British Broadcasting Corporation Master Series Microcomputer Service Manual British Broadcasting Corporation Master Series Microcomputer Service Manual Part No 0443,004 Issue 1 April 1986 M S S M W BBC ' B B C. C A C L 1986 N the whole or any part of the information contained , or the product described , this manual may be adapted or reproduced in any material form except with the prior written approval of A C L (A C). T product described in this manual and products for use with , are subject to continuous development and . A information of a technical nature and particulars of the product and its use ( including the information and particulars in this ) are given by A C in good . H, it is acknowledged that there may be errors or omissions in this . A list of details of any amendments or revisions to this manual can be obtained upon request from A C T E. A C welcome . A :- T E A C L N R C CB5 8PD A maintenance and service on the product must be carried out by A C authorised . A C can accept no liability whatsoever for any loss or damage caused by service or maintenance by unauthorised . T manual is intended only to assist the reader in the use of this , and therefore A C shall not be liable for any loss or damage whatsoever arising from the use of any information or particulars , or any error or omission , this , or any incorrect use of the . T A C . F 1986 P A C L 1 I 1 M S S M WARNING: THE COMPUTER MUST BE EARTHED IMPORTANT: T : G Y E B N B L T moulded plug must be used with the fuse and fuse carrier firmly in . T fuse carrier is of the same basic colour ( not necessarily the same shade of that ) as the coloured insert in the base of the . D manufacturers' plugs and fuse carriers are not . I the event of loss of the fuse , the moulded plug MUST NOT be . E replace the moulded plug with another conventional plug wired as detailed , or obtain a replacement fuse carrier from an authorised A . I the event of the fuse blowing it should be , after , 3 ASTA BS1362. I the socket outlet available is not suitable for the plug , the plug should be cut off and the appropriate plug fitted and wired as previously . T moulded plug which was cut off must be disposed of as it would be a potential shock hazard if it were to be plugged in with the cut . A , : T wire which is coloured green and yellow must be connected to the terminal in the plug which is marked by the letter E, or by the safety earth symbol - I-, . T N, . T L, . 2 I 1 Master Series Service Manual BBC Master Series Microcomputer Service Manual Contents 1 - I 2 - Packaging and installation 3 - Disassembly and assembly 4 - Selection links 5 - Hardware description 5.1 I 5.2 C 5.3 I I/O 5.4 E I/O 6 - Test equipment 7 - Fault finding 7.1 S 7.2 S RAM 7.3 V 7.4 R 7.5 A 7.6 RS423 7.7 C 7.8 D 7.9 P 7.10 U 7.11 1MH 7.12 T T 7.13 I - 7.14 S 7.15 M 7.16 C 7.17 E Appendix C P C PCB F EPROM E K 3 I 1 M S S M 1 Introduction T manual is intended to provide the information required to diagnose and repair faults on the BBC M S M A C L C, E. T information contained in this manual is aimed at service engineers and A dealers who will be servicing the BBC M S M A C L. 4 I 1 M S S M 2 Packaging and installation T microcomputer is supplied with - moulded polystyrene packing in a cardboard . S with the microcomputer is a W G, an aerial , a welcome , a welcome , two reversible keyboard , a VIEW reference , a VS , . T mains supply for UK models is 240V AC 50H. T microcomputer is supplied with a moulded 13 amp square pin . I this plug is unsuitable then it must be cut off and thrown . I for fitting a replacement plug are given right at the front of this . T . D not use the microcomputer in conditions of extreme , , humidity or dust or in places subject to . D not block ventilation under or behind the . E that no foreign . 5 I 1 Master Series Service Manual 3 Disassembly and assembly T service the BBC M S M, first disconnect the power supply plug from the mains and remove all peripheral connections . To disassemble T lid of the microcomputer case may be removed after undoing the four fixing screws underneath the . DO NOT remove the lid with the . I -: keyboard ( ) T remove the , first unplug the 2 keyboard connectors from the main printed circuit . U the 3 screws holding the keyboard to the case , and the 1 screw which holds it to the power supply . T , . T power supply unit is connected to the main circuit board by seven - connectors which must be . T screws on the underside of the case are undone allowing the unit to be . O , (M36). T main printed circuit board is removed complete with the metal -. T remove the main printed circuit , undo the 4 fixing screws which pass through the cartridge connectors into the case , and the 1 screw which holds the metal - to the power supply . R the circuit board from the case by lifting . To reassemble R the main printed circuit board by putting the front edge ( connector ) in first and pulling it forwards until the metal - drops . M sure that all the lugs on the lower case locate with all the correct points on the PCB and -. R the 4 PCB fixing screws which pass through the cartridge , and the single screw which joins the - to the power supply . R the power , being careful to route the wires , and connect the wires () to the - connectors on the PCB, . PCB +5V () PCB OV (). T -5V (). 6 I 1 M S S M R the speaker and battery , first plugging the two connectors into their correct positions on the , the battery connector to PL8 either way , and the speaker connector to PL9 either way . N that although the battery connector can be plugged either way , it must locate on all three pins or the . C . R the . R the 4 , 3 to the lower case and 1 to the power supply . B careful to reconnect the keyboard ribbon sockets so that all the pins are ; it is easy to displace the . M one final check that all reconnections have been made , especially the power supplies which will short circuit if any two are . R , . 7 I 1 M S S M 4 S LK1 PCB , A: 1MH B A I/O 2 . I -A 1MH B . I B 1MH B (M 1 ). T A . T B . LK2 PCB , : C -5V . O . I some , particular cartridge hardware may need a -5V supply that is decoupled from the main computer -5V . T do this R9 needs to be fitted and LK2 which is a track on the circuit board should be . LK3 : N . LK4 , : C IRQ. O . T 6818 /RAM chip has a daily alarm function built . W the alarm is , the CPU is interrupted via its IRQ . R the shunt from LK4 disconnects the CPU IRQ line to the clock . T function is not supported by the operating system as this feature may not be present in future versions of the circuit . C the clock chip must be directly operated by the . LK5 PCB , E: CSYNC . T . T polarity of the composite synchronisation signal is determined by this . I is supplied as a track on the PCB causing negative synchronisation . T track must be broken and a piece of wire used to make the other side of the link for positive . 8 I 1 M S S M LK6(0) LK6(1) , A B: M C S. M- . T 4 : L A B - T 16MH - . T . L between B and D - T computer main 16 MH reference must be provided from pin A17 on either of the cartridge . N that in this case a clock source MUST be provided or the dynamic memories . L between C and D - T cartridges are clocked by the 8 MH signal from the . T is a synchronous signal with the 2 MH (2) , also supplied to the . N that the link between A B . LK7 PCB , E: V . T . T polarity of the video RGB signals is determined by this . I is supplied as a track on the bottom of the PCB causing true . T track must be broken and a piece of wire used to make the link W . LK8 : N . LK9 : N . LK10 NTSC : C S. T . W used with NTSC VHF , the modulator enables one of two channels to be . N that the computer as supplied for use in UK UHF LK10 . LK11 : N . LK12 P, B (E): CSYNC/C M D. T . P A - T CSYNC GENLOCK . P B - C hardware cartridges may need to detect whether they are plugged into a M S computer or an A E. M computers are shipped with this link in the B , causing a logic LOW to appear on pin A10 of the . T E has no . 9 I 1 M S S M LK13 PCB , W: A D .