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Master Compact Service Manual

1. 1 NDEX 9 not WRITE ENABLE t 2 345673 9101 12 3 2 not SO 10 not TRACK 0 3 not SI 11 not WRITE PROTECT 4 not connected 12 not READ DATA 5 not MOTOR 13 not SIDE SELECT 6 not DIR 14 7 not STEP to Ov 5 16 17 18 19 2021 2223 26 25 8 not WRITE DATA 25 SK2 Printer 24 way Delta type D connector 12 11998765 3 2 1 1 STB 9 PD7 2 PDO 10 ACK 3 PDI 11 Not connected 4 PDZ 12 Not connected 5 PD3 T3 6 PDA to Ov 7 PD5 24 24 23 22 2 2019 18 17 16 15 14 13 8 PD6 PL13 Expansion connector 25way double sided polarised edge connector The information regarding connections to this port is contained within the main body of the manual 42 Issue 1 Master Series Compact Microcomputer Parts list An asterisk in the final Service Manual spare part through the spares department of Acorn Computers Ltd TEM PART NO DESCRIPTION ORY 2 3 0258 000 BARE PCB SS 1 4 3 6 0201 647 VIDEO PROCESSOR 7 8 0201 847 C MS O CTRL CF30050 1 9 10 2201 213 C MSI MEM SW CF30058 11 12 0201 845 C MSI P B C CF30049 13 14 0201 846 C MSI CRTC MUX CF30048 1 15 16 0258 011 IC SYSTEM ROM 17 18 19 20 0502 100 RES 10R C MF 5 0W25 21 22 0502 101 RES 100R C MF 5 0W25 23 24 0502 102 RES 1K0 C MF 5 0W25 25 26 0502 103 RES 10K C MF 5 0w25 27 28 0502 123 RES 12K C MF 53 0W25 29 30 0502 151 RES 150R C MF 5 OW25 31 32 0502 15
2. Service Manual TRANS BC309 PNP 04 DIODE SI 1N4148 D1 CONR 5W SKT DIN RA DOM SKT7 CONR 6W SKT DIN RA PCB SKT9 CONR 5W SKT DIN RA PCB SKT6 21 CONR 2W WAFR 0 1 ST PCB 1 PL CONR 3W WAFR 0 1 ST PCB 2 P 12 CONR 2W SHUNT 0 1 2 P 12 SKT IC 8 0 3 NORM 1 1C24 SKT IC 16 0 3 NORM 2 IC5 9 SKT IC 24 0 6 NORM 1 IC13 SKT IC 28 0 6 NORM 6 IC14 17 23 29 38 49 CONR 5W SKT HSNG 0 1 PCB 1 SKT5 CONR 17W SKT HSNG 1 PCB 1 SKT4 CONR 25W SKT D RA E2 54 1 SKT1 CONR 9W PLG D RA E2 54 1 PL8 CONR 24W SKT DELTA RA PCB 1 SKT2 PHONO SOCKET RA PCB SKT8 CONR 26W PLG 2ROW 2 5mm 1 PL6 CONR PWR SKT 2mm CTR PIN 1 PL2 XTAL 16 000MHz HC18 U 1 XL1 SCW M3x12 PAN HD POSI 6 FOR ITEMS 196 198 amp 200 Master Series Compact Microcomputer 218 219 0882 902 NUT M3 STL FULL Z PAS 220 221 0882 972 WITH ITEM 217 222 225 0882 985 WSHR M3 PLN NYLON WTTH TTRM 217 The following items are also available Service Manual S 6 USE EM 217 W TH 6 USI WSHR M3 SPRF IT STL L DTR HAST but are n
3. Service Manual the Peripheral Bus Controller IC26 is used to buffer the data bus It also isolates many parts of the system from each res Or improve reliability It may disguise data bus failu Be sure not to assume that any node is connected to any ther unless you have checked it This particularly applies to the SAA5050 nd all 1MHz operating components E g the User VIA going down top the System VIA could 26 Issue 1 Master series Compact Microcomputer service Manual 6 1 Switch on Connect the suspect microcomputer to an RGB monitor Connect the mains supply and switch on both the monitor and the computer One of the following will happen 6 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 Check that the power supply can provide five volts The centre of the plug is positive If the power supply has failed refer to the section regarding the monitor stand unit 6 1 2 The power supply is working the keyboard indicator is lit but nothing else happens E 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 very hot The 6845 V
4. SYNC 1 From amp COOO to amp DFFF in RAM a se A n V V R5 0 7 2 vV Y Is this de 57 Y 1 cycle an A mimm tein cd ili opcode fetch A V N i V NN uo cor Fao c3 Read Write Lynne Access main memory E V V p LA ve a re e manna AAA A Figure 2 This system allows for the screen bit map to be removed from the main CPU memory map of which it occupies a significant proportion It will however only work if the screen is being accessed by opcodes from a known region i e the MOS VDU drivers A mechanism is also provided to permit illegal screen access Bit X in ACCCON when set causes all accesses to region a to be re directed to LYNNE This occurs irrespective of the opcode address hence considerable care will have to b xercised in its use When cleared the memory map returns to its usual format In the same way that the BASIC variable HIMEM will always have the value amp 8000 when LYNNE is used it is desirable for the variable PAGE to have the value amp E00 irrespective of the current filing system 15 Issue 1 Master
5. Check the software if more than four envelopes are defined envelopes 4 15 use serial buffer space 6 9 3 Produces strange sounds This is most likely to be a software problem where the sound buffer is being accessed directly 6 10 Econet Econet can only be serviced properly by Econet service centres who will have the necessary test equipment t check the system thoroughly However there are a few simple things which can be checked without the test equipment Follow the Econet board circuit diagram in the Appendix 37 Issue 1 Master Series Compact Microcomputer Service Manual Check that the two connectors on the Econet module are correctly inserted The longer connector has two spare pins on the left of the PCB socket If the module is displaced and is plugged into one or both of these spare pins it will not work Check that the Econet module is installed and fitted correctly Check that NMI on the CPU pin 6 IC28 is not being held low 6 11 Non Volatile Memory Try a replacement PCD8572 IC24 socketed Check the power supply to 1C24 there should be 5v on pin 8 and Ov to pins 1 2 3 and 4 Check for continuity between IC24 and IC25 Pin 6 IC24 should be connected to pin 15 1025 and pin 5 IC24 should be connected to pin 14 1025 Check the operation of IC25 the system VIA and change if necessary
6. Service Manual 7 Check that all data and address bus lines are clear of shorts between themselves 5V and ground 8 Check the RAS and CAS signals to the main DRAMs RAS and pin 16 CAS The main DRAM timing is shown in figure 8 2MHz N go sy Wi RAS eg EZ EC X x CAS nl AZ M MATIZ AZ MMUNIZ V ADDRESS ANA PZA LAN Figure 8 DRAM timing RAS and CAS should be good 4MHz square waves is stuck low RAS is generated from 4M and 8M by the D type CAS for the main DRAMs is generated from 2M i ICs 35 and 41 pin 5 x N m VAAN If one or both is missing IN gated by a NAND gate in IC18 with DRAMEN and finally gated with 4M through another NAND which IC8 prn 9 nverted by then check for shorted tracks Remember the DRAMs can be destroyed if RAS IC10 to give phi2 nables the main RAM inm TE 9 Check the multiplexed address lines into the main DRAMs ICs 35 and 41 pins 6 7 8 10 11 12 13 and 14 The address lines should switch after RAS with an approximate 20ns hold time Also check that the address lines are correctl y switching after phi2 as shown in figure 7 6 1 3 There is a sort of display with roll stripes 1 Check the MA And RA lines from the 6845 CRTC from MAO pin 4 to MA13 pin 17 inclusiv ing lines and or diagonal IC34 Ther The
7. 0742 086 IC 74LS86 TTL 14 0 3 0744 086 IC 74ALS86 TTL 14 0 3 0742 139 IC 74LS139 TTL 16 03 0749 139 IC 74HCT139 CMOS 16 03 0742 156 IC 74LS156 TTL 0742 163 IC 74LS163 TTL 16 0 3 0744 163 IC 74ALS163 TTL 16 0 3 0742 174 IC 74LS174 TTL 16 0 3 0742 244 IC 7415244 TTL 20 0 3 0742 251 IC 74LS251 TTL 16 0 3 0749 251 IC 74HCT251 CMOS 16 0 3 0742 257 IC 74LS257 TTL 16 0 3 0744 257 IC 74ALS257 TTL 16 0 3 0742 259 I 74019259 TTL 16 0 3 0744 259 IC 74ALS259 TTE 16 0 3 0742 373 IC 74595373 TTL 20 0 3 1 0744 373 IC 74ALS373 TTL 20 0 3 0747 030 IC 74HC30 CMOS 14 0 3 0748 000 IC 74F00 TTL 14 0 3 0749 253 IC 74HCT253 CMOS 16 0 3 0770 386 IC LM386 AUDIO AMP 0780 239 TRANS BC239 NPN 11C37 IC4 LIC33 OPTION OPTION 1C31 OPTION IC11 OPTION IC45 IC27 3 2 1C39 40 ICA2 QT 2 3 Master Series Compact Microcomputer 163 164 165 166 167 168 169 170 172 75 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 21 0 WN ND MN NN ND N A DOH 0780 309 0794 148 0800 001 0800 002 0800 004 0800 050 0800 051 0800 070 0800 108 0800 116 0800 124 0800 128 0800 481 0800 484 0800 300 0800 313 0800 365 0800 611 0801 300 0801 001 0820 160 0882 124
8. cessary Carefully turn the unit onto its side undo the screws holding the cable clamp in position and lift it free Unplug the IDC connector from the Disc Drive and untwist the cable so that it is flat all the way along Carefully pull the cable from outside the unit and thread the IDC connector through the slot in the base of the unit pulling the cable free Feed the new Data Cable through the slot on the underside of the unit ensuring it is flat all connector is correctly oriented the way along and that the Keyboard Processor Twist the Data cable over as shown below in order to correctly orientate the IDC connector for connection to the Disc Drive 5 IDC Connector E P ed R A A ZA lay Data Cable a q Cable Clamp Fixing Screw Keyboard Processor Connector md Figure 5 Note Ensure that the data cable clamp is re fitted on the cable as shown in order to prevent the cable from snaring on the underside of the Disc Drive Insert the screws into the clamp from the underside of the unit Monitor Stand 54 Issue 1 Changing the Disc Drive drive Screw the pillars in over tighten them Before fitti Unplug the IDC connector and the 5 12 Volt connector from the Disc Drive Turn the unit onto its side and undo the four screws holding the Disc Drive support pillars take care not to drop the disc drive Lift the drive out of the
9. Joystick Port A 9 way ex wh ternal devices It is D type plug PL8 is provided for connection to compatible with existing ATARI type Joysticks ose digital outputs are converted by the operating system into suitab ADVAL s to emulate BBC analogue joystick operation 22 Issu le e 1 Master Series Compact Microcomputer Service Manual The port is derived from port B of the user VIA without extra buffering and may thus also be used for output as well as input The 6522 data sheet should be consulted for further details For applications requiring the use of the USER PORT as used in other BBC computers the three signals that are not provided on the joystick port PB5 PB6 and PB7 are available on the expansion port If link PL7 is made 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 E x p a n s i o n C o n n e c t o r This connector provides various signals suitable for connection to external peripherals
10. The full description of it is found in the manufacturers data sheet It is provided with a reference clock of 4MHz from central timing The output is filtered as described in the section Audio Circuitry Non volatile memory 128 bytes of non volatile memory are provided by IC24 This is a serial access device which operates on a special Inter integrated circuit serial bus known as an I sguared C bus This bus is emulated by lines PB4 and PB5 on the system VIA The write cycle time for this device is determined by RI and C2 The PCD8572 data sheet should be consulted for further details It is an Electrically Erasable and Programmable Read Only Memory EEPROM or E squared PROM This device is socketed due to its finite life and the guarantee is only valid for the PCD8572 working on delivery The use of this device means that battery backup is not required 19 Issue 1 Master Series Compact Microcomputer Service Manual for retention of non volatile memory System VIA A 6522 allows several sources to create maskable interrupts The sources are a CRTC vertical synchronisation b CRTC light pen strobe c Keyboard key detect It also provides the previously mentioned slow data bus Port B on this device generates and reads a number of internal hardware strobes These are as follows Port B Data i i Strobe T s Active
11. 1C4 on the 34 Issue 1 Master series Compact Microcomputer service Manual 6 Check that a strobe pulse appears on IC7 pin 39 for every character transmitted If not then check all address data and control p ins on the User VIA 7 Check that a strobe pulse is found inverted at pin 11 of the 7438 IC3 and true at pin 8 of the 7438 1C3 6 8 Expansion connector 1 Does the system work correctly without any peripherals fitted to the expansion connector If not check operation of the main computer before attempting to use such cartridges 2 Check the external hardware VERY CAREFULLY As the expansion port has direct connections to various system buses strange faults can be Simulated by external hardware 3 Check the software VERY CAREFULLY Similar comments apply to item 2 4 Check that there are no shorts on the edge connector The polarisation slot on the edge connector should avoid such problems but if the external connector is mounted squint such shorts could occur 5 Is the external connector attached the correct way round It may be possible to fit it in either of two positions 6 Is the edge connector excessively worn for example gold plating worn through 6 9 Sound Output 6 9 1 Will not work at all 1 Is the speaker connected 2 Check that the speaker has not blowm 6 9 2 Will not work with all envelopes
12. 5 inch disc drive is provided as standard for MFM discs The hardware will also support FM recorded data but the standard software provided will not support FM encoding 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 It will also be necessary to fit the ANFS ROM to one of the internal ROM sockets The daughter board used 1 Issue 1 Master Series Compact Microcomputer Service Manual is the same as for the Econet upgrade in the Master 128 Microcomputer Centronics Printer Port Connection is provided for the standard parallel printer port configuration Serial Port An RS232 standard interface is available as an optional upgrade This upgrade may be achieved by plugging the relevant ICs into provided sockets no soldering is required and it is not necessary to remove the PCB from the case Joystick Port A connection to an Atari type joystick is provided This has a 9 way D type plug The Machine Operating System reads the values Poj from the joystick in such a way to maintain compatibility with software for previous machines that used analogue joysticks and an Analogue to Digital Converter ADC 50 way Expansion Connector This allows the connection of many external items to the computer Many connections to the various system
13. Level I c POpPoH 0h a Non Vol Ram Serial Cik Non Vol Ram Serial Data Input Output Sound chip select Keyboard enable CO Screen control Ci Signals Caps Lock indicator Shift Lock indicator DG PS DG DG PX 56 4 M OJ 54 MKK KKK AE M M PROJ gt lt 9 5X M 4 M U X GUUTUUUKM PRRPRPOOKS PROOF Ojm x p E BR EH KO EH Figure 5 20 Issue 1 Master series Compact Microcomputer service Manual 5 4 External I O 1MHz External 1 0 Screen Output There are two chips primarily responsible for providing she screen output 0 6845 IC34 b Acorn proprietary VIDPROC IC16 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 available options are shown in figure 6 Video Data Formats Mode Format Reserved Memory z asi Pixels Byte Bytes e 0 8 20K LONE 4 20K E DG 2x 2 20K 3 8 16K RESTO WARS 4 8 10K U 5 x 4 Er ze 10K if 6 xx 8 ES 8K 7 z Teletext 1K 3 128 8 20K 129 4 20K 130 Zi A 2 20K Reserved 131 ae B 20K gt i in 132 8 3 20K LYNNE 133 4 20K 134 bese i 8 20K 135 o Teletext 20K Figure 6 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 s
14. TWA EN ROM SLOT To BE 1 19586 AMR EMS Te ACCESSED VIA THE EDGE CONNECTOR EL ov NF av 188 Dere DESC OK CHANGE DAN CHKE 5 R E COPYRIGHT 1386 TITLE ALL DIMENSIONS N mm UNLESS OTHERWISE STATED Copyright of this a reserves by ACORN COMPUTERS ACORN COMPUTERS Lio 86 MAIN PCB CIRCUIT DIAGRAM SHEET 1 of 1 LTD Hh rs issued on cosibaos thal it is nol copied reproduced ale anla without ihe consent in wntng of ACORN COMPUTERS LTD ACORN COMPUTERS Ltd Ag 0158 000 C ge nn or dizciosed io 2 tiie nany either wholly r in part CAMBRIDGE CA1 SIN HOLE No TOL DECIMAL Wo TOL ANGLE TOL E Ta AC IC 20 CF 300 8 ORAM 4464 48 ID 32 30 CF 10058 la j 28 ROMI EPROM A British Broadcasting Corporation Master Series Compact Microcomputer Service Manual Monitor Stand Section 46 ACORN COMPUTERS LTD MASTER COMPACT MONITOR STAND SERVICE GUIDESECTION SECTION 1 SERVICE INSTRUCTIONS SECTION 2 DISC UPGRADE INSTRUCTIONS Monitor Stand 50 Issue I This manual is intended to provide information for service engineers and ACORN dealers who will be servicing the Master Compact Computer No part of this manual is to be copied or communicated to persons other than those engaged upon service work for or on behalf of ACORN Computers WARNING DANGEROUS VOLTAGES EXIST INSIDE THE CASE OF THE MONITOR STAND QUALIFIED PERSONNEL ONLY SHOULD ATTEMPT TO REPLACE PARTS COMPONENTS IN THE MONITOR STAND ENCL
15. The signals provided are as follows Pin Side a Side b solder side component side 1 SCREEN 0v SCREEN 0v 2 5v A a j 5v 3 ATI3 MEE A10 4 NOT RST Neri CDI 5 AA15 CENAR RZA meme All V ME 3T 6 A3 TORS A9 7 A13 CD7 8 A12 ES ck CD6 PER 9 phi 2 OUT B CD5 to Far 10 not connected CD4 Co 11 not connected LPTSTP 12 B READ NOT WRITE i BAT 13 NOT NMI BA6 14 NOT IRQ f BAS 15 NOT INFC BA4 16 NOT INFD BA3 17 AA14 i E BA2 18 NOT 8MHz i BA 19 0v BAO 20 PB old user port CDO 21 PB6 old user port CD2 22 PBS old user port CDI POLARISATION SLOT x 24 Ov Ov 25 SCREEN Ov l SCREEN 0v Figure 7 Serial Port The serial interface is not fitted as standard The modification to fit the serial interface only requires the insertion of the relevant ICs into 23 Issue 1 Master Series Compact Microcomputer Service Manual their sockets No soldering is therefore required 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 data 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 Buffer The RS232 data and control lines are
16. and WG pins ns 22 and 21 If not then check all connections to the 1772 IC6 and the 74LS174 IC1 the signal path of WD IC6 pin 22 to the connector disc drive must be connected at this stage as pull up resistors for the line driver outputs are within the high with low going transitions 5 Follow the signal path of WG IC6 pin 21 disc drive The output should be to the connector Note a disc drive must be connected at this stage as pull up resistors for the line driver outputs are within the disc drive The output should be normal 6 6 7 Dal 1 Check all connections to the 7415174 ICI 2 Check ly high with low going transitions ta can be read and written correctl be selected out of two y but only one disc drive can that only one drive select output IC3 pins 3 and 6 6 7 Parallel printer port Ys is a logic LOW from the 7438 1 If the fault only shows up with a custom printer driver test the softwa re carefully first 2 Check the printer with another computer i E f possible 3 Check the computer with another printer i 4 Check that pin 40 on the User VIA IC7 is not short circuited to 5V possible has a pull up to 5V R14 but 5 Check that data appearing on Port A of the VIA IC7 pins 2 to 9 appears outputs of the 7415244 buffer
17. buffered by a MAX232 IC This device produces the necessary voltages required for RS232 operation from a single 5v supply The clock for the serial system is derived from the 16Mhz clock by IC9 74ALS169 acting as a divider 2MHz External 1 0 One peripheral device operates at 2MHz This is the ECONET connection This requires an extra hardware upgrade Connection is made to the ECONET by a five way DIN connector mounted on the main circuit board The interface electronics including the 68B54 line drivers receivers and chatter disconnect components are mounted on a separate circuit board This board has two connectors a A 5 way connector which has a one to one connection with the DIN connector b A 17 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 24 Issue 1 Master Series Compact Microcomputer Service Manual 6 Fault finding This section goes step by step through fault finding in each section of hardware It should be studied in conjunction with the circuit diagram and component location tables in the Appendix If any part of the machine is suspected of being faulty the following points should always be checked first 1 no loose connectors and broken cables 2 no broken or shorting track
18. buses are provided as are the signals required for external paged ROMs 12 Issue l Master Series Compact Microcomputer Service Manual 5 2 Core machine Operation of the RAM and ROM is controlled by the Memory Controller integrated circuit The principal function of this device is to control the memory paging structure Memory Map The 65C12 can directly address 64K locations As over 1 2 Mbyte may be resident depending on the users configuration a paging scheme is implemented to allow access to it The basic memory assignment is as follows PA A eS lt EFFFF SS o bn yl lt amp FF00 X Memory I O OR ROM Mapped 2 2 2 2 2 lt amp FE00 1 0 pee Bees oe ai pol amp E000 m amp C000 ROM Sideways RAM 2 2 amp 8000 RAM Shadow RAM REGION a lt 3000 RAM 7 lt 0000 Figure 1 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 RR TST IEJ ITU 36 X E D The contents of ROMSEL dictate the selection of memory which res
19. is checked carefully against the diagram NOTE Some Monitor Stands depending on the Model will have the the Mains Input Output connectors fixed to the unit with rivets rather than screws and washers Changing the Power Supply Refer to figure 2 above Undo the four fixing screws on the top of the PCB U the PCI nplug the Mains input connector the DC output connector and the Earth Tag Lift the PCB free and fit the replacement Note Ensure that E firmly B is secured properly and that all of the connectors are re seated in their sockets NOTE Some Monitor Stands will be fitted with a different type of power supply to that shown in Figure 2 Although the voltages are the the layout of the cables differ as shown below Sam Disc Drive Power Connectors a oc Output Connector Monitor Stand 52 Issue 1 Low Voltage components cables 5 Volt Supply Cable This lead supplies 5 Volts to the keyboard processor unit and is part of the DC Power Cable How to replace this is described below Checking Replacing the DC Power Cable Unplug the DC output connector from the power supply board The volt lead can be checked from the plug to the pins in continuity of the 5 the connector using below If the 5 Vo described Note At lt cable is found to be open circuit then proce the pin out diagram of the connector shown
20. is driven active low when a row column combination describes a depressed key R19 to R26 The keyboard row input connections are normally held high by pull up resistors If a key is depressed it will cause the appropriate row connection to be pulled low when its column is selected CA2 Connected to the system VIA this output will cause the VIA to generate an IRQ The line will be active low when an active key is detected nKBEN Generated by the system VIA this line is taken low when scanning the keyboard matrix 1MHz This is the timing reference 18 Issue 1 Master series Compact Microcomputer service Manual The Keyboard Matrix The keys are physically arranged as a QWERTY type keyboard with 10 function keys 4 cursor control keys and a 19 key numeric keypad The matrix is as follows CO C1 C2 C3 ca C5 C6 C7 C8 C9 C10 C11 C12 curs RO ESC fl 2 f3 5 6 8 9 rt 4 5 2 lt gt 2 2 Ea RI TAB Z sp V B M i copy 0 zt 3 WE 3 CEF R2 SHIFT S C G H N L H del 4 x LOCK s4 t a ue d R3 CAPS A x F Y J K O ret del LOCK amp curs SE wi R4 1 2 D R 6 U P up ret r 8 curs R5 0 W ET 7 I 9 0 _ down 8 9 curs R6 Q 3 4 5 f 8 7 left 6 7 R7 SHIFT CTRL Figure 4 Sound Generator The sound generator is an SN76489 device Three sound channels plus one pseudo random noise channel are provided
21. 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 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 16 Issue 1 gt mel ilmini daf wa Master Series Compact Microcomputer Summary of RAM memory map The 64K of DRAM is distributed as follows ADDRESS 9000 8000 0000 Figure 3 A further 64 Kbyte amp 8000 to amp BFFF o a a a recano 3000 DFFF gt With C000 Y active 8FEF gt gt 8000 RAM active E 20 vh 0000 XN uu M Bits in ACCCON Service Manual CPU ADDRESS of RAM is available as four pages of 16 Kbyte from 17 Issue 1 Master Series Compact Microcomputer Service Manual 5 3 Internal I O 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 4 During idle free run mode pr
22. to the left of the CRTC IC34 to make sure correct addresses ar n the CPU and the shown on that the being generated Any line stuck high o shorting to another pin will give strange screen effects r low or Note MA13 IC34 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 IC34 to the CRTC Multiplexer 1C46 actually get there 3 Check that the lines CO and Cl from the 7415259 IC31 pins 4 and 5 to the CRTC Multiplexer change at least once if you switch between modes i Check that the lines from the CRTC MUX 1046 to the DRAMs are with no short or open circuits 6 2 Sideways RAM 1 Check all connections to the memory address multiplexers 2 Check RAS and CAS at the DRAMs see figure 8 6 3 Video IC46 pins 38 and 39 are properly connected and correct To debug the video both different types of monitor should be connected RGB and composite 6 3 1 The display scrolls vertically round the screen Does it occur on RGB and Composite video 1 If so check VSYNC is correct on the CRTC 1034 pin 40 2 Then follow the signal through the exclusive OR gates 1020 where it is combined with HSYNC any node then ther levels at If the signal does not make good l
23. which can be used to isolate it from IRO Note the system VIA IC25 generates an interrupt every 100th of a second If this interrupt is not cleared by the operating system each time it occurs the IRQ line will appear to be stuck low This could occur if some other installed software is faulty or if an address or data line to the VIA is faulty 6 1 8 Not all keys work on the keyboard 1 If more than one key is affected check for a faulty connection to the keyboard or a broken track in the middle of a row or column of the keyboard matrix 2 If one key only is affected check for a broken track at the end of a row or column in the keyboard matrix 3 If it is not possible to find track faults try replacing the whole keyboard assembly It is not possible to replace individual keys on this type of keyboard and it will be necessary to replace the whole keyboard 6 1 9 The computer works but random dots or characters appear on the screen 1 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 or text enough to fill a screen and repeat the test Any fault showing it
24. 2 RES 1K5 C MF 5 0w25 33 34 0502 221 RES 220R C MF 53 0W25 35 36 0502 222 RES 2K2 C MF 5 OW25 37 38 0502 273 RES 27K C MF 5 0W25 39 40 0502 330 RES 33R C MF 53 0W25 41 42 0502 331 RES 330R C MF 5 OW25 43 44 0502 392 RES 3K9 C MF s 0W25 45 46 47 48 0502 680 RES 68R C MF 5 0W25 49 50 0502 683 RES 68K C MF 5 0W25 43 REMARKS IC16 IC22 1C48 IC26 R9 12 34 IC49 SOCKET R5 R27 38 44 828 45 52 55 R19 26 67 R1 3 R29 31 47 49 54 R36 40 50 R14 15 17 48 53 56 R2 8 32 35 R41 43 R33 46 57 R13 51 R37 39 61 66 R4 column indicates that the item is available as a Issue 1 Master series Compact Microcomputer 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 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 97 98 99 100 101 102 103 105 106 service Manual R58 60 Cts 85 1921 05 39 C6 C29 C4 C2 5 C27 C13 18 C26 C16 CS 7 015431 IC6 IC24 SOCKET 1C35 36 41 47 1C15 1C30 1C28 107 25 0502 820 RES 82R C MF 5 0W25 0622 220 CPCTR ALEC 22u 16V
25. AD British Broadcasting Corporation Master Series Compact Microcomputer Service Manual Part No 0458 002 Issue 1 October 1986 Master Series Compact Microcomputer Service Manual BRITISH BROADCASTING CORPORATION MASTER SERIES COMPACT COMPUTER SERVICE MANUAL SECTION 1 KEYBOARD and PROCESSOR PAGE 1 SECTION 2 MONITOR STAND PAGE 46 Issue 2 Master Series Compact Microcomputer Service Manual SECTION 1 BRITISH BROADCASTING CORPORATION MASTER SERIES COMPACT MICROCOMPUTER SERVICE MANUAL KEYBOARD and PROCESSOR Bl Issue 1 Master Series Compact Microcomputer ithin this publication the term BBC British Broadcasting Corporation Copyright Acorn Computers Limited 1986 Neither the whole or any part of the information contained this manual may be adapted or reproduced in any the prior written approval product described in material form except with Service Manual is used as an abbreviation for TI O the of Acorn Computers Limited Acorn Computers The product described in this manual and products for use with it are subject to continuous development and improvement All information of a technical nature and particulars of the product and its use including the information and particulars in this manual are given by Acorn Computers in good faith However it is acknowledged that there may be errors or omissions in this manua
26. AX 0621 470 CPCTR ALEC 47u 10V AX 0629 010 CPCTR CPLT 10n 30V 80 0630 100 CPCTR CPLT 1n0 30V 10 0630 220 CPCTR CPLT 2n2 30V 10 0631 010 CPCTR CPLT 10p 30V 2 0631 022 CPCTR CPLT 22p 30V 2 0631 033 CPCTR CPLT 33p 30V 2 0631 047 CPCTR CPLT 47p 30V 2 0631 100 CPCTR CPLT 100p 30V 2 0631 220 CPCTR CPLT 220p 30V 2 0635 470 CPCTR ALEC 47u 16V RAD 0680 004 CPCTR DCPLR 47n 20 0 2 P 0680 101 CPCTR DCPLR 100n AX 25V 0701 772 IC WD1772 FDC 5 25 0702 220 IC PCD8572 NV MEM 0704 105 IC 4464 DRAM 120nS 64Kx4 4 0705 050 IC SAA 5050 CHTR GEN 1 0706 489 IC 76489 SOUND GEN 0706 512 IC 65SC12 CPU CMOS 2MH 0706 522 IC 6522 VIA NMOS 1MH 0706 524 IC 6522 VIA CMOS 1MHz 0706 845 IC 6845 CRTC NMOS 1MHz 1 44 OPTION Issue 1 Master Series Compact Microcomputer 107 108 o JOU W NRO 120 121 122 123 124 25 Service Manual IC2 OPTION IC3 IC10 1C8 IC18 OPTION 1097 IC19 IC20 1 OPTION IC12 OPTION IC32 44 IC43 OPTION IC 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 004 IC 74S04 TTL 14 0 3 0748 074 IC 74F74 TTL 14 0 3 0742 000 IC 74LS00 TTL 14 0 3 0744 000 IC 74ALS00 TTL 14 0 3 0742 002 IC 74LS02 TTL 147 0 3 0742 014 IC 74LS14 TTL 14 0 3
27. DRQ transitions 6 3 The catalogue can be read but the entries are corrupted Check that C10 is fitted and of the correct value between IC6 pin 27 to Ov Are one or two disc drives present If two make sure that only one of or the directory 6 6 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 2 3 There may be a fault in the memory system Check that to the Memory Controller disc drive is at fault As 1 above with good logic levels 1C48 pins 21 If the fault persists to 28 then the the address inputs inclusive are sWitching Check that the 35 outputs the MA lines are Issue 1 Master Se ries Compact Microcomputer switching A good test here is to press each line in turn i multipl Check that the MA lines on Service Manual BREAK repeatedly and look at exers IC29 and IC33 1C48 are correctly connected to the address 5 Use a memory test program to validate memory This is rarely necessary as the memory chips are highly reliable 6 6 6 Data can be read correcty but cannot be written reliably 1 Is the disc formatted correctly 2 Has the disc been write protected 3 Check the disc drive on another computer 4 Check IC6 pi 4 Follow Note a normally that data transitions are appeari if possible ng on the 1772 WD
28. Earth Tegs Mains Inout Connector 5 12 Volt Connector Fig 2 The Mains Power Lead The Mains Lead supplied with the Monitor Stand has a moulded 13A plug top at one end and a moulded socket connector at the other The 5A fuse in the plug top should be checked for continuity and replaced if found to be faulty Also check the Mains Lead for continuity and replace if faulty The Mains On Off Switch Figure 3 shows how the Mains On Off Switch can be removed for replacement Note ensure the push on connections are re made as shown in figure 3 Only replace components with Acorn approved spares Monitor Stand 50 Issue 1 The Mains Auxiliary Output The Ma ins Auxiliary Output connector Can be located and dismantled as shown in figure 3 all wiring should be re made to match the colour code given 45Voll CobtefPiug SEZ Strain Relist gt a zn Au aha l A i 2 gt mor M lol m gore gt Z ARA S3 dul l A Moins Auxiliar y Brown Output E TON 2 A Moins ON OFF Swit asg BA des ae FIGURE 3 The Mains Fuse The Monitor Stand Mains Fuse is situated on the back of the unit as shown above If faulty replace only with a fuse of the correct rating Anti surge 3 15A HBC 250v a c e g Type T The Mains Input The Mains Input connector can be dismantled and changed as shown in figure 3 above again make sure that all wiring
29. IDPROC and RAM chips will always be quite warm Check for shorted PCB tracks 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 cured should still be replaced Their long term reliablility may well be impaired 3 Check the 16MHz oscillator output IC10 pin 2 and check that it is reaching the VIDPROC IC16 pin 8 The signal should be reasonably clean 4V peak to peak If not then check the crystal controlled oscillator circuit formed by half of IC10 and X2 Warning if the system 16MHz clock does not work the DRAM RAS and CAS lines could be held low This can make the ICs heat up causing permanent damage If the oscillator is not working or the clock is not reaching the VIDPROC try to find the fault and repair it as quickly as possible Do not leave the computer switched on for more than 30 seconds at a time 4 Check the 1 2 4 and 8 MHz signals from the VIDPROC IC16 pins 4 5 6 and 7 respectively If any is missing or is not a clean square wave with TTL logic levels then replace the VIDPROC IC16 5 Check that there is a clean 2 MHz signal on the CPU clock input IC28 pin 37 If it is missing or incorrect then check for broken or shorting track 6 Check that the system ROM is plugged in 27 Issue 1 Master Series Compact Microcomputer
30. If all else fails check the RC timing circuit formed by RI and C2 38 Issue 1 Master Series Compact Microcomputer Service Manual 7 Hints and Tips Please advise us at ACORN of any hints and tips that you feel would be suitable for inclusion here Feedback from service personnel is particularly useful in this respect Use the North end of Cl in the Northwest corner for a Ov oscilloscope ground There is a large copper area to the Southwest of the PCB that looks like an earthplane It is actually 5v beWare of this 39 Issue 1 Master Series Compact Microcomputer Service Manual Appendix 40 Issue 1 Master Series Compact Microcomputer Connector Pinoute SKT8 video out phono socket outer ground inner video PL2 power input power socket outer Ov inner 5v SKT9 RGB 6 pin DIN Red Green Blue Sync Ov 5V O OUT Ww N HH SKT7 RS232 5 pin domino DIN A Data in B Data out C Ov D CTS T pme SKT6 ECONET 5 pin DIN 180 1 Data 2 Ov 3 Clock 4 Data 5 Clock 5v red ev green syne blue Gy RTS data in D CTS data out clock data clock data Ov 41 Service Manual Issue 1 Master Series Compact Microcomputer Service Manual PL8 Joystick 9 way D type plug 1 PB3 6 PBO 2 PB2 7 5v gt a Ov GE 4 PB4 9 CB2 LPTSTB 5 CB if connected 7 6 9 SKT1 Disc drive 25 way D type socket
31. ORAM 45 DRAM sibi AAG ar z S7HE POWER INPUT up liens ta It a FSINE vm ea e gra je la 4 res He 214 25 7 PRMCTZ5I DRAM dibi aks LM 38 RAT 1808 c Je iero Raf im ES Hi ki lu Ta 5 la 1 lo e CHAM ZETOR use Je i t es ra 1 j EER EHS 1 g Ca ELIA Cor E K EER e i o 2 iex pra a or RSL COEN v1 2E SKT 2 PRINTER e Al ai a kJ GE 2 Form faso Mazs i M Li LS i Tht sla co m M ip p 19 9 Bac IS amma PB7 20 X CDO 21 2 Cb o a PLB EE JQ STICK 23 123 POLARISING TET T z SLa 4 HD Pi o i Hizm 3 1 i i 25a 255 oo w RS 232 74808 1044 aim C26 16 MHI 41 155 TAnF xLi zv zv3 nr pi SERCLK NOTES CHRO LINK MADE WiTH TRACK O xat sY DOLINA MADE WITH MOLEX PINS AND W t BRUNT LINE SHOWS NORMAL LINK 6 i A i j Te i i i e i i 1 NC NOT CONNECTED COMPONENT PIN i PLE KEYBDARO CONN R12 Tan Tazo Fare Teza A 1825 1826 Nal le BELERI L 10 fion POK 10K n 10 DOK 100K al NF COMPONENT NOT REQUIRED FOR NORMA CIRCUIT OPERATION TP TEST POINT Pi SELECTS Ca ROM SIZE NORTH 64 SOUTH 28K 2 1 SOUTH SELECTS C34 D BE amp v E v5 2 5394 Eto 208 JADON 492 AND ALLOWS
32. OSURE S IMPORTANT THE MONITOR STAND MUST BE EARTHED Any service work involving components wiring and assemblies associated with hazardous voltages or safety earth connections should only be undertaken by suitably qualified service personnel On completion of such work and to ensure product safety is in no way degraded the unit should be subjected to the appropriate safety test s before being returned to the customer namely Earth Continuity A current derived from an AC source with no load voltage not exceeding 12v shall be passed through the earth conductor of the power supply cord to all accessible metal parts intended to be earthed The measured resistance shall not exceed 0 1 Ohms Excluding the resistance of the supply cord Insulation Withstand test A test voltage of 1 5Kv A C or 2 1Kv D C shall be applied between Live and Neutral pins of the supply cord connected together and the earth pin by means of a suitable insulation tester E G AVO Type RM 215 L 2 or similar for a minimum of ten seconds The unit shall show no flash over or breakdown during the test NOTE As the requirements of some customers may differ from the BS Standard some Monitor Stands may be fitted with a metal screen held in place by four fixing screws around the Power Supply This screen must be re fitted if the Power Supply is replaced This manual will be subject to change from time to time no responsibility can b
33. Series Compact Microcomputer Service Manual This is achieved by providing a filing system workspace as follows Bit Y in ACCCON when set causes 8 Kbyte of RAM referred to as HAZEL to be overlayed on the MOS VDU drivers i e from C000 to amp DFFF 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 responsible for resetting the Y bit as no hardware is provided for this purpose The remaining bits in ACCCON are used to control various peripheral systems The bit ITU in ACCCON when set enables the CPU to access the internal second processor rather than the external one The bit IRR in ACCCON is InterRupt Request When set this bit causes an open drain output to pull the CPU NIRQ pin down to Vss ROMSEL E The contents of ROMSEL determine the paging of memory in the 16K region 8000 to amp BFFF One of sixteen unique 16 Kbyte ROM memory segments may be selected In this way fewer connections to the controller logic are required to select a given ROM although the power dissipation will be increased if all the ROMs in one column are inserted A chip select will be driven low if an access to one of the on board segments is required An output enable is turned active low during the CPU phi2 period depending on which segment is required The segment
34. a Cable Mains ON OFF Sw Disc Drive 1 Pillars Keyboard Processor Connector Earth Tags Mainsinput Connector SE l P 5 412 Volt Connector Do fu Fig 2 Before fitting the second Disc Drive it is necessary to remove the existing Disc Drive Data Cable and fit a dual Disc Drive cable for connection to the second drive Monitor Stand 58 Issue 1 Carefully turn the unit onto its side undo the screws holding the cable clamp in position and lift it free Unplug the IDC connector from the Disc Drive and untwist the cable so that it is flat all the way along Carefully pull the cable from outside the unit and thread the IDC connector through the slot in the base of the unit pulling the cable rree Install the Dual Drive Data Cable along the same path used for the single drive cable just removed When the new data cable is inserted and pulled Drives Refer to Figure 3 below Fixing Screw Keyboard Processor Connector Figure 3 Cable Clamp through the slot in the base of the unit it must be twisted over in order to correctly orientate the IDC connectors for connection to the Disc IDC Connector Data Cable Note Ensure that the data cable clamp is re fitted on the cable as shown above in order to prevent the cable from snaring on the underside of the Disc Drive Insert the screws into the clamp from the
35. description Introduction Core machine ternal I O ternal I O gt Ww N EP ni Ext Fault finding Switch on Sideways RAM Video Joystick Port Serial Port Disc drive interface Parallel printer port Expansion connector Sound output 0 Econet 20 0 301014 W N E 11 Non Volatile Memory Appendix Service Manual Issue 1 Master Series Compact Microcomputer Service Manual 1 Introduction This manual is intended and repair faults on the to provide the information required to diagnose B BC Master Series Compact Microcomputer The information contained in this manual is aimed at servic ngineers and Acorn dealers who will be servicing the BBC Master Series Compact Microcomputer on behalf of Acorn Computers Ltd 6 Issue 1 Master Series Compact Microcomputer Service Manual 2 Packaging and installation The microcomputer is supplied in a two part moulded polystyrene packing in a cardboard box It is supplied with a Welcome Guide Welcome Disc VIEW reference card VIEW ABC keyboard insert a Logotron LOGO guide and a guarantee card Ez 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 mic
36. e accepted for any errors and or omissions ACORN COMPUTERS Ltd can accept no responsibility for any loss or damage resulting from use of the information contained herein this does not affect your statutory rights in any way Monitor Stand 51 Issue 1 Introduction As there are no serviceable parts inside the Monitor Stand a first line level of servicing only is possible Basically this means that faulty cables and parts should be replaced rather than repaired Under NO circumstances should Users or Dealers attempt to fault find on the power supply Failure to comply with these recommendations will invalidate the warranty and could put users of the equipment at risk Dismantling The Monitor Stand Turn the Mains switch to the OFF 0 position and unplug the mains lead from the mains wall socket and then from the mains socket on the Monitor Stand Remove th 5 Volt lead from the Keyboard Processor unit Also disconnect the Disc Drive Data cable from the Keyboard Processor unit DO NOT DISMANTLE THE MONITOR STAND WITH THE MAINS LEAD PLUGGED IN EVEN WITH THE MAINS SWITCH IN THE 0 OFF POSITION THERE ARE STILL DANGEROUS VOLTAGES PRESENT Referring to figure 1 below lay the Monitor Stand on a flat even surface with the front of the unit facing towards you Placing your thumbs on the underside of the unit and your fingertips along the top pull the plastic fro
37. e driver IC5 comes out of it The driver could be faulty otherwise Check that the Tx CLK going into the ACIA is correct IC13 pin 4 5 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 Check 4 and 7 as above Check that data going into the line receiver IC5 comes out of it Check that the Rx CLK going into the ACIA is correct 1C13 pin 3 6 Disc drive interface 6 1 Refuses to work at all Check that both the signal connector and power connector are securely pushed home Try another disc drive if possible to eliminate the chance of a fault in this Try the disc drive with another computer if possible Check that the 1772 and 7415174 have valid logic 0 levels at their device select inputs 1C6 pin 1 and ICI pin 1 and that all data and address bus connections are present with no open or short circuits If 34 Issue 1 Master Series Compact Microcomputer either IC controller 1C22 pin 1 availabl 6 6 2 Th is not being selected FDCON and pin le then check that the disc software 4 FDC e drive select light comes on You cannot read a catalogue O E 6 6 4 The root Are the pull up resistors R9 R12 correct I
38. e the unit by reversing the dismantling instructions given above Note ensure that when the top case is re fitted the ventilation slots are at the back of the unit B Now that the upgrade has been completed it is advisable to do a functional test of the new disc drive For example check that Discs can be formatted and also that the drive will write to and read from discs without errors Note If necessary contact your nearest ACORN dealer for advice Acorn Computers Limited Fulbourn Road Cherry Hinton Cambridge CB1 4JN England Issue 1 September 1986 Monitor Stand 60 Issue 1
39. eck the address and ship select lines of the system V press CTRL F C prompt gt appears n and off nnections to and from the keyboard IC45 and the keyboard connector as these are quite reliable The Check TTL is available at the CSYNC polarity for that ICs are un The machine should now work C is printed on the screen IRO line on the CPU tion memory may have been set Turn the power off and on again whilst holding down the R key BREAK All previous configuration commands will be reset IC28 pin 4 but Cs 1C43 IC44 ikely to be at f this works then either connect up a disc drive disc in it or type incorrectly or 2 Check all connections to the keyboard 29 is faulty Then to but no gt prompt appears is not stuck in one logic then check the address and chip select lines of the system but the keyboard does not respond A C2 5x Issue 1 Master Series Compact Microcomputer Service Manual 3 If all else fails then try a different keyboard If this works look for broken leads and tracks on the original one 4 Check that the IRQ line IC28 pin 4 is not stuck low or high The memory controller 1C48 ACIA IC3 if fitted user VIA IC7 system VIA IC25 and PL13 edge connector all have direct connections to the IRQ line The latter part has a link LK4
40. ection 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 Special measures have been taken to ensure correct cursor operation in the Teletext modes 23 Issue 1 Master Series Compact Microcomputer Teletext The Teletext modes do not generate a bit mapped display The character graphics ROM within a SAA5050 device genera information within cell one B signals according to the desired character graphics Each byte of memory is therefore Just a RG th Service Manual but a character reserved memory space LoS definition of the character graphics symbol required Other SAA505X devices may be used when different languages are requir ly 1 Kbyte of memory is needed for either of the Teletext modes although 20K is reserved for it in mode 135 On ds The VIDPROC has to be re The 6845 is s occur after a character appropriate RGB signals start of screen signal is given a 1 5 byte time offset and SAA5050 programmed to use the SAA5050 RGB outputs till used to generate the cursor As a delay of 2 75 us w is read from RAM be
41. essing any key will cause an IRQ to be generated via the system 6522 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 NOT KeyBoard ENable is generated to stop free running mode The counter contents are now loaded by CPU operation to d j etermine on which column the key was pressed The rows are then ndividually selected to determine which key was pressed The keyboard support TTL chips are supplied with data from the slow data bus SAO to SA7 These are the slow bus connections SAO to SA3 are the column select inputs and SA4 to SA6 are the row select inputs SA7 is a three state connection which
42. fore outputting cursor data phase Th Hardware Scroll e 6845 start of screen address to an integral number of video th e VIDPROC has further adj adjusted to pixel accuracy the 6845 has to be programmed accordingly Scrolling may be achieved in any mode by re programm Ek the The the has a further 1 byte time offset to restore the correct ustment which allows for the cursor to be ing further down the memory map than the nominal start of screen Th an th is of course Causes the linear address generator to attempt to disp is out of the reserved video area To overcome scrolling is provided with a variable address end of screen which is effect hardware wrap around In out of screen RAM th do is modification to be used is controlled by two nodes CO and Cl effect when the address generator would otherwis lines lay attempt to access its addresses are modified to point to the gap between e original start of screen and scrolled start of screen When this is ne only the end of screen needs to be written over in RAM If this screen appears to roll over The amount of not done th ntir Video Output Two outputs are provided for displaying video data These are a b Composite video This is a lv peak to peak signal Digital Red Green Blue outputs These are approximately 75 ohm outputs
43. ides from amp 8000 to amp BFFF 13 Issue 1 Master Series Compact Microcomputer Service Manual ACCCON The contents of ACCCON principally dictate the activity of two regions of memory a amp 3000 to amp 7FFF b C000 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 selected into ROM areas Within the main 64 Kbyte region the lower 32K is used within the 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 and is sometimes referred to as SHADOW RAM 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 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 14 Issue I Master Series Compact Microcomputer Service Manual Wait until end i of CPU clock cycle gh Was the last cycle an gt PP opcode fetch gt
44. in figure 4 ed as full load current conditions the cable should give a resistance reading of less than 100 milli Ohms for each wire SG TWW DC Power Cable Figure 4 As the 5 Volt cable is part of the Low voltage DC output Cable Assembly th ntire assembly 5 12 Volt supply to must be replaced This cableform also carrie s the the Disc Drive s on the connectors shown in figure 2 above Having already unplugged the DC output connector from the power supply unplug the 5 12 Volt connector from the Disc Drive s Note the 5 Volt power cable goes through the back panel via a strain relief that grommet this can be pushed out of the back panel from inside the using a grommet insertion extraction tool Once the strain relief grommet is clear of the back panel pull the 5 Volt cable into the unit now possible to lift the cableform out of the unit and replace with a spare available from Monitor Stand Acorn Computers by reversing the above procedur 53 unit TENES es Issue 1 The Disc Drive Data Cable If Disc errors are continually occurring this may be due to a fault on the whether th cable is Disc Drive Data Cable The quickest way to determin faulty or not is to try a known working replacement Drive Cable as folloWs referring to figures 2 and 5 as ne Replace the Disc
45. l A list of details of any amendments or revisions to this manual can be obtained upon request from Acorn Computers Technical Enquiries Acorn Computers welcome comments and suggestions relating to the product and this manual All correspondence should be addressed to Technical Enquiries Acorn Computers Limited Newmarket Road Cambridge CB5 8PD All maintenance and service on the product must be carried out by Acorn Computers authorised dealers Acorn Computers can accept no liability whatsoever for any loss or damage caused by service or maintenance by unauthorised personnel This manual is intended only to assist the reader in the use of this product and therefore Acorn Computers shall not be liable for any loss or damage whatsoever arising from the use of any information or particulars in or any error or omission in this manual or any incorrect use of the product authorised dealers and This manual is for the sole use of Acorn Computers must only be used by them in connection with the product described within First published 1986 Published by Acorn Computers Limited 4 Issue 1 Master Series Compact Microcomputer BBC Master Series Compact Microcomputer Service Manual Contents Section 1 1 or O10101 0 a O DO O O O O DO O E Introduction Packaging and installation B Disassembly and assembly Selection links and Test Points Hardware
46. ng unit with associated memory and various input output devices for communication with external equipment 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 Dedicated hardware can be used to expand this almost indefinitely Further paged RAM through the expansion connector would also be possible Read Only Memory 64k bytes of ROM are provided as standard with this machine although this may be upgraded with later issues to provide 128k bytes of ROM as standard On board provision to extend the ROM capacity by 80k bytes is made although using external expansion this could also be expanded almost indefinitely Internal I O 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 sa a A 93 contact keyboard with 2 key rollover 3 Channel sound generator with additional noise channel Non Volatile memory 2 The Printer Port The Joystick Port Part of Expansion Port External I O Video display A 6845 CRT controller is provided to format the output for RGB Composite video is also provided Disc Interface Facilities to both save and retrieve data from standard Shugart connected media A 3
47. nt Check all connections to the VIDPROC IC16 Are the pull up resistors R29to R31 present and the correct values i Not all characters can be obtained Check all data bus connections the the PBC IC26 pins 21 to 28 5 Lines of normal size text appear cut in half Check VSYNC at the CRTC IC34 pin 40 6 Rounded characters appear unstable Check the components and signals around the 6MHz generator IC20 and IC21 7 Lines are broken up Check all connections to the PBC IC26 6 4 Joystick port 6 4 1 Gives incorrect readings on some or all channels 1 Check for continuity between PL8 and IC7 Are the connections to PL8 sound 21s 5v available at PL8 pin 7 and Ov at PL8 pin 8 Otherwise the joysticks will not function properly 3 Check that the software does not reconfigure port B of the user VIA IC7 as outputs look for any reference in the program to location amp FE62 the data direction register 4Try with a different joystick as joysticks are often badly abused and unreliable 5 Check the user VIA IC7 This IC is fairly reliable and replacement should be regarded as a last resort 6 5 Serial port 6 5 1 Does not work at all 1 Check that the upgrade has been performed correctly The basic machine does not include the serial interface and the upgrade should be checked carefully 2 Are the data format and baud rate settings the same as
48. nt panel towards you and at the same time downwards and away from the unit Once the front panel is removed turn the unit around and remove the back panel in the same way The side panels will now pull off the unit using the same technigue Plastic Side Piece Plastic End Piece Plastic Side Piece Gently Prise Apart To Facilitate Removal Ol inner Assembly H I a a Fig 1 Having removed the front and side panels as described above turn the unit over and undo the outermost screws on the underside of the case There may be four or six screws depending on the model you have Remove the screws and washers and put them in a safe place until required again Turn the Monitor Stand over the right way up with the front of the unit facing towards you Slide the top backwards and pull the main unit clear taking care not to damage the Disc Drive Data cable or the 5 Volt power cable NOTE t may be necessary to push the side panels of the top apart slightly to allow the main unit to slide clear Fixing Screws Connect 5 12 Vou Data Cable Slot 10C Connector Connector v 4 1 e sr 5 Volt Cable fe DC Output Connector Mains Input Disc Data Cabie Clamp Mains Fuse y Disc Drive Data Cable 0 Disc Drive Mains Auxilliary Output EM Mains ON OFF Switch ES MI gm Pillars Sas Keyboard Processor Connector
49. nverted If set North If set South Factory position NORTH If set North East tz AST in ned copper the RGB CSYNC signal This is necessary for certain monitors If change is required required position using a mini shunt will be inverted If set West it Factory cut circuit board track and or fit three pins and select the required wire ng 32k required allows system allows ROM containing but may change to SOUTH which may be adjusted as required a mini shunt ROM space banks 0 and 1 are assigned to the edge 32k ROM space banks 0 and 1 assigned to 1C38 Connector is made as a mini shunt which may be ROM containing 64k bytes of code If 128k bytes Factory position is currently n future production Connector is made as j Circuit board modifications necessary for fitting optional components TE VR1 a volume control potentiometer VR1 may be fitted the circuit board track joini is required for the loudspeaker If this modification is done ng two pins of VRI a preset first cut ted if required first cut the track under and L2 is used the tracks under L1 and FS1 A fuse FS1 may be fit FS1 on the PCB L1 L2 If further filtering Ll L2 on the main PCB must be cut Test Points TP1 MAX232 this pin sho TP2 MAX232 this pin should be between 5v and 10v Tes
50. ogic is probably a short in that area Note when VSYNC period 20ms is EXORed with HSYNC period 64 former Will pe difficult to spot within the latter A way of getting round this is to synchronise the oscilloscope from the VYSNC output of the CRTC 1C34 pin 40 and then examine the EXOR gate output Does it only occur on one of the video outputs 1 Is the CSYNC polarity link PL10 correct for your monitor 31 ius the Issue 1 Master Series Compact Microcomputer stir Service Manual 2 If it only occurs on composite video check that all the resistors R51 to 54 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 RGB check all the signals going to the back of the connector 6 3 2 The display is correct vertically but is broken into moving diagonal lines Does it occur on RGB and Composite video 1 If so check HSYNC is correct on the CRTC 1C34 pin 39 2 Then follow the signal through the exclusive OR gates 1C20 where it is combined with VSYNC If the signal does not make good logic levels at any node then there is probably a short in that area Note when HSYNC period 64us is EXORed with VSYNC period 20ms the former will have the latter superimposed upon it This will make the former appear to have glitches This should be igno
51. ot mounted on the printed circuit board 0201 248 EXPANSION CONNECTOR COVER 1 0158 0001 T KEYBOARD PCB ASSEMBLY 1 0258 001 CASE UPPER AVAILABLE AS SET ONLY 0258 002 CASE LOWER 0258 003 REAR LABEL 1 0258 004 TOP LABEL AVAILABLE AS SET ONLY 0258 005 BOTTOM LABEL 0258 007 POLY TOP SHELL 1 AVAILABLE AS SET ONLY 0258 008 POLY BOTTOM SHELL 0258 009 OUTER CARTON 1 0258 010 WELCOME UTIL DISC 1 0458 000 WELCOME GUIDE 1 0458 001 LOGOTRON LOGO BOOK 1 2201 138 VIEW REFERENCE GUIDE 1 0458 012 VIEW ABC KEYCARD 1 0800 080 CONR TERM CRIMP 4809C 2 SPEAKER CONNECTOR 0800 082 CONR 2W SKT HSNG 0 1 SPEAKER CONNECTOR 0835 001 LSPKR 16R 0 2W 40mmD 1 SPEAKER 0890 001 FOOT SO RUBR 12 7Dx3 5mmH 4 TBA KEYTOP SET 1 TBA RED KEYBOARD LED 3 TBA KEYBOARD RIBBON CABLE 1 gt mano naut PRoJECTION IF IN DOUBT ASK DO NOT SCALE TYPE M 36 9177 7406 7438 TELS IEG MAX 232 CPE WOITE a32 m 27k amp alas FAL Ta ALBIS USDA 3415371 3415139 6350 FEROE 207 SAA 5050 VIDPROC 2063 ROM EPROM 5 iii FEESE Ph yum E SO 1023 t Yre m ai Ala a m2 180 BYTE T4LSIA 74LSB6 41 50 F 30959 QM EPAQM PCDIST AGNI EB i ECONET MODULE lese 3 SKT 4 CF 30945 SE ROME FROM T6285 TaLSZES TLLSISE Tass 5845
52. ou Placing your thumbs on the unit and your fingertips along the top pull the plas front panel towards you and at the same time downwards and away from e front panel is removed turn the unit around and remove Plastic Side Piece Gerliy Prise Apart To Facilitate Removal Of inner Assembly Figure 1 EVEN Referring to figure 1 below lay the Monitor Stand on a flat even surface th the front underside of the ELO the the back panel in the same way The side panels will now pull off the unit using the same technique 57 Issue 1 Having removed the front and side panels as described above turn the unit over and undo the outermost screWs on the underside of the case There may be four or six screws depending on the model you have Remove the screws and washers and put them in a safe place until required again Turn the Monitor Stand over the right way up with the front of the unit facing towards you Slide the top backwards and pull the main unit clear taking care not to damage the Disc Drive Data cable or the 5 Volt power cable NOTE It may be necessary to push the side panels of the top apart slightly to allow the main unit to slide clear a A Fixing Screws 5 12 Volt Connector IDC Coririector 5 Volt Cable DC Output Connector Mains Input a BEGAN Mains Fuse ca Mains Auxiltiary Output Disc Orive Dat
53. re are 14 MA lines 1 RA lines from ar 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 28 Issue 1 Master Series Compact Microcomputer 0 and logic look for short voltage levels ted tracks Check that all are getting through to the CRTC MUX 2 Check VSYNC pin 40 3 Check HSYNC pin 39 4 Check that CSYNC IC10 pin 10 and also at pin 4 5 6 6 1 4 There is a cursor stuck at the top left corner of the screen Check all co particular monitor is probabl If the RGB display alone is n LES 4 1C34 This This line shoul Service Manual line shoul If not then first replace the 6845 then IC46 d pulse low every 20ms d pulse low every 64us of SK9 ot working then y incorrect Check all video connections nothing else IC EE32 fault 33 the RGI both HSYNC and VSYNC superimposed B connector Alter PL10 6 1 5 The screen says ACORN MOS ACORN ADFS but nol Try typing CTRL E and put a formatted thing else BREAK configure nodir RETURN Turn the power o 3 The configura zero 6 1 6 BAS Check that the State If it is VIA IC25 6 1 7 The BAS 1 Ch
54. red in the measurement of HSYNC period Does it only occur on one of the video outputs 1 Is the CSYNC polarity link PL10 correct for your monitor 2 If it only occurs on composite video check that all the resistors R51 to R54 inclusive to the output transistors are correct in accordance with the circuit diagram Do they all have good signals going into them 6 3 3 There is no colour on RGB 1 Check the RGB connections out of the VIDPROC IC16 pins 14 12 and 10 2 If the fault is only in mode 7 or 135 then check RGB connections from SAA5050 IC15 pins 24 23 and 22 to the VIDPROC IC16 pins 13 11 and 9 6 3 4 The screen displays the wrong colours Check 1 and 2 above 6 3 5 The display works in all modes except 7 and 135 These modes work very differently from the others using IC15 the SAA5050 There are a number of faults which only exhibit themselves in these modes 1 There is a cursor which can be moved but no text Check the 6MHz input to the SAA5050 IC15 pin 19 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 1020 and 1021 2 The text is at all fragmented Check as above 32 Issue 1 Master Series Compact Microcomputer Service Manual 3 Not all colours are prese
55. rews and the the case lower it should be replaced The loudspeaker should be connected to PL1 from the case upper it should be remounted using the six screws previously removed Replace the cas the keyboard connector Reconnect the keyboard to the main PCB by pushing the connector onto the pins Ensure that all the pins are correctly engaged upper on the lower part ensuring that you do not trap and replace the four fixing screws 8 Issue 1 and gently lift the circuit board Master Series Compact Microcomputer Service Manual 4 Selection links and test points Link positions The following link positions can be set to alter vario the compu PL7 to the CRTC ter If fitted this allows the light pen strobe Factory position NOT F IC or copper wire PL9 reguired fit three pi If set No video output will be cut circuit board track and select th rel ns it two pins and use a mini shunt the video output will be normal inverted us actions inside LPTSTB to be connected if reguired with tinned Fit TT ED If set South the NORTH If change is and either use tinned copper wire or Factory position PL10 position either use t position usi PL11 connector adjusted as PL12 set South NORTH a mini shunt If set will be non i
56. rocomputer 7 Issue 1 Master Series Compact Microcomputer 3 Disassembly and assembly To service the X To disassemble Undo the four fixing screws under th part containing the keyboard B from the computer the power supply to the computer Service Manual BC Master Series Compact Microcomputer first disconnect and remove all peripheral connections case of the main unit Lift the top E carefully from the back The keyboard connector may now be removed from the printed circuit board by gently rocking the connector on the pcb to the left and the right The keyboard unit may itself b by undoing the six mounting screws removed from the upper part of the case The speaker may be disconnected from the main pcb by removing the connector from PL1 To remove the main printed circuit board undo the five fixing screws remove th xpansion connector cover from the left or West mounting area To reassemble If it is necessary to remov end th speaker lift it straight out of its Replace the main printed circuit board by putting the right hand edge with expansion connector in first and pushing it gently until the board drops into th cas lower expansion connector cover Replac If the speaker has been removed from by gently pushing it home If the keyboard has been removed the five PCB fixing sc
57. s 3 ICs plugged into their sockets correctly 4 power supply working and reaching the components concerned 5 all digital signals are either at clean TTL logic levels greater than 2 4V for 1 less than 5V for 0 or clean CMOS logic levels greater than 3V for 1 less than 1V for 0 On timed signals this must be true for the period 150ns before phi2 on read cycles and 300ns before phi2 on write cycles Hints for repair 1 Never solder to a computer which is switched on 2 Remove all user ROMs before starting Remember to put them back afterwards 3 Use sharp pointed meter probes to push through solder resist This will make finding short open circuits more reliable 4 Always suspect connectors 5 If you find a recurrent fault e g more than 10 machines let us know at ACORN so that we can include it in this manual if appropriate 25 Issue 1 Master Series Compact Microcomputer The following items of teat equipment are required for fault finding A set of screwdrivers Pliers Cut Mul ters timeter Logic probe 5 ohm 5W resistor The repair will be quicker with 100MHz dual beam oscilloscope Good qualit Spare monitor ty scope probes Spare disc drive Frequen A known Note around other to help pen circuits O O a S the system cy counter good computer to use as a signal model
58. s the 8MHz input to the 1772 correct Check that it is available at pin 18 If not then trace it back to 1C19 pin 8 and Is the 1772 DRQ line IC6 pin 27 32us when then disc interface has been asked to read catalogue If not then check that th ground and is connected to the IO Controller Check that the DRQ transitions IC6 pin 27 the NMI pin on the CPU IC28 pin 6 Check that the 1772 INTRO output 1C6 pin 28 pulse at them has line termination resistors Is the disc format Is the Read Data input to the attempt to read the disc necessary check that data is getting on 1772 IC6 pin 19 Service Manual then check the outputs on the 10 If these signals are not is fitted and is selected ted and correctly installed in the disc drive oscillating when you the end of ev If not then check on the 1772 disc inputs fitted a the signal cable and if to it from the disc drive nd IC6 IC16 pin 7 normally low but going high once every say a is line is not shorted to power or IC22 pin 5 appear logically inverted at produces a high going Cannot be changed As 1 2 above ery command issued to the 1772 If the INTRO line in t catalogue can be read but not the data is shorted high it will cause the 10 Controller to hold the CPU NMI line low thus masking
59. se engaged upon service work for or on behalf of ACORN Computers WARNING DANGEROUS VOLTAGES EXIST INSIDE THE CASE OF THE MONITOR STAND QUALIFIED PERSONNEL ONLY SHOULD ATTEMPT TO REPLACE PARTS COMPONENTS IN THE MONITOR STAND ENCLOSURE S IMPORTANT THE MONITOR STAND MUST BE EARTHED These instructions will be subject to change from time to time no responsibility can be accepted for any errors and or omissions ACORN COMPUTERS Ltd can accept no responsibility for any loss or damage resulting from use of the information contained herein this does not affect your statutory rights in any way The Disc Upgrade kit should include the following items 4 Drive Support Pillars Double Drive Data Cable 3 5 DS Disc Drive 4 M3 Pan Head Screws 8 M3 Shakeproof Washers 12 Month Guarantee Card Fitting Instructions Monitor Stand 56 Issue 1 Dismantling The Monitor Stand Turn the Mains switch to the OFF 0 position and unplug the mains lead from the mains wall socket and then from the mains socket on the Monitor Stand Remove the 5 Volt lead from the Keyboard Processor unit Also disconnect the Disc Drive Data cable from the Keyboard Processor unit DO NOT DISMANTLE THE MONITOR STAND WITH THE MAINS LEAD PLUGGED IN WITH THE MAINS SWITCH IN THE O OFF POSITION THERE ARE STILL DANGEROUS VOLTAGES PRESENT wi E unit Once th Monitor Stand t of the unit facing towards y
60. self will be due to a memory system failure These ar rarely due to the RAM chips themselves as these are usually very reliable Check the following very carefully 2 Check all connections from the CPU address bus 1C28 pins 9 to 20 and pins 22 to 25 inclusive to the DRAM address multiplexers ICs 37 39 and 40 see circuit diagram for pin numbers Then check the voltage levels of these signals at the multiplexer input pins All signals should have good CMOS levels less than 1V for 0 greater than 3V for 1 A constant 0 or 5V level implies a short to the relevant power rail Poor logic levels imply shorting to another logic signal 3 Check that the address at the DRAM inputs is stable for at least 15ns after RAS goes low and changes no later than 50ns after that edge see figure 8 This should occur once for every active high period of the system 2MHz clock out of the VIDPROC and once for every active low period 4 Check that the noise around logic LOW signals is generally less than 30 Issue 1 Master Series Compact Microcomputer 500mV If it is not 5 Check that the data bus is properly connected betw DRAMs 6 1 10 You can type but Service Manual then some signals may be shorting or a decoupling capacitor may be missing get two or more copies around the screen 1 Check IC34 pins 4 13 and 35 38 the CRTC scanning outputs circuit diagram
61. t points TP1 and TP2 are positioned close to ve output uld be between ve output If the seria interface is fitted the voltage on If the serial 10v and 5v A figure of 9v is quite typical Fas interface is fitted the voltage on A figure of v is quite typical ICH North of the PCB Issue l 1 Master Series Compact Microcomputer Service Manual TP3 connected to the CPU NOT NMI pin This should be generally At 5v while running making excursions to Ov only when disc and Econet are being used TP4 connected to the CPU NOT IRQ pin Check that this is not stuck either high or low when free running TP5 connected to the CPU SYNC pin This is asserted during an op code fetch by the processor and is used by ACCON to ensure that the correct memory area is accessed at this time If this is continuously high or low then the processor has completely stalled TP6 This is connected to the processor READ NOT WRITE line This should change between Ov and 5v frequently but not necessarily regularly Test points TP3 to TP6 are situated South of the CPU 1028 65C12 to the southeast of the PCB 1C Issue I Master Series Compact Microcomputer Service Manual 5 Hardware description 5 1 Introduction The Master Series Compact Microcomputer consists of a central processi
62. the remote computer 3 Is the cable properly connected Note this connector CAN be inserted the wrong way up 4Are all the cable connections correct i e no open short circuits 5 Are the device select connections to the SERPROC IC14 and ACIA IC13 from the IO controller correct 1C22 pin 34 and pin 36 respectively with no short circuits to either power supply rail 33 Issue 1 Master Series Compact Microcomputer Service Manual Is the SI GI RPROC getting a 1 23MHz timing reference IC14 pin25 If it is not check that it is available at 109 pin 11 and if not check that 16MHz is available at 9 pin 2 If the 16MHz is available try replacing IC9 74ALS169 counter socketed as it is part of the serial upgrade 7 Are either CTS IC14 pin 20 or RTS 1C14 pin 23 stuck high or low 8 Are the voltages at the test points TP1 and TP2 within the correct da 3 4 voltage range If not check the power supply to the MAX232 IC and try a replacement IC if the power supply is OK If all else fails check all remaining connections to the ACIA and SERPROC 5 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 Check 4 and 7 as above Check that data going into the lin
63. underside of the unit To hold the Data Cable in place plug in the IDC connector to Drive 0 the existing Disc Drive Note that the IDC connector is polarised and will only fit onto the Drive the correct way round therefore it should not be forced onto the connector Monitor Stand 59 Issue l Before fitting the new Disc Drive it has to be configured as Drive 1 so that the computer recognises it Do this by positioning the switch on the side of the drive as shown in figure 4 below If the drive type you are fitting is not the same as the one described her SONY F6 3W then refer to the Drive setting instructions in the Acorn Dealer Information Manual Disc Drive Drive Switch Pillar Positions Drive O Drive 1 FIGURE 4 Take the new Disc Drive and fit the support pillars and washers provided n the the upgrade kit onto it Take care not to over tighten them it the second disc drive in place ensuring the power cable isn t trapped ehind one of the support pillars Holding the Disc Drive and case turn he unit onto its side and align the holes on the case with the threads on he pillars Insert the screws with shakeproof washers into the pillars nd tighten firmly Turn the unit back onto its base and connect the ower and Data cables to drive 1 The Disc drive you have just installed n the unit O t H RD pot ct Re assembl
64. unit and unscrew the four support pillars from the to the new drive taking care not to ng the new Drive it has to be configured as Drive 0 so that the computer recognises it Do this by positioning the drive type you are fitting i the switch on the side of the Drive as shown in figure 6 below Note If s not as described here SONY F6 3W then refer to the Drive Setting instructions in the Acorn Dealer Information Manual Disc Drive Pillar Drive Switch Positions Drive 0 Drive 1 Figure 6 Replace the fixing screws and washers in the base of the Monitor stand fixing the new Drive in place Re connect the 5 12 Volt power connector and the Data Cable IDC connector Re assemble the unit by reversing the dismantling procedure described above Note ensure that when t he top Case is re fitted the ventilation slots are at the back of the unit A full functional test of the equipment should be carried out including the safety tests described at the beginning of this section before returning the equipment to the customer Monitor Stand bib Issue 1 SECTION 2 DISC UPGRADE INSTRUCTIONS Introduction These instructions are intended to provide information for service engineers and ACORN dealers who will be servicing the Master Compact Computer No part of these instructions are to be copied or communicated to persons other than tho

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