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Amstrad PC4386SX Capacitor Replacement Guide

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Amstrad PC4386SX main board (1991 brochure)
PC4386SX motherboard in Amstrad's 1991 brochure. The riser card along the top carries four small radial electrolytics.

The Amstrad PC4386SX keeps its electrolytic capacitors in the power supply, on the motherboard and on the riser card that carries the two expansion slots. Amstrad's service manual for the PC4386SX, which also covered its PC-10HRCDR and PC-10MDR monitors, is listed as missing in the acpc.me archive, and no scan of it is known; no capacitor values have been published for any part of the machine.[1]

Safety

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Warning: the supply inside the system unit runs from the mains, and the monitor's mains supply is switched through the system unit.[2]

  • Unplug the system unit and the monitor before opening the case.
  • Measure across the supply's large primary capacitor before touching its board.
  • An owner who built a replacement supply found that the board needs one +5 V line to come up after the others; the connector details are in the PC4386SX Maintenance Guide.[3]

What is known

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PC4386SX electrolytics
Assembly What is known Source
Riser card MS0213A Four small radial electrolytics, two at each end of the card beside the slot connectors. Values not legible Amstrad's brochure photograph[2]
Motherboard The brochure photograph shows the processor, the Dallas DS1287 clock module at the left and the ROMs; no electrolytic can be identified on the part of the board in view Amstrad's brochure photograph[2]
Power supply No rating, circuit or parts list published. One owner replaced a burned-out supply and worked out its connectors; he did not say which part failed Owner's report[3]
Monitor (PC-10HRCDR or PC-10MDR) A separate unit with its own boards; the same missing service manual covered it acpc.me listing[1]

The DS1287 module holds its own lithium cell, so there is no separate backup battery on the motherboard. A failed module gives "WARNING: CMOS battery failed" and is a module replacement, not a capacitor fault.[4][2]

Recording your own boards

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  1. Photograph the motherboard, the riser card and the supply board from above. Include the board numbers; MS0213A is printed on the riser.[2]
  2. Record each electrolytic's designator, capacitance, voltage, temperature rating, size and polarity, read from the part itself.
  3. Read values from your own boards, not from another Amstrad model's list.

Procedure

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  1. Unplug the system unit and the monitor.
  2. Open the case. Amstrad's brochure promises easy access to the memory, slots and co-processor socket but does not say how the cover is fixed, so find every screw before prying at a panel.[2]
  3. Label the supply's leads, including the small four-way lead to SK106, before unplugging them.[3]
  4. Lift out the riser card to reach its four electrolytics, and replace them one at a time with parts of the same capacitance, the same or a higher voltage rating and the same polarity.
  5. Work through the supply and motherboard the same way, then refit the riser and leads.

After the recap

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Switch on with the monitor connected. If the board shows no picture, check first that every lead is back on its connector; an owner who wired a substitute supply found that the board started only when the +5 V line on SK106 pin 4 came up a second or two after the other rails.[3] Faults are covered in the Amstrad PC4386SX Troubleshooting Guide.

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References

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  1. ↑ 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. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Amstrad plc, PC4386SX brochure, © March 1991, pp. 4–5 (feature highlights, motherboard photograph and specification table: 20 MHz 80386SX, 4 MB standard, two half-length 16-bit ISA slots, easy access to RAM, slots and the 80387SX socket, steel system case, mains power for the monitor switched through the system unit). Hosted as File:Amstrad PC4386SX brochure (1991).pdf.
  3. ↑ 3.0 3.1 3.2 3.3 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. The PC4386SX power connector pinout, an owner's rebuild of a burned-out supply, and the switched +5 V line on the motherboard's four-way connector SK106.
  4. ↑ Centre for Computing History, "Amstrad PC4386SX Computer" (CH63138), 1991. Retrieved 2026-10-21. Photographs of a complete system showing "WARNING: CMOS battery failed".


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