Editing Acorn Risc PC 600 Capacitor Guide

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[[File:Acorn Risc PC 600 motherboard.jpg|thumb|360x360px|Acorn Risc PC 600 motherboard (0197,000). The surface-mount aluminium electrolytics scattered across the board leak with age and corrode the pads and tracks.]]

This guide lists the capacitors on the '''[[Acorn Risc PC 600]]''' main PCB (board 0197,000) and covers the recap. The values, designators and Acorn part numbers are taken directly from the [[Acorn Risc PC Technical Reference Manual]] main-PCB assembly parts list.<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 ("ALEC" aluminium electrolytic, "TANT" tantalum, "DCPLR"/"CML" ceramic) and Acorn part numbers; also the on-board fuses and the NiMH battery.</ref>

== ⚠️ Safety ==

The Risc PC has a fan-cooled mains switch-mode PSU. '''Disconnect the mains lead before opening the case.''' Board-level capacitor work is low voltage once the supply is disconnected, but the PSU module carries mains-side capacitors that hold charge &mdash; treat it as any mains switch-mode supply.

== Why the Risc PC must be recapped ==

The Risc PC main board uses surface-mount aluminium electrolytic capacitors. As on the [[Acorn Archimedes A5000]] and the Acorn A4 laptop, the electrolyte leaks with age and corrodes the pads and tracks, producing progressive and intermittent faults &mdash; the Power On Self Test "'''RAM control line failure'''" code (00020000) is a classic result of leaked electrolyte attacking the RAM-control tracks (see [[Acorn Risc PC 600 Troubleshooting Guide]]). Replacing the surface-mount electrolytics and cleaning the board is the key long-term maintenance task.

== Capacitor list (recap targets) ==

The recap targets are the aluminium electrolytics and tantalums below. The many ceramic decouplers (33 nF "DCPLR", and the 100 pF/1 nF/etc. "CML" parts) 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'''
! Value !! Voltage !! Designators !! Qty
|-
| 10 µF || 16 V || C12, C64 || 2
|-
| 47 µF || 10 V || C88 || 1
|}

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Risc PC main PCB &mdash; through-hole radial electrolytics'''
! Value !! Voltage !! Designators !! Qty
|-
| 220 µF || 16 V || C2, C65, C73, C152, C161, C162 || 6
|-
| 100 µF || 25 V || C168, C175 || 2
|}

The surface-mount aluminium electrolytics are the leakage-prone parts and the priority for replacement; the tantalums and the radial electrolytics are replaced on a full recap. (C68, C76, C89 and C137 are listed as "not fitted" in the parts list.)<ref name="trm" />

== Recap procedure ==

# Disconnect the mains lead; remove the CPU card(s) and the drive slice, and lift out the main PCB.
# Photograph the board and '''record every electrolytic''' (designator, value, voltage, polarity). The polarity band on a surface-mount electrolytic must agree with the marked pad.
# Remove each surface-mount electrolytic with '''hot air''', or by adding fresh solder to both terminals and rocking the part off with the joints molten. Do not lever a cold leaking part &mdash; it tears pads.
# '''Clean the corrosion''': neutralise and wash the residue (isopropyl alcohol; a mild alkaline clean then IPA for heavy electrolyte), inspect each pad and track, and repair corroded or open tracks (particularly the RAM-control lines) with fine wire before fitting new parts.
# Fit new '''105 °C''' parts of equal capacitance and equal-or-higher voltage, observing polarity. A reversed electrolytic fails short &mdash; double-check every one.
# Re-inspect under magnification for bridges and lifted pads.

== On-board fuses and PSU ==

While the board is out, check the on-board surface-mount fuses '''FS1 (2 A)''' and '''FS2 (800 mA)''' for continuity.<ref name="trm" /> The mains PSU is a separate module; if it is unstable, service it only if competent with mains switch-mode supplies (discharge the primary bulk capacitor first), or exchange it. Replace the NiMH backup battery (BT1) at the same time if it has not been done (see [[Acorn Risc PC 600 Maintenance Guide]]).

== Post-recap verification ==

# Reassemble; reconnect the mains lead.
# Power on and watch the POST: the screen should pass through purple/blue/purple and start RISC OS (black screen with the memory-size message), with no red screen or floppy-LED fault code.
# Confirm sound is restored and run a memory check.

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

== Note for the Risc PC 700 ==

The Risc PC 700 uses the revised 1208,000 board (with on-board 16-bit sound). It shares the same surface-mount-electrolytic recap profile; the list above (from the original 0197,000 board) is the basis, but verify the sound-related positions against the actual 700 board. See [[Acorn Risc PC 700 Capacitor Guide]].

== Related pages ==

* [[Acorn Risc PC 600]]
* [[Acorn Risc PC 600 Maintenance Guide]]
* [[Acorn Risc PC 600 Troubleshooting Guide]]
* [[Acorn Risc PC 700 Capacitor Guide]] · [[Capacitor Failure Symptoms]]

== References ==

<references />

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