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Amstrad PC3086 Maintenance Guide

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Back panel of a Generation 3 system unit, with the voltage selector beside the mains inlet (user manual p. 3-7)

The Amstrad PC3086 shares its case, clock chip arrangement and start-up procedure with the Amstrad PC3286 and Amstrad PC3386SX, and one Amstrad user manual covers all three. The sections on safety, opening the case, the clock chip and head parking apply to all three models; the links, switches and drives described are the PC3086's. The 286 and 386SX main board, with its SIMMs and processor daughterboard, is covered in the Amstrad PC3286 Maintenance Guide. Amstrad's service manual for the range (reference SM-PC3000) has not been published online; the Centre for Computing History holds a paper copy.[1][2] Faults are in the Amstrad PC3086 Troubleshooting Guide.

Safety

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Warning: the power supply inside the system unit runs from the mains. Unplug the mains lead before removing the cover.

  • Amstrad's manual carries the warning "high voltage inside" and requires the machine to be earthed. A UK plug on the mains lead must have a 5 A fuse, not the 13 A fuse supplied.[3]
  • Check the voltage selector switch beside the mains inlet on the back panel before switching on: 200–240 V for the UK and Europe, 100–120 V for the United States and Canada. The power switch is at the bottom right of the front panel.[4]
  • The back panel has a power outlet for the monitor as well as the VGA socket.[5]
  • Once the cover is off, keep one hand on the metal cabinet to discharge static before touching the board.[6]

Opening the case

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The same method applies to all three Generation 3 models.[6][7]

  1. Switch off, unplug the mains lead and disconnect the keyboard, monitor and other cables.[8]
  2. Undo the screws along both side panels. John Elliott counts six, three each side, with sometimes a seventh at the centre of the back.[6][8]
  3. Facing the front, slide the lid towards you by about three inches (75 mm) only. Wires run from the inside of the front panel to the main board, and sliding the lid further pulls them off.[6]
  4. Lift the lid and rest it on the front panel. Elliott warns that the power button can catch on the case and snap off; leave the wires connected.[6][8]

Clock chip (CMOS RAM)

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Inside a PC3286, with the clock module at top left (photo: tarasque, CC BY 4.0)

The clock, the date and, on the PC3086, the floppy drive configuration are kept in a CMOS RAM chip that contains its own lithium battery. When the battery is exhausted the BIOS reports "WARNING: CMOS battery failed". Amstrad's instruction is to replace the complete chip, because the battery cannot be replaced or recharged, and warns that recharging it risks an explosion and that the old chip must not be put in a fire.[4][9][10] Elliott's replacement procedure for the PC3086:[8]

  1. Obtain a DS1287-compatible clock module. The original Dallas DS1287 is no longer made; Elliott used a DS12C887.
  2. Open the case as above.
  3. Find the clock chip on the left-hand side of the board, near the back. It is taller than the other chips, is marked DS1287 with a picture of a clock, and has a white dot at one corner. Note which end the dot is at.
  4. Lever the chip out of its socket with a small screwdriver at each end in turn, keeping the legs straight.
  5. Fit the new chip with its dot (which may be black) at the same end, every pin in its hole.
  6. Close the case and switch on. Expect a request to set the time and date, without the battery warning.
  7. Set the date, switch off, wait a few minutes and switch on again to check that the clock has kept the date.

On the PC3086 the floppy drive types are stored in the same chip, so set them again with the DEVICE command after fitting a new one (see Floppy drives).[4][11]

Video DIP switches

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The video DIP switches beside the VGA socket on a PC3286 (photo: tarasque, CC BY 4.0)

Four DIP switches on the back panel control the built-in Paradise VGA. The PC3086 uses switches 1 and 2 only. The factory setting is switch 1 off and switch 2 on.[12][13]

PC3086 video DIP switches
Switch On Off
1 Multi-frequency monitor attached Fixed-frequency VGA monitor (default)
2 PS/2 mode: automatic colour and monochrome switching (default) AT mode: switch with DEVICE DISPLAY; must be off if an MDA or Hercules card is fitted
3, 4 Reserved on the PC3086
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The PC3086 links are on the main board (drawing on p. 11-5 of the user manual). Amstrad marks several "do not change"; Elliott worked out their functions from the service manual schematic.[6][14]

PC3086 option links
Link Out (no jumper) In (jumper fitted)
LK1 Drive A has changeline (720 KB) Drive A has no changeline (360 KB)
LK2 Drive B has changeline (720 KB) Drive B has no changeline (360 KB)
LK3 Power-on self test enabled Self test skipped
LK4 Do not change; jumper on pins 2 and 3. Elliott reads pins 1 and 2 as reducing memory to 512 KB
LK5 Leave open. Elliott reads it as selecting a 32 KB BIOS ROM in place of 16 KB
LK6 Do not change; jumper on pins 1 and 2 (write precompensation 250 ns; pins 2 and 3 give 125 ns)
LK7 On-board COM1 enabled On-board COM1 disabled
LK8 On-board VGA enabled On-board VGA disabled
LK901, LK902 Primary display when the VGA is disabled: both out, EGA or VGA card; LK902 in, CGA 80 columns; LK901 in, CGA 40 columns; both in, MDA or Hercules
LK952 Hard disk I/O address: pins 1 and 2 primary, pins 2 and 3 secondary
LK953 Hard disk BIOS: no jumper, disabled; pins 2 and 3, primary; pins 1–2 and 3–4, secondary
LK954 Do not change (leave open)
LK955 Hard disk interrupt, from the schematic: pins 1 and 2 IRQ 5, pins 2 and 3 IRQ 2

LK951 is not in Amstrad's table; Elliott links it to the IDE reset line on the schematic.[14] The display links LK901 and LK902 are explained on p. 6-7 of the manual.[12]

Hard disk

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  • Before moving the machine, park the heads: type PARK at the C:\> prompt, wait for "The heads are parked - You may now switch off", and switch off within ten seconds, or press Esc to carry on working.[9]
  • Let the machine reach room temperature before using it after it has been somewhere cold, and handle the system unit gently, since the drive is sensitive to shock.[9]
  • The built-in adaptor is XT-type IDE. A replacement drive must support XT mode; a normal ATA drive will not work unless it has a jumper or switch for XT mode.[15][16]
  • To use a different controller in a slot, disable the built-in one by removing the jumper on LK953 and moving LK952 to pins 2 and 3, and use an XT-type controller with its own BIOS ROM.[16][15]

See Hard Drive Maintenance and Repair.

Floppy drives

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  • Drive types are held in the clock chip and set with DEVICE SETFD, which also sets changeline, A/B swapping and write precompensation. Change LK1 and LK2 to match the drives fitted.[11][6]
  • The controller supports high-density drives. The PC3086 cable has no twist, but it can be replaced with a standard twisted cable; Elliott ran a TEAC FD-235HF as drive A: this way, set as 1.44 MB with changeline. The drive light then stays on, because a standard twist swaps both the drive select and motor-on lines.[16]
  • Elliott suggests a floppy emulator such as a Gotek set up as a 720 KB drive as an alternative to an original drive.[17]

See Floppy Drive Repair.

Co-processor and memory

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  • An 8087 fits the empty 40-pin socket on the main board. No links or settings need changing.[7]
  • The 640 KB on the board cannot be increased; more memory needs an 8-bit ISA expanded memory card.[1]

Capacitors

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No capacitor values have been published for the PC3086's main board or power supply. Amstrad's service manual is not available online, and no community recap list exists. For the signs of failed electrolytics see Capacitor Failure Symptoms.[2][18]

Tools

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  • Cross-head screwdrivers and an anti-static strap
  • A small flat screwdriver or IC extractor for the clock chip
  • Digital multimeter
  • See Recommended Tools.
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References

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  1. ↑ 1.0 1.1 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 1-2 to 1-4. Specifications of the three models and memory configuration.
  2. ↑ 2.0 2.1 Centre for Computing History, "Amstrad PC3086 PC3286 PC3386SX Colour Personal Computers Service Manual" (CH27476): 53-page service manual with schematics and wiring diagrams, reference SM-PC3000. Retrieved 2026-10-02.
  3. ↑ Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), p. 1-6. Mains plug, 5 A fuse, earthing and the high-voltage warning.
  4. ↑ 4.0 4.1 4.2 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 3-7 to 3-15. Voltage selector, power switch, the "Please wait." self-test dots, start-up messages and BIOS versions, and the SETUP program for the PC3286 and PC3386SX.
  5. ↑ Amstrad plc, PC3086 leaflet, © August 1990, p. 2 (specification). Hosted as File:Amstrad PC3086 leaflet (1990).pdf.
  6. ↑ 7.0 7.1 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 7-1 to 7-7. Processor speeds, fitting an 8087, 80287 or 80387SX co-processor, and opening the system unit.
  7. ↑ 8.0 8.1 8.2 8.3 John Elliott, "PC3086 clock chip replacement", seasip.info, 15 June 2004. Retrieved 2026-10-02. The CMOS battery warning, the DS1287 and its DS12C887 substitute, case removal and chip location.
  8. ↑ 9.0 9.1 9.2 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 13-2 to 13-4. Transporting a hard disk PC, PARK.COM, and replacing the CMOS RAM.
  9. ↑ Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 14-1 to 14-3. Non-fatal and fatal hardware error messages.
  10. ↑ 11.0 11.1 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 4-2 to 4-18. The DEVICE command: display, floppy drive, cache, memory map and processor speed settings.
  11. ↑ 12.0 12.1 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 6-5 to 6-15. PS/2 and AT video modes, disabling the built-in VGA, links 901 and 902, and the video DIP switches.
  12. ↑ John Elliott, "PC3086 DIP switches", seasip.info, 1 November 2003. Retrieved 2026-10-02.
  13. ↑ 14.0 14.1 John Elliott, "PC3086 option links", seasip.info, 23 January 2004. Retrieved 2026-10-02. Link functions from the user manual and the service manual schematic.
  14. ↑ 15.0 15.1 Amstrad plc, User Manual and MS-DOS Guide for the PC3086, PC3286 and PC3386SX, 2nd ed. (1990), pp. 9-1 to 9-3. Built-in IDE adaptors (XT type on the PC3086, AT type on the PC3286 and PC3386SX) and the hard disk type table.
  15. ↑ 16.0 16.1 16.2 John Elliott, "Using normal peripherals on Amstrad XTs", seasip.info. Retrieved 2026-10-02. Floppy cables and drives, hard drives and keyboards for the PC3086 and PC5086.
  16. ↑ John Elliott, "Amstrad XTs: Questions and Answers", seasip.info, 26 June 2019. Retrieved 2026-10-02. Setup utilities (DEVICE.COM on the PC2086 and PC3086, Ctrl-Alt-S on the PC5086) and Windows 3.0 on these machines.
  17. ↑ acpc.me (ACME) archive, Amstrad PC section, directory DOCUMENTS_TECHNIQUES/SERVICE_MANUALS. Retrieved 2026-10-02. The PC3086/PC3286/PC3386SX, PC4386SX and PC5086/PC5286 service manuals are listed with placeholder images only, marked missing.


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