Amstrad PC4386SX Maintenance Guide
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Maintenance notes for the Amstrad PC4386SX. Amstrad's user manual and service manual for this model are not available online, so the notes below rest on Amstrad's brochure, Cliff Lawson's link tables from his time at Amstrad, and owners' repair reports.[1][2][3] Faults are in the Amstrad PC4386SX Troubleshooting Guide.
Safety
[edit | edit source]Warning: the power supply inside the system unit runs from the mains, and the monitor takes its mains supply through the system unit. Unplug the system unit before removing the cover.[2]
Amstrad's brochure describes a steel case with easy access to the memory, the expansion slots and the co-processor socket, but no published source describes how the cover is fixed.[2] Keep one hand on the metal case while working on the board.
Clock module
[edit | edit source]The clock and setup memory are in a Dallas DS1287 module, visible in Amstrad's photograph of the motherboard. Its built-in battery is quoted at a 10-year life, and when it is exhausted the BIOS reports "WARNING: CMOS battery failed".[2][4] Owners describe the module as socketed; one replaced it with a DS12887, which was still keeping time years later, and another repaired the original.[5][6] The same module is used in the Amstrad PC3086, and John Elliott's replacement procedure is in the PC3086 guide.[7] After fitting a new module, run SETUP with Ctrl-Alt-S.[3]
Memory
[edit | edit source]The PC4386SX takes four identical 30-pin parity SIMMs (three-chip or nine-chip types) rated between 80 and 150 ns. Four MB is standard and 16 MB the maximum.[3][2]
| Total | SIMMs | LK27 | LK28 | LK29 | LK30 |
|---|---|---|---|---|---|
| 1 MB | 4 × 256 KB | In | In | Out | Out |
| 4 MB | 4 × 1 MB | Out | In | In | Out |
| 16 MB | 4 × 4 MB | Out | Out | Out | Out |
| DRAM speed | LK25 | LK26 |
|---|---|---|
| 80 ns | Out | Out |
| 100 ns | Out | In |
| 120 ns | In | Out |
| 150 ns | In | In |
Source: Lawson's summary of the PC4386SX manual.[3]
Option links
[edit | edit source]| Link | Function |
|---|---|
| 10, 11, 12, 13 | Mouse interrupt: IRQ 5, 4, 9 or 3 |
| 14 | Speaker volume: pins 1 and 2 loud, pins 2 and 3 quiet |
| 16 | Power-on self test enable |
| 17 | On-board serial port (COM1) enable |
| 18 | On-board floppy controller enable |
| 19 | On-board parallel port (LPT1) enable |
| 20 | On-board mouse interface enable |
| 23 | On-board VGA enable |
| 24 | On-board hard disk controller enable |
| 25, 26 | DRAM speed |
| 27 to 30 | Memory size |
| 33 | Expansion bus cache enable |
To use a serial mouse, remove the mouse interface link (LK20); Lawson notes that the /C switch of MOUSE.COM does not disable the built-in interface by itself.[3][8]
Co-processor
[edit | edit source]The board has a socket for an 80387SX-20, which Amstrad lists as a user upgrade. In Amstrad's photograph it is the empty square socket near the processor.[2]
Power supply
[edit | edit source]
No circuit or rating for the supply has been published. Two owners on Vogons worked out its connectors in 2021 while one of them replaced a burned-out supply:[6]
| Connector | Wire or pin | Voltage |
|---|---|---|
| Main connector to the motherboard | Yellow | +12 V |
| Black | Ground | |
| Pink | +5 V | |
| Small four-way connector (SK106 on the board) | Pin 1, red | −5 V |
| Pin 2 | −12 V | |
| Pin 3 | Ground | |
| Pin 4 | +5 V, switched (see below) | |
| Three-way lead | Black, brown, red | Ground, +12 V, +5 V |
The owner rebuilding the supply traced SK106 pins 1 to 3 to the −5 V, −12 V and ground pins of the ISA slots, and found that the board showed a picture only when pin 4 was connected to +5 V (or 3.3 V) one or two seconds after power-on. He concluded that the original supply switches this line, possibly through a transistor, and fitted a second switch while testing. His replacement was based on a picoPSU, with an LM2662 converter planned for the negative rails.[6] Similar colours are reported for the PC5286's supply (see the PC5286 guide).
Drives
[edit | edit source]- The floppy drive is the same proprietary 26-way type as in the PC5086 and PC5286, and new belts have not revived failed drives. A Gotek running FlashFloppy worked with the 26-way to 34-way adapter wiring given in the PC5086 guide.[6]
- One owner describes the hard disk's power connector as non-standard. The supply's three-way lead (ground, +12 V, +5 V) is shown above; the owner who photographed it did not say which drive it feeds.[9][6]
- The 80 MB drive was fitted as standard; an owner who restored a machine set it up again in SETUP after repairing the clock.[2][6]
See Floppy Drive Repair and Hard Drive Maintenance and Repair.
Capacitors
[edit | edit source]No capacitor values have been published for the PC4386SX's motherboard or power supply; the service manual is listed as missing from the acpc.me archive and no scan is known.[1] See Capacitor Failure Symptoms and the Amstrad PC4386SX Capacitor Replacement Guide.
Related pages
[edit | edit source]- Amstrad PC4386SX · Amstrad PC4386SX Troubleshooting Guide
- Amstrad PC5086 Maintenance Guide · Amstrad PC5286 Maintenance Guide · Amstrad PC3086 Maintenance Guide
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 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.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Amstrad plc, PC4386SX brochure, © March 1991, pp. 4–5 (feature highlights, motherboard photograph, specification table). Hosted as File:Amstrad PC4386SX brochure (1991).pdf.
- ↑ 3.0 3.1 3.2 3.3 3.4 Cliff Lawson (Amstrad plc), "Older AT PCs" (atpcs.htm), from his Amstrad support pages at web.ukonline.co.uk/cliff.lawson, as preserved at freetimeweb.nl. Retrieved 2026-10-02. SETUP on the 3xxx and 4xxx series, the BIOS 2.xx of the 3xxx series, memory links for the 3286, 3386SX and 4386SX, video DIP switches and option links.
- ↑ Centre for Computing History, "Amstrad PC4386SX Computer" (CH63138), 1991. Retrieved 2026-10-02. Photographs of a complete system showing "WARNING: CMOS battery failed".
- ↑ Vogons forum, JidaiGeki's replies in "Amstrad 5086 - worth a go?" (March 2016) and "Amstrad 3286" (September 2024). Retrieved 2026-10-02. The PC4386SX's socketed Dallas clock module, replaced with a DS12887.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Vogons forum, "AMSTRAD PC 5086 - Floppy Drive Problems", Perro, tecnico, Jason_rg, flufetor, aotta69 and gca, May 2020 to August 2021. Retrieved 2026-10-02. Belt replacement on the original drives, a 26-pin to 34-pin adapter, capacitor failures in PC5286 power supplies and boards, and the PC4386SX power connector pinout.
- ↑ 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.
- ↑ Cliff Lawson (Amstrad plc), "General notes on Amstrad PCs" (general.htm), as preserved at freetimeweb.nl. Retrieved 2026-10-02. Amstrad's proprietary keyboard and mouse interfaces up to the 4386, PS/2-compatible ones from the 5xxx series, and a summary specification of each PC.
- ↑ Vogons forum, "Amstrad Adlib Clone: Restoration and Testing", brassicGamer and others, April 2016 to May 2017. Retrieved 2026-10-02. The Amstrad OPL2 sound card 3100-015P-4 bundled with the PC5286; gca reports the same card in his PC4386SX.