e 1 Master Series BBC Master Series Microcomputer Service Manual Contents 1 Introduction 2 Packaging and installation 3 Disassembly and assembly 4 Selection links Hardware description Introduction Core machine Internal 1 0 External 1 0 N PR Test equipment Fault finding Switch on Sideways RAM Video Real time clock Analogue port RS423 port Cassette interfac Disc drive interface Parallel printer port 10 User port 11 1MHz bus 12 The Tube 13 Internal co processor 14 Sound output 15 Modem connector 16 Cartridge port 17 Econet 1 O O1 I o OY O1 01 O1 O1 a Appendix Connector pinouts Parts list Component locations PCB circuit diagram Final assembly EPROM cartridge circuit diagram Econet module circuit diagram Keyboard circuit diagram Service Manual Issue 1 Master Series Service Manual 1 Introduction This manual is intended to provide the information required to diagnose and repair faults on the BBC Master Series Microcomputer which was designed by Acorn Computers Ltd of Cambridge England The information contained in this manual is aimed at servic ngineers and Acorn dealers who will be servicing the BBC Master Series Microcomputer on behalf of Acorn Computers Ltd 4 Issue 1 Master Series Service M
45. es are broken up Check all connections to the PBC 7 4 Real time clock 7 4 1 Gives strange characters 1 Type in the correct time and try again nent 1 Check that the variable capacitor VCI is 32 768 KHz is at 1C11 pin 2 If it is not oscillator circuit X1 VC1 C6 C7 R17 and R24 2 Are all 3 Are al correctly See 7 1 9 connections to the system VIA corre in the circuit check all the values in the ct Check that the components in the chip select power down circuit fitted 7 4 3 Loses a lot of time 1 Is the battery connector PL8 securely fitted with all three pins engaged Are the battery leads properly soldered to the battery clips 2 Is the battery flat If it is then replace it in its holder next to the speaker inside the computer being careful to insert the new battery with the same polarity as the old one 3 Is there at least 2 6V at the clock chip with mains power switched off If not the battery may still be flat but check the FET Q4 and surrounding components first 40 Issue 1 Master Series Service Manual 7 5 Analogue port 7 5 1 Gives completely erroneous results on all channels 1 Are all the connections on the external plug correct E 2 Has it got an incorrect or faulty integration capacitor C49 3 Check that the reference voltage is approximately
46. escription 5 1 Introduction ic The Master Series Microcomputer consists of a central processing unit with associated memory and various input output devices for communication with external equipment Only a fully configured system will be described here although reference to sub systems will be made where relevant The Core Machine All input output 1 0 computing is performed by a 65C12 CPU with its principal ancillary components 128 Kbyte of Dynamic Random Access memory Special expansion options allow a further expansion of 64 Kbyte Dedicated hardware can be used to expand this almost indefinitely 262 Kbyte of Read Only Memory Special expansion options allow a further expansion of approximately 1 2 Mbyte of ROM Plug in cartridges are available which accept up to 256 Kbyte of ROM Internal 1 0 Various 1 0 devices operate solely within the confines of the system to either improve facilities or increase throughput These are as follows 6522 VIA devices Two of these are provided and interface to 1 A 93 contact keyboard with 2 key rollover 3 Channel sound generator with additional noise channel Battery backed up Real Time Clock and fifty bytes of RAM 2 The Printer Port and User Port Co processors These consist of an additional CPU with associated memory They have no I O capability of their own and depend entirely
47. etect present present 12 Plug t present made B East Two positio n link Link between C and D The cartridges are clocked by This is a synchronous signal with to the cartridges East Video Two position link this case a clock source MUST be provided or the dynamic memories the 8 MHz signal the 2 MHz phi2 Note that the link between A B signals is determined by this link It a track on the bottom of the PCB causing true polarity be broken and a piece of wire used to make the link LK10 fitted for NTSC only Channel Select the modulator enables one of two to be selected Note that the computer as supplied for use in fitted with a UHF modulator so LK10 is not fitted CSYNC Cartridge Machine Position A This connection to the computer CSYNC line is provided E Position Master con B they are plugged into a Master Series computer or an Acorn ters are shipped with to appear on pin A10 of the cartidges npu a logic LOW or GENLOCK purposes Certain hardware cartridges may need to detect whether connection to this pin this link in the Electron B position causing The Electron has no Issue 1 Master Series LK13 PCB track made West Two position link As 8 A to If t betw If t prec hipped D conv rter refer he 1K13 een ana
48. fitted by the user the warranty may be invalidated a The keyboard mounted battery is charged whilst the computer is running from the mains supply The proportion of charge accummulated during operation is shown in figure 6 for an initially flat battery This is an approximation dependent on conditions of use as the actual charge accumulated will vary with temperature and duty cycle i e ratio of time on charge to time on discharge i 1 100 i 1 90 i i z 80 j 70 P t 60 i typical 5 l charge aiu S A AA RI Ar ATE TE accumulated gt H 10 1 bar a amp 5 0 1 2 100 120 140 160 180 Time switched on hours Figure 6 An over charge prevention circuit is provided with the following action a Upon switch on charging current of about 30mA is applied b After approximately 15 minutes the charging current falls to c Trickle charging continues at 1mA for as long as mains power is applied The minimum charge burst is designed to provide battery back up over a weekend after just a few minutes operation 21 Issue 1 Master Series A 10uf capaci connections accidental ba Configuration he chip Twe or initial is con Service Manual tor is connected across the clock chip supply This is to prevent loss of data in t
49. h is driven active low when a row column combination describes a depressed key RO to R7 The keyboard row input connections are normally held high by internal pull up resistors If a key is depressed it will cause the appropriate row connection to be pulled low when its column is selected CO to C14 Thes open collector column driving outputs are sequentially taken active low in auto scan mode at a rate of 1MHz In polled mode nKBEN active low the slow bus inputs PAO to 3 determine which output will be low The selected column output is a direct decode of these inputs CA2 Connected to the system VIA this output will cause the VIA to generate an nIRQ The line will be active low when an active key is detected 19 Issue 1 Master Series nKBEN Generated by the system VIA System TT sed zl This is the tin unction keys The matrix is as foll S u The keys are physical f LOWS ning reference Service Manual this line is taken active low to RSTO These connections are not The Keyboard Matrix ly arranged as a 4 cursor control keys and a 19 key numeric ERTY type keyboard co C1 C2 C3 Ch C5 C6 C7 c8 C9 C10 RO R1 TAB Z sp Y B R2 SHIFT S C G H LOCK R3 CAPS A X F Y LOCK 1 amp R4 1 2 D R 6 R5 W E T 7 EX R6 Q 3 4 5 f R7 SHIFT CTRL Figure 5 Sound Generator The sou
50. he event of tery disconnection Status Fifty bytes of CMOS RAM are available within ty of these are used by the operating and filing systems n reserved for figuration of the hardware Of the remainder ten ar future use by ACORN ten are for Third Party use and the remainder are for the user Clock trimmi clock output The provided with automatic leap year An correction system alarm ng capacitor clock operates from a 32 768KH crystal oscillator A is provided as is a test point with the buffered month day hour minute and second information is but not automatic leap century included within the chip but operating Year alarm is also support to this facility is not provided An optional nIRQ connection can be made to the CPU from the clock chip enabling the to change program flow Operation of the clock chip in this manner involves direct manipulation of the ch should only be attempted by competent programmers responsible not control signals and Acorn Computers are the user software ip for incorrect programming by supplier wri If power is removed during an access to this chip will become invalid the chip select the possibility o E This cannot however remov access sel ect with a transistor whose collector resistor s being corrupted This is done by i
51. ised when the A D control register is so instructed Conversions are in the range 0 to 1 8V The voltage reference is made available at the connector Provision is made on the board for an additional high stability reference if required A link will have to be made for the additionl reference to be used Conversions take place in 5mS and the end of conversion pulse causes an IRQ to be generated by the system VIA Auxiliary Connections Two fire buttons are provided for with the connections 10 These are connected to the system VIA and cause interrupts as IRQ to be generated A light pen may be connected to the signal LPSTB This also causes the system VIA to generate an IRQ if enabled It also causes the 6845 CRTC to latch the address of the currently selected video data byte This may not be the same as the displayed byte and some software correction may be necessary Factors such as phosphor characteristics light pen response and the angle at which the pen is used may all affect the correction needed Serial Ports Cassette and RS423 Much circuitry used to provide the RS423 port also generates cassette interface signals For this reason these will be described together with the differences where appropriate E U A R T The device responsible for providing most of the serial port functions is the 6850 UART This has all the receive transmit and d
52. it may be mains s could happen in places with poor 3 On some early computers pin 15 should now be connected to 5V 7 15 Modem connector of IC10 was connected to PRST It 1 Check the controlling software VERY carefully 2 Check all connections to the connector 3 Check that a signal arriving at the connector goes through it i e there are no dry joints or faulty connector sockets 48 Issue 1 Master Series es 7 16 1 Causes the sound output to be noisy 1 2 po 3 wo 4 Are all con ea 16 Cartridge port Service Manual Check the cartridge for shorts and general layout Are all the links assoccia sition rn through ch other 5 Are any of nnector must be replaced co 7 17 RBeonet Ec wi However ther Is the cartridge for the Is the cartridge edge connect Appendix ar the test equipment Follow the 16 2 Will not recognise some cartridges Electron Not all of these are compatible ted with the cartridge in the correct tor excessively worn e g gold plating nections to the edge connectors correct without shorts to the edge connector blades bent or worn If so the onet can only be serviced properly by Econet service centres who 11 have the necessary test equipment to check the system thoroughly a few simple things which can be checked without Econet board circuit diagram in
53. k line IC14 pin 4 is not stuck low or high The 1C20 and CMOS clock RAM 1C11 both have d the system VIA second If this interrupt IRQ li ne will appear to be stuck low This data line to the VIA i r inst 8 alled software aulty 7 1 8 Not all keys work on the keyboard One of two possible keyboard circuits may be fitted a A 40 pin keyboard encoder way connectors 1 TH 2 TF more more than one key is the keyboard encoder 1 FF IC16 a row or column one key on yisa ected check for a faulty connectio to the keyboard than one key is middle of a row or col umn EE ec in the 3 Tr 4 TES Note is immediately connect one key onl y is a EE ected check for a broken track in of the keyboard matrix ted check for a broken track at the e keyboard matrix the beginning of ted then check the keyswitch itself a row or column is the end of a PCB track ted to the encoder circuitry The end column is the other end of the PCB track Because of the beginning and end of a track are not necessarily track which are visually nearer or farther from the encoder circ irect IRQ line The latter part has a link LK4 which can from IRO C8 generates an interrupt every 100th of a i
54. ly one of them has line termination resistors in 7 8 5 Data can be read but it is wrong or you get Bad FS map in ADFS 1 Try the disc drive in another computer If the fault persists then the disc drive is at fault 2 Issue 1 boards only There should be a small capacitor from the DRQ line to ground Is this fitted Is its value correct 3 There may be a fault in the memory system Check that the address inputs to the Memory Controller IC20 pins 21 to 28 inclusive are switching with good logic levels Check that the outputs the AA and AT lines are switching A good test here is to press BREAK repeatedly and look at each line in turn 4 Check tha address mult 1629 and 5 Use a memory test program to validate memory necessary as the memory chips are highly reliable 7 8 6 Data can be read correcty but 1 Is the disc versa The bui tiplexers t the AA and AT lines are correctly co EC33 format lt 4 in ted for DFS but cannot be written reliabl This is rarel nnected to the y being used with ADFS or vice ormatter is only for use with DFS 2 Check the disc drive on another computer if possible 3 Check that data pins IC3 pins 22 and 21 1770 IC3 and the 74LS174 4 Follow the signal path of Note a di sc drive must be outpu VD to the connec
55. memory will be displayed When bit E in ACCCON is set if the address range is amp 3000 to amp 7FFF the CPU will read write Lynne according to the flow shown in figure 2 15 Issue 1 M no ee a A This system allows for the screen bit m OT only CPU memory map will however H 1 R NON Wait until end of CPU clock cycle Was the X last cycle an V opcode fetch SYNC 1 From amp C000 to I amp DFFF in RAM Rm eee eee Is this cycle an opcode fetch MS Read Write Lynne 1 1 Ao ap to be which it t occupies work if the screen from a known region provided to permit the MOS VDU drivers screen access 1 0 illegal Bit X in ACCCON re directed to LYNNI hence considerabl when set causes all E This occurs irrespective o car will cleared the memory In the same way value amp 8000 when that the LYNNE M gt a significant proportion is being accessed by opcodes accesses to region have to be exercised nn nn nn mm meme removed from the main T A mechanism is also a to be the opcode address in its use When Pa map returns to its usual C variable HIMEM BAS format
56. nd generator is an SN7694A device N ESC f1 f2 f3 f5 f6 f8 f9 gt 2 e y copy E 3 0 P 9 0 _ t7 t one pseudo random noise channel are provided it is found in the manufacturers dat reference clock of 4MHz from central described in the section ta sheet del It 8 C11 5 1 enable the row and column addresses to be determined by the Operating with 10 keypad C12 2 del ret Three sound channels plus The full description of is provided with a timing The output is filtered as Audio Circuitry The output can also be connected by screened cable to the optional modem This output is mixed on tones for DTMF exchanges wher such tones itself 20 the modem board to generate dialling the modem hardware does not provide Issue 1 Master Series Service Manual Real time clock with RAN Battery back up A 146818 RTC and RAM chip is provided with battery backed supply The chip operation is described in the manufacturers data sheet In its fully charged state the internal lithium manganese dioxide battery will provide over one year of back up power Alternatively components may be fitted to the circuit board which provide for the fitting of a rechargeable battery on the keyboard This battery like its support components are not fitted as standard If these are
57. nent operates at this the internal second processor TUBE Its data bus is connected directly to the CPU data bus X The second processor interface will only be specified as a hardware data transfer de inition In this way the actual second processor used will not be constrained by this specification This is a parallel port providing the following data access signals i DO The foll to D7 A bi directional bus to TTL levels ii AO to A2 A uni directional bus to CMOS levels lowing control and timing signals are provided Host CPU phi2 CMOS levels System Reset 2 TTL levels Host CPU nIRQ This must be an open collector node with an active low TTL level 8MHz timing reference TTL levels TUBE chip select CMOS levels Read Write TTL levels 23 Issue 1 Master Series Service Manual 5 4 External 1 0 1MHz External I O Screen Output There are two chips primarily responsible for providing the screen output a 6845 b Acorn proprietary VIDPROC 1C42 High Resolution Modes The 6845 generates a linear memory address sequence which increments every 0 5 us or lus depending on the video bandwidth selected and video data format The amount of memory reserved for screen use is also varied The E available options are shown in figure 7 Vide
58. nnected Inside the microcomputer are four main sub assemblies keyboard speaker and battery unit the cartridge nest power supply unit main printed circuit board To remove the keyboard first unplug the 2 keyboard connectors from he main printed circuit board Undo the 3 screws holding the keyboard o the case bottom and the 1 screw which holds it to the power supply nit ct c To remove the speaker and battery unit simply lift the casing upwards and then unplug the two connectors joining it to the board The power supply unit is connected to the main circuit board by seven push on connectors which must be unplugged Three screws on the underside of the case are undone allowing the unit to be removed On reassembly ensure that the same type of screw is used M3x6mm The main printed circuit board is removed complete with the metal back plate To remove the main printed circuit board undo the 4 fixing screws which pass through the cartridge connectors into the case bottom and the 1 screw which holds the metal back plate to the power supply unit Remove the circuit board from the case by lifting it slightly at the rear and then sliding it backwards To reassemble Replace the main printed circuit board by putting the front edge with connector headers in first and pulling it forwards until the metal back plate drops in Make sure that all the lugs on the lower case
59. nverting the chip is connected to the battery backed supply As power fails to the main circuitry the transistor base current reduces and the transistor switches off deselecting the chip 1 MHz Internal 10 Various devices operate at a 1MHz bus rate Only one internal I O component works at this speed the system VIA 22 Issue 1 Master Series System V interrupts an om Port B on hardware si Service Manual A A 6522 allows several sources to create maskable The sources are CRTC vertical synchronisation A D converter end of conversion signal CRTC light pen strobe Keyboard key detect It also provides the previously mentioned slow data bus this device generates and reads a number of internal trobes These are as follows Port B Data Strobe Active Level Port B D7 DXXX XDXX XXDX XXXD X XXX XXXX XXXX XXXX XXXX XXXX XXXX Data Strobe Active Level DO XXXX Clock Address H XXXX Clock chip enable H XXXX Fire button 1 Input XXXX Fire button 2 Input DOOO Sound chip select L DOO1 Clock R W E D010 Clock Data Q D011 Keyboard enable Q D100 CO Screen control L D101 C1 Signals H D110 Caps Lock indicator L D111 Shift Lock indicator L Note Q is the value of D after the port write operation is completed 2MHz In ternal Speed I 0 Only one internal I O compo
60. o Data Formats Mode Format Reserved Memory Pixels Byte Bytes 0 8 20K 1 4 20K 2 2 20K 3 8 16K 4 8 10K 5 4 10K 6 8 8K 7 Teletext 1K 128 8 20K Y 129 4 20K 130 2 20K Reserved 131 8 20K gt in 132 8 20K LYNNE 133 4 20K 134 8 20K 135 Teletext 20K Figure 7 All modes except 7 and 135 display a bit mapped image of the reserved memory The 6845 may be re programmed to display any arbitrary section of memory If this is done however the hardware scrolling will not work correctly as it assumes that the screen memory is in its usual location The screen always ends at amp 7FFF and starts 1 8 10 or 20K further down than that depending on the selected mode The selection of video bandwidth and data format is performed by programming the VIDPROC The cursor size and position is also controllable by VIDPROC Special measures have been taken to ensure correct cursor operation in the Teletext modes 24 Issue 1 Master Series Service Manual Teletext The Teletext modes do not generate a bit mapped display but a character cell one The character graphics ROM within a SAA5050 device generates RGB signals according to the desired character graphics information within the reserved memory space Each byte of memory is therefore just a definition of the character graphics symbol required Other SAA505X devices may be used when different languages are
61. o the ap between the original start of screen and scrolled start of screen hen this is done only the end of screen needs to be written over in AM If this is not done th ntire screen appears to roll over he amount of modification to be used is controlled by two nodes CO nd Cl D H D Q Video Output Three outputs are provided for displaying video data These are a PAL NTSC encoded UHF carrier On channel 36 with 1 5mV into 75 ohm b Composite video This is a iv peak to peak signal c Digital Red Green Blue outputs These are approximately 75 ohm outputs For use with NTSC the modulator has to be changed from UM1233 E36 to a VHF equivalent Provision is made for selection of either one of two channels with V H F A Molex type link has to be inserted for this 25 Issue 1 Master Series Service Manual Analogue Port This 15 way D type connector provides access to an NEC uPD7002 4 channel 10 bit analogue to digital converter The sampled input is compared to a 1 8V reference derived from three small signal diodes in series A tracked link may be cut to deselect this reference The user may then solder in a two pin precision reference in the holes provided or supply an external reference Any user supplied reference should have a maximum voltage of 2 5V Conversion An input voltage on any one of the 4 channels wil be digit
62. of that colour as the coloured insert in the base of the plug Different manufacturers plugs and fuse carriers are not interchangeable In the event of loss of the fuse carrier the moulded plug MUST NOT be used Either replace the moulded plug with another conventional plug wired as detailed below or obtain a replacement fuse carrier from an authorised Acorn dealer In the event of the fuse blowing it should be replaced after clearing any faults with a 3 amp fuse that is ASTA approved to BS1362 If the socket outlet available is not suitable for the plug supplied the plug should be cut off and the appropriate plug fitted and wired as previously noted The moulded plug which was cut off must be disposed of as it would be a potential shock hazard if it were to be plugged in with the cut off end of the mains cord exposed As the colours of the wires may not correspond with the coloured markings identifying the terminals in your plug proceed as follows The wire which is coloured green and yellow must be connected to the terminal in the plug which is marked by the letter E or by the safety earth symbol I or coloured either green or green and yellow The wire which is coloured blue must be connected to the terminal which is marked with the letter N or coloured black The wire which is coloured brown must be connected to the terminal which is marked with the letter L or coloured red 2 Issu
63. orts As a last resort try changing chips 2 Check resistors R69 75 77 78 84 85 87 89 90 for the correct values and that they have good signal levels at their IC40 ends 7 3 5 The screen displays the wrong colours 1 Check 1 and 2 above 39 Issue 1 Master Series 7 3 6 The display works in These modes work very dif There are a number of faul erently from the others Lts which only exhibit themselves in these Service Manual all modes except 7 and 135 using the SAA5050 modes 1 There is a cursor which can be moved but no text Check the 6MHz input to the SAA5050 It will have a slightly variable duty cycle certainly not 50 but no part of the waveform should be narrower than about 40ns If so check all components and signals around the 6MHz generator IC39 and 1C25 2 The text is at all fragmented Check as above 3 Not all colours are present Check all connections to the VIDPROC 1C42 Are the pull up resistors R51 R54 and R56 present and the correct values 4 Not all characters can be obtained Check all data bus connections the the PBC IC21 pins 21 to 28 5 Lines of normal size text appear cut in half Check VSYNC at the CRTC IC22 pin 40 6 Rounded characters appear unstable Check the components and signals around the 6MHz generator 1C39 and 1C25 7 7 4 2 Does not incren T Zlin Lin
64. ower supplies which will short circuit if any two are Replace the lid and insert and tighten the four fixing screws i Issue 1 Master Series 4 Selection links LK1 PCB track made A 1MHz 2 position link In the A position the 1MHz Bus Bus Audio signal audio mixer In the B position the 1MHz Bus signal audio circuit Minimum load 1k This link is a permanent track cut before a wire link is used LK2 PCB track made decoupler Cartridge One position link In some instances particular car ohm in the A position to make the 25M to be fitted and LK2 which cut LK3 Not present LK4 plug made One position link The alarm is the shunt from is a Clock chip IRQ Service Manual Input Output is an input to the computer s is an output from the computer s The track must be B position tridge hardware may need a 5V supply that is decoupled from the main computer 5V load To do this R9 needs track on the circuit board should be 6818 clock RAM chip has a daily alarm function built in When the triggered the CPU is interrupted via its LK4 disconnects the CPU IRQ line Removing IRO line to the clock line This function is not supported by the operating system as this feature may not be present in Consequently the clock application software
65. r are correct IC15 pins 18 and 19 7 12 The Tube 1 Check 3 a b d e f g h and i as for 1MHz bus above 7 13 Internal co processor 7 13 1 Not being recognised 1 Is the configuration status correct 2 Are the two connectors correctly mated 47 Issue 1 Master Series 3 Are two bits of the data bus correctly connected to the I0 Controller IC15 pins 18 and 19 Service Manual 4 Are all connections to the two connectors correct 7 13 2 Recognised but just a cursor in the top left hand corner of the screen 1 Is the co processor working Try 2 Are the two connectors correctly 3 Are the boot ROM s correctly in it in another computer mated serted in the co processor 7 14 Sound output 7 14 1 Will not work at all 1 Is the speaker connected 2 Is there an external speaker to the sound phono connector at the rear of the machine which is short circuited or of very low impedance less than 4 ohms If so remove it 7 14 2 Will not work with all envelopes 1 Has your software requested too many channels Th nvelopes us memory shared with serial data buffer space 7 14 3 Produces strange sounds whenever a key is pressed 1 Are all the connections to the circuit diagram 2 Try pressing BREAK f the sou noise affecting the computer Thi mains supplies sound chip correct as shown in the nd goes away then
66. s before starting afterwards les and 300ns Remember to put them back 3 Use sharp pointed meter probes to push through solder resist This will make finding short open circuits 4 Always suspect connectors Ed 5 If you find a recurrent fault e g know at ACORN so that we can include more reliable more than 10 machines let us it in this manual if appropriate 29 Issue 1 Master Series Service Manual The following items of test equipment are required for fault finding A set of screwdrivers Pliers Cutters 10A Multimeter RGB monitor logic probe 5 ohm 5W resistor u The repair will be quicker with 100MHz dual beam oscilloscope Good quality scope probes TV composite monitor colour monitor cassette player disc drive PORT tester frequency counter A known good computer to use as a signal model 30 Issue 1 Master Series Service Manual Note the Peripheral Bus Controller IC21 is used to buffer the data bus around the system It also isolates may parts of the system from each other to help improve reliability It may disguise data bus failures or open circuits Be sure not to assume that any node is connected to any other unless you have checked it This particularly applies to the SAA5050 and all 1MHz operating components E g the User VIA going down could stop the System
67. s exist connected via a separate data bus The four the least significant bit of ROMSEL selects between is active from C000 to amp FFFF within a 128 Kbyte ROM four 32 Kbyte ROMs where the upper and together with a ROM which This ROM is 32 Kbyte devices and one 16 Kbyte device are connected in a matrixing scheme as shown in figure 3 Segments 8 7 6 5 4 Chip Selects or RAM enabling 1 i 1 1 L Output la ddr i Enable i 1 1 1 Cartridge ROMs Chip Select y o Segments 3 2 1 0 Output enables Figure 3 17 Issue 1 Master Series Service Manual In this way fewer connections to the controller logic are required to select agiven ROM although the power dissipation will be increased 1f all the ROMs in one column are inserted A chip select will be driven low if an access to one of the segments 4 to 8 is required If a cartridge ROM is required then the Cartridge ROM chip select will be driven high All chip selects are a decode of the CPU address most significant nibble An output enable is turned active low during the CPU phi2 period depending on which segment is required The segment to be selected is determined by the binary number held within the least significant nibble of ROMSEL Overlaid RAM in ROM area When the bit RAM is set in ROMSEL accesses to the
68. s not cleared by the operating system each could is faulty or if an address or IC16 on the main circuit board and two 15 possibly with an intermediate buffer board joined to the keyboard with ribbon cables n from the nd of which of a row or layout the the parts of the uitry 33 Issue 1 Master Series Service Manual b A 17 way connector rising to a keyboard with the encoder circuitry on Et 1 All of 1 to 4 in the previous section 2 Check for a faulty connection from the main board to the keyboard which may cause th ntire keyboard to be affected 7 1 9 All the keys are working but CTRL BREAK behaves as BREAK CTRL BREAK should invoke the configuration settings 1 Check that all power down components around the CMOS clock RAM chip 10611 are present and have the correct value On some early computers Cll needs to be 100uF instead of 10uF D8 should be changed to IN4001 and 03 should have a 1k8 resistor between its base and emitter 2 Check that the chip enable pin 13 of IC11 is normally high with Just occasional excursions low If not then check the system VIA IC8 for the RTC chip select pulses which should be on pin 16 3 Real time clock chip control lines should be in the following state at all times when not being accessed by the user CE IC11 pin 13 high
69. signal does n is probably a short in h HSYNC latter the video outputs check that all tors the resis are correct Service Manual three different types of monitor should be B and composite IC25 where it ot make good logic levels that area period 64us A way of getting the EXOR gate output tor tors in going into them 3 If it only occurs on UHF resistor network 1C40 pins 12 to 75 77 78 84 85 87 and 89 4 If it only occurs on RGB check al the connector 7 3 2 The display is correct vert Do they all diagonal lines Does it occur on RGB 1 If so 2 Then follow the signal is combined with VSYNC then ther at any node Note iz former when HSYNC appear measurement of HSYNC period period to have 64us is glitches tical ly check HSYNC is correct on the CRTC This 38 UHF and Composite video 1622 pin through the exclusive OR gates If the signal does not make good logic levels is probably a short in that area EXORed with VSYNC former will have the latter superimposed upon it should be have good signals check the signal as it passes through the 19 inclusive through resistors R69 the signals going to the back of but is broken into moving IC25 where it period 20ms This will make the ignored the
70. ssue 1 Master Series Component Locations tables transis circul The following diodes and Appendix The show the positions of ICs Service Manual resistors capacitors tors on the circuit diagram given later in the t diagram is split into 2 sheets which the component appears is given in the Sheet column the x y coordinate of each component by 10 grid drawn on each sheet column gives and the sheet on The Position with respect to a 10 of the circuit diagram 62 Issue 1 Master Series Service Manual IC nos Location Sheet 1 1 8 1 9 2 2 2557144 2 3 2 8 2 4 2 2 5 2 6 2 6 2494 2 50 2 7 2 2 2 8 2 8 2 9 4 2 5 4 5 5 6 5 2 10 4 8 2 11 6 7 2 12 6 6 2 13 4 3 2 14 2 8 1 15 2 6 1 16 6 3 2 17 6 0 1 18 4 0 1 19 9 4 3 5 6 6 0 8 0 9 1 20 35 9 1 21 9 3 9 4 1 22 Jd 2 23 5540 1 24 3 8 4 8 1 25 6 5 7 9 1 26 3720 1 27 4 8 1 28 2 5 6 1 29 Tu 1 3o 4 5 1 31 4 4 1 32 155 3 1 33 4 6 1 34 2 1 6 2 7 9 1 35 9 5 9 6 1 36 2 0 2 1 3 1 1 37 5 8 1 38 5 1 5 7 6 7 1 39 5 5 0 8 1 8 0 9 1 9 1 40 po 1 41 6 8 1 42 6 3 6 4 1 43 8 5 8 6 1 44 45 dd 43589 2 46 8 6 7 6 8 7 2 47 48 7 8 2 49 79 2 50 8 8 2 51 B 2 63 Issue 1 Service Manual Location Sheet Master Series R nos NN CV CN CV CN CN NT N N N N NN CN CN CN CN CN CN CN CN CV CN CV CN CV CI CN CV c CN NN CN N NNN
71. t the test the 5V R11 5 2 9 appears on the outputs of the 7415244 buffer 109 7 Check that a strobe pulse appears on IC6 pin 39 for every character the User VIA 8 Check that a strobe pulse is found inverted at pin 11 o 102 and true at pin 8 of the 7438 IC2 7 10 User port transmitted If not then check all address data and control pins on f the 7438 1 Is the software illegal for example using peek and poke type commands from a second or co processor If so this is the problem It would work on the I O processor alone but this is not recommended E the cause of 2 Is the shift register being used to transfer data on the CA lines There is a fault in some manufacturers 6522 s and for th is reason the use of this feature of the 6522 is not specified for the computer 3 Check the software very carefully 4 Check all address data and control lines to the User VI 46 A 106 Issue 1 Master Ser 5 Have vol pins If s Note this and the ot 1MH Is 1MHz com bus ies tages outside o the VIA may could arise i her end is bus to b deselected default ral not to wor for instance a Cable is left connected th Service Manual the supply range been applied to any of the have been damaged there
72. t the lines CO and Cl from the 7415259 IC10 pins 4 and 5 to the CRTC Multiplexer 1631 pins 38 and 39 are properly connected and change at 4 Check that with no short 7 2 Sideways 1 Check all c 2 Check RAS a 3 Check that for your use least once if you switch between modes the lines from the CRTC MUX or open circuits IC31 to the DRAMs are correct RAM onnections to the memory address multiplexers nd CAS at the DRAMs see figure 8 the two links LK18 and LK19 are in the correct position 37 Issue 1 Master Series 7 3 Video To debug the video TV ROI connected all 7 3 1 The display scrolls vertically round the Screen video 1 If so 2 Then follow Does it occur on RGB the signal is combined with HSYNC at any node then ther Note when VSYNC period former will round the CRTC IC22 pin 40 and then Does it only occur on one of 1 Is the CSYNC polarity link 2 If it only occurs on composite video to the output transis R147 to RI 50 20ms is xamin check VSYNC is correct on the CRTC EXORed wit be difficult to spot within the this is to synchronise the oscilloscope from the VYSNC output of th inclusive accordance with the circuit diagram LK5 correct for your moni UHF and Composite IC22 pin 40 through the exclusive OR gates If the
73. tor connected at this resistors for the line driver outputs are within the disc drive 45 stage t should be normally high with low going transitions as transitions are appearing on the 1770 WD and WG If not then check all connections to the 168 pull up The Issue 1 Master Series S 5 Follow the signal path of WG to the connector Note a disc drive must be connected at this stage ervice Manual as pull up resistors for the line driver outputs are within the disc drive The output should be normally high with low going transitions 7 8 7 Data can be read and written correctly but only on can be selected out of two 1 Check all connections to the 74LS174 IC4 e disc drive from the 2 Check that only one drive select output is a logic LOW 7438 IC2 pins 3 and 6 7 9 Parallel printer port 1 Check that the configuration system is set up correctly CONFIGURE PRINT 1 Use the default printer driver to co tests If the fault only shows up with a custom printer driver ftware carefully first 80 3 Check the printer with another computer if possible 4 Check the computer with another printer if possible 5 Check that pin 40 on the User VIA 1C6 has a pull up t but is not short circuited to 5V 6 Check that data appearing on Port of the VIA IC6 pin i e nduc
74. tte A to D and sound output To use this tester the microcomputer must at least have the CPU running and the MOS BASIC ROM working and some of the RAM working The PORT test software is contained in a cartridge ROM and on disc Full operating instructions are supplied with the equipment 28 Issue 1 Master Series 7 Fault finding This section goes step by step throu diagram and component location tables TE any part of the machine is suspect ct no loose connectors and broken cabl 2 no broken or shorting tracks 3 ICs plugged into their sockets corr points should always be checked first Service Manual gh fault finding in each section in the Appendix ed of being faulty es ectly of hardware It should be studied in conjunction with the circuit the following 4 power supply working and reaching the components concerned 5 all digital signals are either at c than 2 4V for 1 less than 5V for 0 greater than 3V for 1 less than 1V f be true for the period 150ns before phi2 on read cyc lean TTL logic levels greater or clean CMOS logic levels or 0 On timed signals this must before phi2 on write cycles Hints for repair 1 Never solder to a computer which is switched on 2 Remove all user ROM
75. ual The current memory map is dictated by the contents of the two latches ROM SELect and ACCess CONtrol located at amp FE30 and amp FE34 respectively The contents of these two latches are as follows d7 d6 d5 d4 d3 d2 dl do amp FE30 RAM 0 0 0 PM3 PM2 PM1 PMO amp FE34 IRR TST IFJ ITU Y X E D The contents of ROMSEL dictate the selection of memory which resides from amp 8000 to amp BFFF ACCCON The contents of ACCCON principally dictate the activity of two regions of memory a 3000 to amp 7FFF b amp CO00 to amp DFFF 128 Kbyte RAM The RAM is functionally split up into two regions The main region supports the language workspaces buffers etc and provides the bit mapped screen The second region provides four 16K Sideways RAM segments These are link selected into ROM locations 4 5 6 and 7 They may be deselected reinstating the ROM sockets in chunks of 32 Kbyte Within the main 64 Kbyte region the lower 32K is used within the amp 0000 to amp 7FFF region of the CPU memory map as shown in figure 1 The upper 32K is split up into three self contiguous regions The largest portion of this is a 20 Kbyte region designated LYNNE This can be overlayed on the region a of main memory When bit D in ACCCON is set the CRT controller will display the contents of LYNNE When bit D is cleared the region a of main
76. ue 1 67 Master Series Service Manual C nos Location Sheet 51 9 5 2 52 9 8 53 9 7 1 54 9 7 2 55 9 6 2 56 9 6 2 57 58 59 9 6 2 60 9 8 1 61 8 2 2 62 8 1 2 63 8 1 2 64 8 0 2 65 9 2 2 66 9 1 2 67 9 4 2 68 9 0 2 69 9 0 2 70 9 2 2 71 9i 2 72 9 1 2 73 9 0 2 74 75 9 4 2 76 9 4 2 77 D3 2 78 3 7 1 79 6 4 2 80 5 4 1 81 Ty 1 82 dus 1 83 8 5 84 8 6 1 85 86 8 5 87 8 7 1 88 8 8 1 89 90 91 25 13 1 92 2 6 1 68 Issue 1 Master Series Service Manual D nos Location Sheet 1 id 2 2 8 2 3 1 2 4 5 D l 2 6 6 4 2 7 575 2 8 6 8 2 9 EZ 2 10 7 2 2 11 9 4 1 12 13 14 6 4 1 15 6 4 1 16 6 4 1 17 8 5 2 18 8 5 2 19 845 2 20 8 6 2 21 9 6 2 22 9 6 2 23 6 4 2 24 6 4 2 Q nos Location Sheet 1 157 2 2 5 8 2 3 6 8 2 5 7 6 2 6 7 6 2 7 8 8 9 1 9 8 9 1 10 9 9 1 11 8 7 1 12 8 8 1 13 14 8 6 2 69 Issue 1 PCB circuit diagram Sheet 1 3 m ii mt z T se 1 14 IRC mp gie TER sz T TE TU T Jm HER 0 D 1 3 t t 1 n 7 1 3 1 NTERNAL TUBE CONN 2 E 5 Mn dat dad COO cor d oat UT ugi FITMID OK UK VERON 1 te MAR mE m 3 LSM OE YO EOE TO FAWMAE
77. ystem 6522 A connection is provided from IC16 to a 6522 CA type connection Hence the interrupts thus generated are controlled by the 6522 control register Depression of either of the shift keys or the control key does not cause an interrupt to occur Keys are arranged as a QWERTY style keyboard with extra keys for a numeric keypad Ten additional function keys together with cursor control buttons etc are provided The BREAK key will reset the CPU and abort any access to the clock RAM chip To prevent accidental operation a mechanical lock is provided This is a plastic cam which is rotated through 90 degrees to stop the keytop from being depressed Keyboard Operation During free run mode the keyboard column lines are continually scanned by incrementing a counter decoding its outputs and pulling low a column line Any key depressed will cause the interrupt to be generated A signal KeyBoard ENable is generated to stop free running mode The counter contents are now loaded by CPU operation to determine on which row the key was pressed The rows are then individually selected to determine which key was pressed T IC16 is supplied with data from the slow data bus PAO to PA6 These are the slow bus connections PAO to PA3 are the column select inputs and PA4 to PA6 are the row select inputs PA7 is a three state connection whic

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