Editing Acorn Archimedes A3000 Capacitor Guide

<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 &mdash; hosted on this wiki. PCB assembly parts list: capacitor designators C1&ndash;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 &mdash; 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 &mdash; 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&nbsp;µF/10&nbsp;V.

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

These are the recap targets &mdash; the ceramic decouplers (33&nbsp;nF/100&nbsp;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 &mdash; aluminium electrolytic capacitors'''
! Designator !! Value !! Voltage !! Mounting
|-
| C6, C7, C8, C9, C10 || 10&nbsp;µF || 16&nbsp;V || Radial
|-
| C19 || 10&nbsp;µF || 16&nbsp;V || Radial
|-
| C67 || 4.7&nbsp;µF || 16&nbsp;V || Radial
|-
| C15, C60, C63 || 47&nbsp;µF || 16&nbsp;V || Radial
|-
| C39, C83 || 47&nbsp;µF || 10&nbsp;V || Axial
|-
| C65, C70 || 100&nbsp;µF || 25&nbsp;V || Radial
|-
| C12, C14, C61, C66, C69 || 220&nbsp;µF || 16&nbsp;V || Radial
|}

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

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

== Replacement summary ==

Use 105&nbsp;°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&nbsp;µF || 16&nbsp;V || Electrolytic (radial) || 1
|-
| 10&nbsp;µF || 16&nbsp;V || Electrolytic (radial) || 6
|-
| 10&nbsp;µF || 10&nbsp;V || Tantalum || 8
|-
| 47&nbsp;µF || 16&nbsp;V || Electrolytic (radial) || 3
|-
| 47&nbsp;µF || 10&nbsp;V || Electrolytic (axial) || 2
|-
| 100&nbsp;µF || 25&nbsp;V || Electrolytic (radial) || 2
|-
| 220&nbsp;µF || 16&nbsp;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 containing mains-side suppression capacitors and bulk smoothing electrolytics (output 5&nbsp;V at up to 4.4&nbsp;A, 22&nbsp;W; ripple should be within 50&nbsp;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''' &mdash; 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&nbsp;V with a meter''' before touching the primary side, then replace the electrolytics and any cracked mains-suppression (RIFA-style) capacitor &mdash; 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 ==

# Reassemble; reconnect the mains lead.
# Power on and confirm RISC OS reaches the desktop.
# Measure the +5&nbsp;V rail (4.9&ndash;5.1&nbsp;V) and check ripple is within 50&nbsp;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]]