Acorn BBC Master 128 Service Manual Download Page 76

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Summary of Contents for BBC Master 128

Page 1: ...BBC Master 128 SERVICE MANUAL 1985 Acorn...

Page 2: ...British Broadcasting Corporation Master Series Microcomputer Service Manual...

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Page 4: ...British Broadcasting Corporation Master Series Microcomputer Service Manual Part No 0443 004 Issue 1 April 1986...

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Page 6: ...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...

Page 7: ...eplaced 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...

Page 8: ...7 1 Switch on 7 2 Sideways RAM 7 3 Video 7 4 Real time clock 7 5 Analogue port 7 6 RS423 port 7 7 Cassette interface 7 8 Disc drive interface 7 9 Parallel printer port 7 10 User port 7 11 1MHz bus 7 1...

Page 9: ...se 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 service engineers and Ac...

Page 10: ...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...

Page 11: ...it 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 u...

Page 12: ...on all three pins or the polarity will be wrong Check carefully Replace the keyboard Replace the 4 screws 3 to the lower case and 1 to the power supply unit Be careful to reconnect the keyboard ribbo...

Page 13: ...on the circuit board should be cut LK3 Not present LK4 plug made Clock chip IRQ One position link The 6818 clock RAM chip has a daily alarm function built in When the alarm is triggered the CPU is int...

Page 14: ...nk The polarity of the video RGB signals is determined by this link It is supplied as a track on the bottom of the PCB causing true polarity This track must be broken and a piece of wire used to make...

Page 15: ...AL NTSC select Two position link As shipped in the UK this link is a track on the bottom of the PCB causing the CHROMA chip to encode colour information on to the television output in PAL format If th...

Page 16: ...a 32Kbyte ROM occupying slots 4 and 5 may be plugged into socket labelled IC37 LK20 Not present LK21 plug not made Light Pen Strobe to cartridge This link is not normally made so position B10 on the...

Page 17: ...ns 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 I O Various I O devices operate solely within the confines...

Page 18: ...ted 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...

Page 19: ...rcuit 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 c...

Page 20: ...tc 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 socket...

Page 21: ...ermit 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 be e...

Page 22: ...er 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 The contents of ROMSEL determine the pagin...

Page 23: ...g 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 ROMS...

Page 24: ...rd 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...

Page 25: ...ad The matrix is as follows Figure 5 Sound Generator The sound generator is an SN7694A device Three sound channels plus one pseudo random noise channel are provided The full description of it is found...

Page 26: ...e 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 Thi...

Page 27: ...the chip but operating system support to this facility is not provided An optional nIRQ connection can be made to the CPU from the clock chip enabling the alarm to change program flow Operation of th...

Page 28: ...es at this speed the internal second processor TUBE Its data bus is connected directly to the CPU data bus The second processor interface will only be specified as a hardware data transfer definition...

Page 29: ...figure 7 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 hard...

Page 30: ...for the cursor to be adjusted to pixel accuracy Hardware Scroll Scrolling may be achieved in any mode by re programming the 6845 start of screen address to an integral number of video lines further d...

Page 31: ...es 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 soft...

Page 32: ...r 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 Thi...

Page 33: ...on the microcomputer disc printer user 1MHz bus TUBE UHF video ROB RS423 cassette A to D and sound output To use this tester the microcomputer must at least have the CPU running and the MOS BASIC ROM...

Page 34: ...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 f...

Page 35: ...vers Pliers Cutters 10A Multimeter RGB monitor logic probe 5 ohm 5W resistor The repair will be quicker with 100MHz dual beam oscilloscope Good quality scope probes TV composite monitor colour monitor...

Page 36: ...rts 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 i...

Page 37: ...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 cured should still be...

Page 38: ...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...

Page 39: ...ble at IC25 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 v...

Page 40: ...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 7 1 8 Not all keys work on the keyboard...

Page 41: ...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 AS IC11 pin 14 low DS IC11 pin 17 low 4 Check that R W IC11 pin 15 wiggl...

Page 42: ...at the data bus is properly connected between the CPU and the DRAMs 7 1 12 You can type but get two or more copies around the screen 1 Check Test Points TP7 to TP20 the CRTC scanning outputs shown on...

Page 43: ...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...

Page 44: ...k 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...

Page 45: ...ers appear unstable Check the components and signals around the 6MHz generator 1C39 and 1C25 7 Lines are broken up Check all connections to the PBC IC21 7 4 Real time clock 7 4 1 Gives strange charact...

Page 46: ...the chip select from the 10 controller IC15 pin 35 correctly connected to IC49 pin 23 8 Does IC49 have a 1MHz timing reference on pin 2 7 5 2 Gives erroneous results on just one channel 1 The plug an...

Page 47: ...e equivalent receive and transmit respectively 2 Check 3 6 and 7 as above 3 Check that data going into the line driver IC50 comes out of it The driver could be faulty otherwise 4 Check that the Tx CLK...

Page 48: ...en subsequently damaged 6 Check that the ACIA and SERPR0C have correct i e no open or short circuit connections on all pins 7 Check the 1 23MHz connection to the ACIA 8 As a last resort change the SER...

Page 49: ...in the right way round 4 Is the Read Data input to the 1770 1772 IC3 pin 19 wiggling when you attempt to read the disc If not then check the signal cable and if necessary check that data is getting on...

Page 50: ...ted 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...

Page 51: ...r printer if possible 5 Check that pin 40 on the User VIA IC6 has a pull up to 5V R11 but is not short circuited to 5V 6 Check that data appearing on Port A of the VIA IC6 pins 2 to 9 appears on the o...

Page 52: ...equipment 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 co...

Page 53: ...dance 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 The envelopes use memory shared with serial data buffer space 7 14 3 Prod...

Page 54: ...es bent or worn If so the connector must be replaced 7 17 Econet Econet can only be serviced properly by Econet service centres who will have the necessary test equipment to check the system thoroughl...

Page 55: ...Master Series Service Manual Appendix 50 Issue 1...

Page 56: ...ster 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 SK11 cassette 7 pin DIN 55 Issue...

Page 57: ...type 1 5V 9 light pen strobe notLPSTB 2 0V 10 digital switch input I1 3 0V 11 voltage reference VREF 4 CH3 12 CH2 5 analogue ground 13 digital switch input I0 6 0V 14 voltage reference VREF 7 CH1 15...

Page 58: ...6 notMOTOR 17 0V 18 notDIR 19 0V 20 notSTEP 21 0V 22 notW DATA 23 0V 24 notWR EN 25 0V 26 notTK0 27 0V 28 notWR PCT 29 0V 30 notR DATA 31 0V 32 notS SEL 5 1 4 33 0V 34 notRDY 8 PL3 printer 26 way IDC...

Page 59: ...3 0V 14 PB4 15 0V 16 PB5 17 0V 18 PB6 19 0V 20 PB7 PL5 1MHz bus 34 way IDC 1 0V 2 R notW 3 0V 4 1E 5 0V 6 notNMI 7 0V 8 notIRQ 9 0V 10 notPGFC 11 0V 12 notPGFD 13 0V 14 notRS 15 0V 16 audio in out see...

Page 60: ...2 R notW 3 0V 4 2E 5 0V 6 notIRQ 7 0V 8 notTUBE 9 0V 10 notRS 11 0V 12 DO 13 0V 14 D1 15 0V 16 D2 17 0V 18 D3 19 0V 20 D4 21 0V 22 D5 23 0V 24 D6 25 0V 26 D7 27 0V 28 AO 29 0V 30 Al 31 5V 32 A2 33 5V...

Page 61: ...PL24 keyboard 2x15 pin molex PL11 1 C6 2 BAT 3 R0 4 R6 5 R7 6 R2 7 R1 8 C11 9 C10 10 C12 11 C0 12 C2 13 c9 14 c4 15 C5 PL24 1 C8 2 C7 3 C3 4 C1 5 R5 6 R4 7 R3 8 C 9 SHIFT LOCK 10 CAPS LOCK 11 POWER 12...

Page 62: ...19 20 21 22 23 0502 100 RES 10R C MF 5 0W25 4 R27 37 38 113 24 0502 101 RES 100R C MF 5 0W25 4 R48 49 57 58 25 0502 102 RES 1K0 C MF 5 0W25 17 R13 33 34 43 47 51 54 56 75 117 122 133 137 145 148 150...

Page 63: ...128 129 61 62 0502 473 RES 47K C MF 5 0W25 1 R115 63 64 0502 562 RES 5K6 C MF 5 0W25 1 R74 65 0502 563 RES 56K C MF 5 0W25 1 R82 66 0502 565 RES 5M6 C MF 5 W25 1 R17 67 68 0502 680 RES 68R C MF 5 0W25...

Page 64: ...119 0699 001 CPCTR TRMR 2 22p 5V 1 VC1 120 0699 004 CPCTR TRMR 5 5 40p 25V 1 VC2 121 0701 770 IC WD1770 FDC 5 25 1 IC3 122 0704 105 IC 4464 DRAM 120nS 64Kx4 4 IC17 18 23 26 123 0705 050 IC SAA5050 CHT...

Page 65: ...73 0780 309 TRANS BC309 PNP 2 Q11 13 174 175 0794 148 DIODE SI 1N4148 14 D7 10 12 13 17 24 176 177 0800 001 CONR 5W SKT DIN RA DOM 1 SK10 178 0800 002 CONR 6W SKT DIN RA PCB 1 SK9 179 0800 003 CONR 7W...

Page 66: ...CONR BNC SKT 75R PNL 1 SK8 218 0800 611 CONR PHONO SKT RA PCB 1 SK13 219 0801 200 CONR 20W 0 1 SR ZIF 4WR 1 PL12 220 221 0810 001 RLY 1P CO 5V 50R PCB 1 RL1 222 223 224 225 226 227 0820 160 XTAL 16 00...

Page 67: ...nsistors on the circuit diagram given later in the Appendix The circuit diagram is split into 2 sheets and the sheet on which the component appears is given in the Sheet column The Position column giv...

Page 68: ...17 6 0 1 18 4 0 1 19 9 4 3 5 6 6 0 8 0 9 1 20 3 8 1 21 9 3 9 4 1 22 7 1 2 23 5 o 1 24 3 8 4 8 1 25 6 5 7 9 1 26 3 0 1 27 4 8 1 28 4 2 5 6 1 29 4 7 1 3o 4 5 1 31 4 4 1 32 7 3 1 33 4 6 1 34 2 1 6 2 7 9...

Page 69: ...7 2 12 5 8 2 13 4 4 2 14 3 9 2 15 5 7 2 16 17 5 7 2 18 5 6 2 19 5 5 2 20 4 4 2 21 3 9 2 22 2 4 2 23 6 9 2 24 5 7 2 25 5 6 2 26 4 4 2 27 4 5 2 28 4 4 2 29 6 8 2 30 5 6 2 31 5 4 2 32 6 5 2 33 3 3 1 34 3...

Page 70: ...5 60 6 4 6 5 1 61 62 6 7 1 63 64 6 2 1 65 3 8 1 66 7 5 2 67 3 3 1 68 7 8 1 69 7 6 2 70 4 3 2 71 7 6 2 72 7 6 2 73 7 6 2 74 7 5 2 75 7 8 1 76 7 7 2 77 7 7 1 78 7 7 1 79 80 8 7 2 81 8 6 2 82 9 9 2 83 8...

Page 71: ...6 2 115 5 2 2 116 5 2 2 117 5 2 2 118 8 8 1 119 120 6 4 2 121 5 3 1 122 1 0 1 123 124 125 3 0 1 126 2 0 1 127 3 1 1 128 5 8 1 129 6 8 1 130 8 7 1 131 8 7 1 132 8 7 1 133 8 7 1 134 8 7 1 135 136 8 7 1...

Page 72: ...5 4 2 10 4 3 2 11 5 7 2 12 5 5 2 13 2 3 1 14 6 5 2 15 5 4 2 16 5 3 2 17 5 5 2 18 5 3 2 19 1 9 1 20 9 4 1 21 0 4 1 22 0 8 1 23 5 5 1 24 5 5 1 25 5 4 1 26 6 6 1 27 28 29 30 6 5 1 31 32 7 7 2 33 34 7 6...

Page 73: ...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 1 2 68 9 0 2 69 9 0 2 70 9 2 2 71 9 1 2 72 9 1 2 73 9 0 2 74 75 9 4 2 76 9 4 2 77 5 3 2 78 3 7 1 79 6 4 2 80 5 4 1...

Page 74: ...6 6 4 2 7 5 5 2 8 6 8 2 9 7 2 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 8 5 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 1 7 2 2 5 8 2 3 6 8 2...

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