Acorn Risc PC 700 Capacitor Guide: Difference between revisions
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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.<ref name="trm">[[Acorn Risc PC Technical Reference Manual]] (Issue 1, September 1994; part 0497,057), Acorn Computers — hosted on this wiki. Main-PCB assembly parts list: capacitor designators, values, types and Acorn part numbers; also the on-board fuses and the NiMH battery. The parts list is for the original 0197,000 board; the 700's 1208,000 board is a revision with on-board 16-bit sound.</ref> | 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.<ref name="trm">[[Acorn Risc PC Technical Reference Manual]] (Issue 1, September 1994; part 0497,057), Acorn Computers — hosted on this wiki. Main-PCB assembly parts list: capacitor designators, values, types and Acorn part numbers; also the on-board fuses and the NiMH battery. The parts list is for the original 0197,000 board; the 700's 1208,000 board is a revision with on-board 16-bit sound.</ref> | ||
== | == 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. | 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. | ||
Latest revision as of 10:50, 27 September 2026
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.[1]
Safety
[edit | edit source]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
[edit | edit source]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)
[edit | edit source]The recap targets are the aluminium electrolytics and tantalums below; the ceramic decouplers are stable and are left in place.
| 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 |
| 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.[1]
Recap procedure
[edit | edit source]- Disconnect the mains lead; remove the CPU card(s) and the drive slice, and lift out the main PCB.
- Record every electrolytic (designator, value, voltage, polarity) before removing it.
- 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.
- Clean the corrosive residue (isopropyl alcohol; mild alkaline clean then IPA for heavy electrolyte), inspect and repair corroded tracks (especially RAM-control lines).
- Fit new 105 °C parts of equal value and equal-or-higher voltage, observing polarity. A reversed electrolytic fails short — double-check every one.
- 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
[edit | edit source]- Reassemble; reconnect the mains lead.
- 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.
- 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
[edit | edit source]- 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
References
[edit | edit source]- ↑ 1.0 1.1 Acorn Risc PC Technical Reference Manual (Issue 1, September 1994; part 0497,057), Acorn Computers — hosted on this wiki. Main-PCB assembly parts list: capacitor designators, values, types and Acorn part numbers; also the on-board fuses and the NiMH battery. The parts list is for the original 0197,000 board; the 700's 1208,000 board is a revision with on-board 16-bit sound.