Acorn Archimedes A3010 Capacitor Guide

A3010 main PCB (0195,200 Issue 1). The main-board electrolytics are through-hole parts; the surface-mount electrolytics that owners recap are on the small audio hybrid card, not the main board. The on-board PSU is at the left edge.

This guide covers the capacitors on the Acorn Archimedes A3010 (ARM250 board, part 0195,200; early "Adelaide" board 0194,000), which carries its mains power supply on the main PCB. The A3010 is not a routine recap machine: its main-board electrolytics are through-hole parts, and the usual source of corrosion is the backup battery. The two capacitor-related jobs worth doing are the on-board PSU and the audio hybrid card.

⚠️ Safety

The A3010's PSU is built onto the main board, so the board carries mains voltages. Disconnect the mains lead before opening the case and discharge the PSU primary bulk capacitor before working near the power (left-hand) end of the board. Re-apply the earth-continuity and DC-insulation (class 1) safety tests after any internal work.

Is the A3010 a recap candidate?

The A3010 main board uses through-hole (leaded) aluminium electrolytics with surface-mount ceramic decouplers. It has no surface-mount electrolytic capacitors on the main board, so it is not affected by the surface-mount electrolyte leakage of the later Acorn machines (the A5000, the A4 laptop and the Risc PC). The main corrosion problem is instead the NiCd backup battery (see the Acorn Archimedes A3010 Maintenance Guide).

Surface-mount electrolytics do appear in one place: the audio hybrid card beside the mini-podule slot, which is the usual cause of sound crackle.

Board capacitors

Acorn documented the A3010 at module level, so there is no per-designator parts list in the Service Manual, and no published bill of materials for the A3010 main board. The exact values are legible on the Acorn A3010, A3020 and A4000 Technical Reference Manual circuit-diagram sheets (on the wiki) and can be read off each fitted part.

The main-board electrolytics are small-value aluminium types on the supply-filtering, floppy-power and analogue sections — the circuit-diagram sheet 1 shows examples such as 47 µF and 10 µF parts around the filtered +5 V supply and floppy-power area — with surface-mount ceramic decouplers (33 nF and smaller) across the IC supply pins. Because there is no official tabular list, this guide does not reproduce a per-designator table rather than risk publishing unverified values: record the value, voltage and polarity of each electrolytic before removing it and replace like-for-like with a 105 °C low-ESR part. Do not copy the Risc PC capacitor list onto the A3010 — they are different boards.

On-board PSU

The PSU section is part of the main PCB and includes the mains transformer, the primary bulk electrolytic, the low-voltage smoothing electrolytics for the +5 V and +12 V rails, and mains RFI-suppression capacitors on the input. Ageing PSU electrolytics are the documented cause of the A3010's slow or unreliable power-on and out-of-spec 5 V symptoms, and the fault gets worse under added load such as a memory upgrade.

Working on the PSU section:

• Unplug the mains lead and discharge the primary bulk capacitor before touching the primary side.
• Replace any smoothing electrolytic that is bulged, leaking or out of tolerance, reading the value, voltage and polarity off the fitted part.
• Replace any cracked mains-suppression capacitor with a correctly-rated safety (X/Y-class) part. Acorn does not name the fitted brand, so inspect and replace on condition.
• Re-apply the earth-continuity and insulation safety tests afterwards.

Audio hybrid card

The sound output stage is on a small hybrid daughter-card next to the mini-podule slot. Its surface-mount electrolytic capacitors degrade with age and, together with fractured card pins, cause crackle, pops or intermittent sound. If reseating or resoldering the card's connector does not cure the crackle, recap the hybrid's SMD electrolytics, reading each value off the fitted part and replacing with correctly-oriented low-ESR parts. The small ceramic and metallised-polyester filter capacitors on the card (values such as 22 nF and 100 nF) are not the usual fault.

Replacement procedure (board electrolytics)

1. Disconnect the mains lead; discharge the PSU primary capacitor; lift out the board.
2. Record each electrolytic's value, voltage and polarity (the silkscreen marks the positive pad).
3. Wet both leads with fresh flux and solder, lift each end in turn, and clear the holes with solder wick.
4. Fit the new part with correct polarity — a 105 °C low-ESR aluminium electrolytic of equal capacitance and equal-or-higher voltage.
5. Use a temperature-controlled iron and short dwell times to avoid lifting pads.
6. Inspect for clean joints and no bridges.

Post-recap verification

1. Reassemble and reconnect the mains lead.
2. Power on and confirm RISC OS reaches the desktop, first time and from cold.
3. Check the +5 V and +12 V rails are in tolerance and free of excessive ripple.
4. Run the audio, video and floppy functional tests.
5. Re-apply the earth-continuity and DC-insulation safety tests before returning the machine to service.

If a previously-working function fails after the recap, re-check the polarity of every replaced electrolytic first.

Related pages

• Acorn Archimedes A3010
• Acorn Archimedes A3010 Maintenance Guide
• Acorn Archimedes A3010 Troubleshooting Guide
• Acorn Archimedes A4000 Capacitor Guide — three-box sibling
• Acorn Archimedes A3000 Capacitor Guide — discrete-chip predecessor (full parts list)
• Capacitor Failure Symptoms