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Amstrad PC7386SX Maintenance Guide

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Amstrad PC7386SX main PCB layout
PC7386SX main board VSC386SXD V.2.01 (service manual top view). The backup battery is drawn at upper right beside the power header CON1.

Amstrad's service manual for the Amstrad PC7386SX gives the case layout, the backup battery circuit, the memory and video RAM positions, the drive part numbers and the safety tests to make after a repair.[1] The Amstrad Mega PC Maintenance Guide covers the same main board in the Mega PC, plus its games card and monitor. Faults are in the Amstrad PC7386SX Troubleshooting Guide and capacitor values in the Amstrad PC7386SX Capacitor Replacement Guide.

Safety

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Warning: the power supply module (DE-3) at the rear of the case carries mains voltage. Unplug the mains lead before removing any screws.

Amstrad's safety tests after any work on the unit are:[1]

  1. Flash test at 1.5 kV RMS for 3 s between the joined live and neutral of the mains lead and all accessible metal on the outside of the set.
  2. Insulation test at 1.5 kV RMS for 3 s, showing a resistance greater than 4 MΩ.
  3. Earth continuity: the resistance of the mains lead must not exceed 0.5 Ω.

Parts marked with a warning triangle in the parts list, such as the power supply module and the fuse resistor F1, are safety items and must be replaced with parts of identical specification.[1]

Opening the case

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The cabinet exploded view shows the top cabinet (A-18) held by screws (L-12) along its top rear edge and sides. Under it are the drive bracket (B-1) at the front left with the floppy drive (DE-2) above the hard disc (DE-1), the expansion riser (DE-17) carrying the two ISA slots, the main board (DE-6) on the bottom chassis (A-17), the speaker (DE-10) and the power supply module (DE-3) at the rear right. The volume control (DE-9) and its knob (A-4) are on the rear chassis assembly (A-19).[1]

  1. Switch off, then disconnect the mains lead, the monitor's power lead, the keyboard, the mouse and any other cables.
  2. Remove the cover screws and slide the top cabinet off.
  3. Note the routing of the floppy and hard disc cables (Amstrad parts 273925 and 273926) and the front panel cable before unplugging anything.
  4. Wear an earthed wrist strap when handling the main board, SIMMs and cards.

Backup battery

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Schematic 6/13 shows a 3.6 V battery (BATT) feeding the WD76C20's battery input (VBATT) through a 1N4148 diode and a 1 kΩ resistor (D8, R26). A four-pin header, J9, marked "EXT. BATT" on the board, takes an external battery through D7 and R27.[1] On a Mega PC board of the same revision, photographed for Wikimedia Commons, the battery is a blue cylindrical cell soldered next to the power header.[2]

  1. Before touching the battery, enter the setup program and write down the hard disc's cylinders, heads and sectors. The BIOS has no automatic drive detection, so these must be typed in again.[3]
  2. Inspect the cell and the board around it for electrolyte, green or white deposits and lifted solder mask. Clean any damage as described in Battery Explosion, Capacitor or Corrosion Damage.
  3. Remove a leaking cell even if the machine still keeps time. Either fit a replacement of the same voltage in the same position or connect an external battery to J9.
  4. Check C60 (1 µF 16 V) on the battery line at the same time; it sits in the area most exposed to leakage.[1]

Memory

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Amstrad's specification says memory is expanded "via 4 SIMM sockets (up to 16Mb)", with 1 MB fitted in the 40 MB model and 2 MB in the 80 MB model. The top view and schematic 2/13 both show eight 30-pin SIMM positions (U2–U9), arranged as banks 0 to 3 with an H and an L position in each.[1] On a Mega PC board of the same revision only banks 0 and 1 (U2–U5) have sockets fitted, so check how many sockets your board has before buying memory.[2] The H and L sockets carry the high and low bytes of the 386SX's 16-bit data bus, so a bank takes a matched pair of SIMMs. In 1993 a dealer sold 2 MB and 4 MB upgrade kits listed for both the PC7286 and the PC7386SX.[4]

  • Fill a bank with two SIMMs of the same size and speed, one in the H socket and one in the L socket.
  • Reseat and clean the SIMM contacts with isopropyl alcohol if the memory count is wrong at switch-on.

Video RAM

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Video memory is 256 KB as standard, expandable to 512 KB.[1] Schematic 12/13 draws two 44256 DRAMs (U51, U52) and two further positions, U53 and U54, inside a box marked "512K option". The parts list gives U51 and U52 as 44256-8 DIP parts, but the top view labels all four positions "4464-80". Check what is fitted on your board and match it when filling U53 and U54.[1]

Drives

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Drives in the parts list
Ref Drive Amstrad part no.
DE-2 Floppy drive, Sony MP-F17W-10 (3.5-inch, 1.44 MB) 272723
DE-1 Seagate ST351 (AX), 40 MB, UK formatted / unformatted 273908 / 275001
DE-1 Sony 80 MB, UK formatted / unformatted 373909 / 41182

Source: electrical parts list, p. 19.[1] See Floppy Drive Repair and Hard Drive Maintenance and Repair.

Owners replacing the original hard disc with a larger drive or a CompactFlash adapter report that the on-board IDE interface accepts few modern drives. Two fixes reported on Vogons are an ISA IDE controller in the spare slot, or OnTrack Disk Manager installed on the card to replace the BIOS disc routines.[3][5] The Amstrad PC7386SX Troubleshooting Guide gives the details.

Keyboard, mouse and ports

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The keyboard and mouse sockets (CON3, CON4) take +5 V through a 2 A fuse resistor, F1 (BEL 2A MQ, part 273945), and the inductor L2.[1] Both sockets share F1, so a short in either lead leaves the keyboard and the mouse without power. Plug and unplug them with the machine switched off.

Tools

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  • Cross-head screwdrivers and an earthed wrist strap
  • Digital multimeter for the rails at CON1 and for F1
  • Isopropyl alcohol and lint-free swabs
  • Desoldering tool for the battery and capacitors
  • See Recommended Tools.
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Amstrad plc, PC7386SX Personal Colour Computer Service Manual, first published October 1992. Hosted as File:Amstrad PC7386SX Service Manual.pdf, described at Amstrad PC7386SX Service Manual. Technical specification and safety tests p. 2; main PCB top view p. 3; schematic diagrams 1/13 (p. 5), 2/13 (p. 6), 6/13 (p. 10), 12/13 (p. 16); cabinet exploded view p. 18; parts lists p. 19.
  2. ↑ 2.0 2.1 Mister rf, "Amstrad VSC386SXD V2.01.jpg", Wikimedia Commons, 2022 (CC BY-SA 4.0). Retrieved 2026-10-02. Main board marked VSC386SXD V2.01 with the blue cylindrical battery beside the power header.
  3. ↑ 3.0 3.1 Vogons forum, "Amstrad PC7386SX Hard Drive issues". Retrieved 2026-10-02. Owners of a PC7386SX board and a Mega PC report that the BIOS has no auto-detect, that drives are entered as a user type, and that many modern drives give "Fixed Disk Controller Failure".
  4. ↑ Practical PC vol. 2 issue 6, June 1993, memory dealer advertisement: "PC7286, 7386 2MB £72 4MB £136". Scan at archive.org. Retrieved 2026-10-02.
  5. ↑ Vogons forum, "Amstrad 386 PC won't boot from compact flash but WILL install to it". Retrieved 2026-10-02. A Mega PC (PC7386SX board) that installed DOS 6.22 on a 512 MB CompactFlash card but would not boot from it; booting worked once OnTrack Disk Manager was used, and an XT-IDE BIOS on a network card is suggested as an alternative.


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