Acorn Risc PC 700 Capacitor Guide

Acorn Risc PC 700 motherboard (board 1208,000). Like the 600, its surface-mount aluminium electrolytics leak with age and corrode the board.

This guide covers recapping the Acorn Risc PC 700 (board 1208,000). The 700 shares the Risc PC architecture and the same surface-mount-electrolyte failure mode as the Acorn Risc PC 600; the 1208,000 board is a revision of the 600's 0197,000 board that adds on-board 16-bit sound. The capacitor list below is the verified main-PCB list from the Acorn Risc PC Technical Reference Manual (which documents the 0197,000 board); it is the basis for the 700, but verify the sound-related positions against the actual 1208,000 board.

Safety

The Risc PC 700 has a fan-cooled mains switch-mode PSU. Disconnect the mains lead before opening the case. Board-level work is low voltage once the supply is disconnected, but the PSU module carries mains-side capacitors that hold charge.

Why the Risc PC must be recapped

The Risc PC main board uses surface-mount aluminium electrolytic capacitors that leak with age, corroding the pads and tracks — the same problem as the Acorn Archimedes A5000 and the Acorn A4 laptop. The Power On Self Test "RAM control line failure" code (00020000) is a classic result of leaked electrolyte on the RAM-control tracks (see Acorn Risc PC 700 Troubleshooting Guide). Recapping and cleaning the board is the key long-term task.

Capacitor list (recap targets)

The recap targets are the aluminium electrolytics and tantalums below; the ceramic decouplers are stable and are left in place.

Risc PC main PCB — surface-mount aluminium electrolytics

Value	Voltage	Designators	Qty
10 µF	16 V	C29, C53, C59, C60, C86, C90, C91, C133, C145, C164, C176	11
47 µF	16 V	C61, C74, C79, C87, C93, C116, C123, C136, C139, C172	10
4.7 µF	25 V	C70, C122	2
1 µF	50 V	C134	1

Risc PC main PCB — surface-mount tantalums and radial electrolytics

Value	Voltage	Type	Designators
10 µF	16 V	Tantalum (SMD)	C12, C64
47 µF	10 V	Tantalum (SMD)	C88
220 µF	16 V	Aluminium electrolytic (radial)	C2, C65, C73, C152, C161, C162
100 µF	25 V	Aluminium electrolytic (radial)	C168, C175

The surface-mount aluminium electrolytics are the leakage-prone parts and the priority for replacement. Because the 700's 1208,000 board carries the 16-bit sound circuitry on-board, treat the audio-section positions as the most likely to differ from this (0197,000) list and confirm them against the board.

Recap procedure

1. Disconnect the mains lead; remove the CPU card(s) and the drive slice, and lift out the main PCB.
2. Record every electrolytic (designator, value, voltage, polarity) before removing it.
3. Remove each surface-mount electrolytic with hot air, or by adding fresh solder to both terminals and rocking it off molten — do not lever a cold leaking part.
4. Clean the corrosive residue (isopropyl alcohol; mild alkaline clean then IPA for heavy electrolyte), inspect and repair corroded tracks (especially RAM-control lines).
5. Fit new 105 °C parts of equal value and equal-or-higher voltage, observing polarity. A reversed electrolytic fails short — double-check every one.
6. Check the on-board fuses FS1 (2 A) and FS2 (800 mA) for continuity while the board is out; replace the NiMH battery (BT1) if not already done.

Post-recap verification

1. Reassemble; reconnect the mains lead.
2. Power on and watch the POST run through purple/blue/purple to a normal RISC OS start (black screen with the memory-size message), with no red screen or floppy-LED fault code.
3. Confirm 16-bit sound and run a memory check.

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

Related pages

• Acorn Risc PC 700
• Acorn Risc PC 700 Maintenance Guide
• Acorn Risc PC 700 Troubleshooting Guide
• Acorn Risc PC 600 Capacitor Guide — the same list, from the 0197,000 board
• Capacitor Failure Symptoms