Acorn Archimedes A3000 Capacitor Guide - Revision history

Josh: Rebuild capacitor list from Service Manual pp. 52-54: add missing C93-C112 (four electrolytics, two axials, four tantalums), upgrade boards, part numbers; correct C74; add Acorn's fault-procedure capacitors; drop uncited PSU recap and RIFA advice

2026-10-01T06:42:52Z

Rebuild capacitor list from Service Manual pp. 52-54: add missing C93-C112 (four electrolytics, two axials, four tantalums), upgrade boards, part numbers; correct C74; add Acorn's fault-procedure capacitors; drop uncited PSU recap and RIFA advice

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Josh: Remove emoji from section headings; de-duplicate ref definitions that produced visible cite errors; merge the duplicated References section; targeted corrections noted in the drive report

2026-09-27T09:50:19Z

Remove emoji from section headings; de-duplicate ref definitions that produced visible cite errors; merge the duplicated References section; targeted corrections noted in the drive report

← Older revision		Revision as of 10:50, 27 September 2026
Line 4:		Line 4:
	This guide lists the capacitors on the '''[[Acorn Archimedes A3000]]''' main PCB and covers the recap. The values, designators and Acorn part numbers come directly from the [[Acorn A3000 Service Manual]] PCB assembly parts list.<ref name="sm">[[Acorn A3000 Service Manual]], Acorn Computers — hosted on this wiki. PCB assembly parts list: capacitor designators C1–C91, values, types ("ALEC" aluminium electrolytic, "TANT" tantalum, "DCPLR" SMD ceramic decoupler, "CPLT" plate ceramic) and Acorn part numbers; also the PSU output spec and mains-hazard warning.</ref>		This guide lists the capacitors on the '''[[Acorn Archimedes A3000]]''' main PCB and covers the recap. The values, designators and Acorn part numbers come directly from the [[Acorn A3000 Service Manual]] PCB assembly parts list.<ref name="sm">[[Acorn A3000 Service Manual]], Acorn Computers — hosted on this wiki. PCB assembly parts list: capacitor designators C1–C91, values, types ("ALEC" aluminium electrolytic, "TANT" tantalum, "DCPLR" SMD ceramic decoupler, "CPLT" plate ceramic) and Acorn part numbers; also the PSU output spec and mains-hazard warning.</ref>

	== ⚠️ Safety ==		== Safety ==

	The A3000 contains a mains-powered 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 itself carries mains-side capacitors that can hold charge — treat the PSU module with the same caution as any mains switch-mode supply (see the PSU section below).		The A3000 contains a mains-powered 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 itself carries mains-side capacitors that can hold charge — treat the PSU module with the same caution as any mains switch-mode supply (see the PSU section below).

Josh: PSU: permit safe servicing/recap of the mains PSU for restoration; strengthen lethal-shock warnings and discharge procedure (replaces exchange-only/do-not-open wording)

2026-07-19T08:56:20Z

PSU: permit safe servicing/recap of the mains PSU for restoration; strengthen lethal-shock warnings and discharge procedure (replaces exchange-only/do-not-open wording)

← Older revision		Revision as of 09:56, 19 July 2026
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	== PSU module ==		== PSU module ==

	The A3000's switch-mode PSU is a separate cased module~~. It contains~~ mains-side suppression capacitors and bulk smoothing electrolytics~~. The Service Manual treats the PSU as a non-serviceable assembly~~ (output 5 V at up to 4.4 A, 22 W; ripple should be within 50 mV pk-pk).<ref name="sm" /> ~~If the +5 V~~ shows ripple or the machine ~~resets randomly, either replace~~ the PSU ~~module or,~~ if you are competent with mains switch-mode supplies, ~~recap it:~~ discharge the primary ~~bulk capacitor first~~, then replace the electrolytics and any cracked mains-suppression (RIFA-style) capacitor with ~~correctly~~-rated ~~parts~~. Read each value off the fitted part.		The A3000's switch-mode PSU is a separate cased module containing mains-side suppression capacitors and bulk smoothing electrolytics (output 5 V at up to 4.4 A, 22 W; ripple should be within 50 mV pk-pk).<ref name="sm" /> Acorn's service manual treated it as an exchange unit, but replacement modules are long gone, so a supply that shows ripple or causes random resets is '''recapped'''.

			'''Danger:''' the primary side and the reservoir and mains-suppression capacitors can hold a '''lethal charge after the machine is unplugged''' — a shock from them can be fatal. Only work on the PSU if you are competent with mains switch-mode supplies. Unplug the mains lead, '''discharge the reservoir capacitor through a bleeder resistor and confirm 0 V with a meter''' before touching the primary side, then replace the electrolytics and any cracked mains-suppression (RIFA-style) capacitor — the suppression parts must be replaced with safety-rated X/Y-class capacitors, never ordinary ones. Read each value off the fitted part, and re-apply the earth-continuity and insulation safety tests afterward.

	== Post-recap verification ==		== Post-recap verification ==

Josh: Create: full capacitor list + recap (from A3000 Service Manual parts list)

2026-06-17T20:07:09Z

Create: full capacitor list + recap (from A3000 Service Manual parts list)

New page

<templatestyles src="Template:StyledTable/styles.css" />
[[File:Acorn Archimedes A3000 motherboard.jpg|thumb|360x360px|Acorn A3000 main PCB. The board electrolytics are leaded radial/axial cans; the small surface-mount parts are ceramic decouplers, not electrolytics.]]

This guide lists the capacitors on the '''[[Acorn Archimedes A3000]]''' main PCB and covers the recap. The values, designators and Acorn part numbers come directly from the [[Acorn A3000 Service Manual]] PCB assembly parts list.<ref name="sm">[[Acorn A3000 Service Manual]], Acorn Computers — hosted on this wiki. PCB assembly parts list: capacitor designators C1–C91, values, types ("ALEC" aluminium electrolytic, "TANT" tantalum, "DCPLR" SMD ceramic decoupler, "CPLT" plate ceramic) and Acorn part numbers; also the PSU output spec and mains-hazard warning.</ref>

== ⚠️ Safety ==

The A3000 contains a mains-powered 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 itself carries mains-side capacitors that can hold charge — treat the PSU module with the same caution as any mains switch-mode supply (see the PSU section below).

== Is the A3000 a recap candidate? ==

The A3000 board uses '''leaded aluminium electrolytics and tantalums''', not the leaking surface-mount electrolytics of the later [[Acorn Archimedes A5000]], A4 laptop and Risc PC. The board therefore ages gently; the urgent items on an A3000 are the '''CMOS backup battery''' (which leaks and corrodes the bottom-left corner — see [[Acorn Archimedes A3000 Maintenance Guide]]) and the '''PSU module'''. A board recap is still reasonable on a 35-year-old machine that is already open, or to chase ripple-related instability.

== Visual inspection ==

Check each electrolytic for a bulged or vented top, leaked electrolyte, a cracked sleeve, or a tired joint. The radial electrolytics cluster around the supply and audio sections; the two axial parts (C39, C83) are 47 µF/10 V.

== Acorn A3000 capacitor list (electrolytic and tantalum) ==

These are the recap targets — the ceramic decouplers (33 nF/100 nF SMD) and plate ceramics are stable and are left in place.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''A3000 main PCB — aluminium electrolytic capacitors'''
! Designator !! Value !! Voltage !! Mounting
|-
| C6, C7, C8, C9, C10 || 10 µF || 16 V || Radial
|-
| C19 || 10 µF || 16 V || Radial
|-
| C67 || 4.7 µF || 16 V || Radial
|-
| C15, C60, C63 || 47 µF || 16 V || Radial
|-
| C39, C83 || 47 µF || 10 V || Axial
|-
| C65, C70 || 100 µF || 25 V || Radial
|-
| C12, C14, C61, C66, C69 || 220 µF || 16 V || Radial
|}

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''A3000 main PCB — tantalum capacitors'''
! Designator !! Value !! Voltage
|-
| C4, C13, C22, C34, C55, C57, C78, C89 || 10 µF || 10 V
|}

The remaining board capacitors are ceramic and not normally replaced: 33 nF and 100 nF surface-mount decouplers (the "DCPLR 1210" parts, e.g. C1, C5, C11, C17, C18, C20, C21, C35–C37, C40–C54, C56, C58, C59, C64, C71–C74, C76, C84, C87) and plate ceramics (33 pF C2, 12 pF C16, 100 pF C23/C32/C33, 1 nF C79/C85, 2.2 nF C24–C31/C75/C81/C82/C86/C90/C91), plus a few 47 nF ceramics (C3, C62, C68, C74) and 100 nF/22 nF polyester (C80/C88, C77).<ref name="sm" />

== Replacement summary ==

Use 105 °C low-ESR aluminium electrolytics of equal capacitance and equal-or-higher voltage; tantalums may be replaced with tantalum or a good electrolytic of equal value.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Board recap shopping list'''
! Value !! Voltage !! Type !! Qty
|-
| 4.7 µF || 16 V || Electrolytic (radial) || 1
|-
| 10 µF || 16 V || Electrolytic (radial) || 6
|-
| 10 µF || 10 V || Tantalum || 8
|-
| 47 µF || 16 V || Electrolytic (radial) || 3
|-
| 47 µF || 10 V || Electrolytic (axial) || 2
|-
| 100 µF || 25 V || Electrolytic (radial) || 2
|-
| 220 µF || 16 V || Electrolytic (radial) || 5
|}

== Replacement procedure ==

# Disconnect the mains lead; open the case and remove the main PCB.
# Mark the polarity of each electrolytic/tantalum before removal (the silkscreen marks the positive pad).
# Wet both leads with fresh solder/flux, lift each end in turn, and clear the holes with solder wick.
# Fit the new part with correct polarity, solder and trim. Reverse-fitted tantalums fail short, so double-check C4/C13/C22/C34/C55/C57/C78/C89.
# Inspect for clean joints and no bridges before reassembly.

== PSU module ==

The A3000's switch-mode PSU is a separate cased module. It contains mains-side suppression capacitors and bulk smoothing electrolytics. The Service Manual treats the PSU as a non-serviceable assembly (output 5 V at up to 4.4 A, 22 W; ripple should be within 50 mV pk-pk).<ref name="sm" /> If the +5 V shows ripple or the machine resets randomly, either replace the PSU module or, if you are competent with mains switch-mode supplies, recap it: discharge the primary bulk capacitor first, then replace the electrolytics and any cracked mains-suppression (RIFA-style) capacitor with correctly-rated parts. Read each value off the fitted part.

== Post-recap verification ==

# Reassemble; reconnect the mains lead.
# Power on and confirm RISC OS reaches the desktop.
# Measure the +5 V rail (4.9–5.1 V) and check ripple is within 50 mV pk-pk.
# Confirm sound (the A3000 has stereo output) and a floppy access.

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

== Related pages ==

* [[Acorn Archimedes A3000]]
* [[Acorn Archimedes A3000 Maintenance Guide]]
* [[Acorn Archimedes A3000 Troubleshooting Guide]]
* [[Acorn Archimedes A4000 Capacitor Guide]]
* [[Capacitor Failure Symptoms]]

== References ==

<references />

{{Navbox-AcornComputers|state=collapsed}}

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