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Acorn computer A3000 Servicing

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Summary of Contents for Acorn computer A3000

  • Page 1 Servicing Module Archimedes & A3000 Servicing...
  • Page 2 Contents This module describes module-level servicing on Archimedes and A3000 computers. It covers routine maintenance of the computer and its peripherals, and fault-finding techniques for when the machine breaks down.
  • Page 3 A3000 The A3000 also comes in two pieces, a lid and a tray. Here, the lid should just lift off the tray beneath. Begin by removing the two metal clamps which secure the prongs from the lid at the back of the machine, and undo the screw in the centre of the bottom of the machine.

  • Page 4: Routine Maintenance

    RTC chip for at least 15 minutes without the batteries being present. The A3000 is fitted with a nickel-cadmium (NiCad) battery which is recharged when the machine is turned on and hence doesn't need replacing.
  • Page 5 Module Level Servicing Module level servicing involves fixing computers by swapping modules (PCBs, PSUs, etc.) rather than replacing defective components. This has a number of benefits for the technician: The fault-finding process is very much simpler and quicker than at component level.
  • Page 6 Main PCB: four major variants: A3000, A305/310, A440, A4x0/1 Floppy disk drive: 3.5" 800k (standard density). Two variants: a Sony drive fitted to A305/310 and A440 machines and a Citizen drive fitted to A3000 and A4x0/1. Keyboard: a 103-key IBM AT-style keyboard. Two variants: a membrane keyboard for A3000 machines and a conductive rubber pad keyboard for Archimedes.

  • Page 7: The Power Supply

    A3000 PSU The A3000 PSU delivers a single rail of +5V. It is enclosed in a cardboard cover. It has no mains outlet. To remove, free the cardboard cover at the PCB side of the PSU to reveal the PSU itself.
  • Page 8 A3000 The A3000 PCB is the first one from Acorn to use SMT (surface mount technology.) The four custom chips are soldered directly to the top side of the board, rather than being socketed in conventional PTH (pin through hole) sockets. All of the other components on the board, with the exception of some passives (resistors and capacitors) are mounted conventionally.

  • Page 9: Serial Port

    As a guide, 1200 baud will work fine, but 9600 will not. Line levels (not A3000.) The serial port on Archimedes drives the line with +/5V levels, to the RS423 specification. This will drive most RS232 peripherals, although the RS232 spec.

  • Page 10: Parallel Port

    Analogue RGB The Analogue RGB output is susceptible to static damage (A305/A310/A440 only.) This results in the early demise of VIDC, and is a component level repair. A3000 and A4x0/1 have static protection diodes added which cure the problem. Sound A305/A310/A440 machines may produce excess background noise through their internal speaker.

  • Page 11: Floppy Disk Drive

    No earth. If the drive is not earthed properly (i.e. not screwed down), it will again produce 'drive empty' errors. Citizen drives (A3000/A4x0/1) The Citizen drives fitted in modern machines cure the above problems, by having their own front panel (no alignment problems) and disk eject button. They do have a couple of quirks of their own: Problems when more than one drive fitted.
  • Page 12 A3000 Keyboard The A3000 keyboard is an integral part of the machine, and hence does not have a lead to break. Instead, the membranes connect directly to the A3000 PCB. Use a little care when removing these, as they are fragile: hold the white reinforcing strip and pull evenly and gently.
  • Page 13 Plug failure. The mouse lead, like the keyboard lead, is terminated in a mini DIN plug. Plugging a mouse into an A3000 is a tricky job, and again needs to be handled with care if the plug is not to be damaged. The cure is, again, to fit a new plug.
  • Page 14 Monitor and lead The standard colour monitors supplied with Archimedes systems are rebadged Philips CM8832s. Acorn provides no support for servicing these monitors - no manuals, no spares - and so servicing must be carried out by a Philips service centre, such as Granada Microcare. The monitors seem quite reliable, with the only noteworthy weakness being in the vertical scanning circuitry, which can fail to scan.
  • Page 15 Fault Finding Hints The first thing to do when presented with a faulty machine is to reset its CMOS RAM: hold down the 'Delete' key on the keyboard while turning the machine on. Keep it pressed for a couple of seconds after power-on, to give the machine time to come out of reset and see it.
  • Page 16 Field Change Orders (FCOs) There follow a set of FCOs (Field Change Orders) for Archimedes machines. Most of them refer to the older machines (A305/A310/A440.) They should give an idea of the faults which have been found frequently on Archimedes, and the repairs which are necessary to cure them.
  • Page 17 FCOE008 (A305/A310/A440) FCO E008 - Fix to cure excessive background noise DESCRIPTION Acoustic pick-up causing hum from the internal loudspeaker is reduced. Please note that the noise on earlier computers when 'BREAK' or `ESCAPE' is pressed is due to a software problem with earlier versions of Arthur, and will be cured when Arthur 1.2 is fitted.
  • Page 18 FCOE009 (A305/A31 0/A440) FCO E009 - Fix to cure problems with some monitors DESCRIPTION RGB output levels are too low to drive some monitors. Also sync on green is no longer required. This modification need only be carried out at the request of the customer.

  • Page 19: Second Method

    FCOE009 (contd.) SECOND METHOD: Remove the circuit board from the main unit. Cut the leads to resistors R39, R20, R41 and R59, leaving enough of the lead on the board to allow new resistor leads to be soldered to the existing leads except on R39. The leads on R39 may be cut right back to the circuit board.
  • Page 20 FCO E011 (A305/A310/A440) FCO E011 - Fix to Reduce Video Noise DESCRIPTION Breakthrough of system noise occurs onto the screen. This shows as rippling on screen, and is particularly noticeable with colour monitors. This seems particularly prevalent when running 'ArcWriter'. INSTRUCTION Remove the circuit board from the computer.
  • Page 21 FCO2000 FCO 2000 - Improvements to Winchester Circuitry on A440 DESCRIPTION This deviation improves the performance of the Winchester circuitry, removing the problem of intermittent lock failure of the phase locked loop which would be visible to the user as excessive re-reads. This would particularly show up as soft errors on verify.
  • Page 22 FCO2000 (contd.) The components used are available from Farnell, the following part numbers are suitable: 8k2 resistor BTF48K2 1 n2 capacitor 146-460 1N4148 diode 1N4148 47pF capacitor 146-485 22k resistor BTF422K...
  • Page 23 FCO2002 (A305/A31 0/A440) DESCRIPTION Timing problems with printer control lines have led to spurious operation of some printers. This has proved particularly noticable when using Integrex colour printers in graphic mode while line feeding • a spurious line feed being generated. INSTRUCTION 1.
  • Page 24 FCO2003 DESCRIPTION Some G65SC51 ICs fitted to Archimedes computers may exhibit certain problems relating to Serial I/O. More recent production of these ICs have been screened to ensure that this problem does not occur. INSTRUCTION 1. Identify IC9 inside the computer. If it is marked CMDG65SC51 with a date code of 8801 (1988 week 1) or later then this computer does not meet modification.

  • Page 25: Reason For Issue

    FCO2007 (A4x0/1) Field Change Order No. 2007 Date of Issue 27th July 1989 Applicable to (product) Archimedes 400/1 series. Model 410/1 REASON FOR ISSUE When upgrading above unit with second floppy disc drive incorrect LED operation may be observed. i.e. LED lit when drive not selected. TYPES AFFECTED (eg serial no/issue/level) 27 - AKB40 - 1000001...

  • Page 26: Special Instructions

    FCO2007 (contd.) SPECIAL INSTRUCTIONS:- All products in manufacture after serial No. 1002500 will not exhibit problems. ARCHIMEDES A410/1 COMPUTER - CITIZEN FLOPPY DISC DRIVE MODIFICATION WHEN FITTING SECOND FLOPPY DISC DRIVE DEALER UPGRADE A problem has been identified when a second Floppy Disc Drive upgrade is fitted to within the Archimedes 410/1 computer.
  • Page 27 FCO 2007 (contd.) 5. Carefully slide the disc drive bracket and the floppy drive assembly towards the rear of the unit. Turn the drive over to check if component number R61 is fitted. This device is located adjacent to the MOD rev box. If R61 is fitted, proceed to No.6.
  • Page 28 FCO 2007(contd.) 13.The original disc drive should be suitably packed and returned to the Acorn Spares and Warranty Department, Fulbourn Road, Cherry Hinton, Cambridge, with a fully completed Service Report. A replacement unit will be sent to you to replenish your stock. Distributor dealers should return the exchanged drive to their distributor for action - not to Acorn direct.

  • Page 29: Description Of Change

    FCO2008 F I E L D C H A N G E O R D E R Acorn Computers Ltd Field Change Order No. 2008 Date of Issue 6th September 1989 Applicable to (Product) A310 (AKB15), A440 (AKB20) REASON FOR ISSUE The FPU (AKA20) and SCSI (AKA30) expansion cards required the host machine to contain a MEMC1 A (as opposed to MEMC1).

  • Page 30: Parts Required

    To upgrade existing machines to include a MEMC1A memory controller. This is a necessary upgrade before fitting Acorn SCSI and (440 only) Floating Point expansion cards, and also increases performance generally by about 10%. This modification is not required on Archimedes 400/1 series, Acorn R140 or A3000 systems. PARTS REQUIRED...
  • Page 31 FCO 2008 (contd.) PCB MODIFICATION PROCEDURES WARNING: TAKE ALL PRECAUTIONS REGARDING STATIC ELECTRICITY AND EARTHING IN ACCORDANCE WITH BS 5783 ARCHIMEDES 440 ONLY 1. Switch off and disconnect the computer from the mains supply 2. Remove the top cover and the backplane (if fitted) disconnect the power leads, and remove the main PCB, in accordance with the disassembly instructions given in the service manual.
  • Page 32 FCO 2008 (contd.) 8. Remove existing PAL from position IC44, and replace with a new MEMC1 A PAL ( part number 0277,401). 9. Reassemble the computer. 10 Test 11 Complete the 'Installation details' on the Upgrade Guarantee form (part number 0476,363). ARCHIMEDES 310 Follow steps 1-2 and 7-11 only of the 440 modification procedure detailed above.

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