Editing Acorn Risc PC 700 Capacitor Guide

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[[File:Acorn Risc PC 700 motherboard.jpg|thumb|360x360px|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.<ref name="trm">[[Acorn Risc PC Technical Reference Manual]] (Issue 1, September 1994; part 0497,057), Acorn Computers &mdash; 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.

== 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 &mdash; 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.

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Risc PC main PCB &mdash; 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
|}

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Risc PC main PCB &mdash; 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.<ref name="trm" />

== Recap procedure ==

# 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 &mdash; 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 &mdash; 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 ==

# 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 ==

* [[Acorn Risc PC 700]]
* [[Acorn Risc PC 700 Maintenance Guide]]
* [[Acorn Risc PC 700 Troubleshooting Guide]]
* [[Acorn Risc PC 600 Capacitor Guide]] &mdash; the same list, from the 0197,000 board
* [[Capacitor Failure Symptoms]]

== References ==

<references />

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[[Category:Acorn Computers]]
[[Category:Capacitor Replacement Guides]]