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Recap guide

Recap the Acorn Archimedes

The bigger risks are the soldered NiCd battery and a shorting 12V tantalum, though early supplies can have RIFA caps too.

Open the interactive checklist Tick off each capacitor as you replace it. It saves in your browser.

Check first. A recap is not always the answer here, so look at the guides before you order parts.

Which board do I have?

Boards changed during production. These notes come from the linked sources, and many are only partly documented, so check the board in front of you.

  • A300 and A400 series (Medium confidence). How to tell: Early models with off board AA battery cells. Capacitors: Tantalum 12V decoupling cap C37, 100uF 16V, fails short; fit 100uF 25V. Capacitor list differs from other revisions: yes. Source
  • A400/1 series (Medium confidence). How to tell: Off board AA battery cells. Capacitors: Same fault cap is C53 on the board, 100uF 25V. Capacitor list differs from other revisions: yes. Source
  • A540, A3000, A5000, A3010, A3020, A4000 (Medium confidence). How to tell: Soldered rechargeable battery. Capacitors: Battery leak is the main problem; the Buyer's Guide says caps are rarely an issue except the A4, and some A5000 had caps fitted in reverse. Capacitor list differs from other revisions: not known. Source

Where to start

Clues from write-ups and forum threads, not a diagnosis. Low confidence means one thread or one repair; high means several write-ups agree.

  • 12V tantalum and RIFAs (Medium confidence). One common-faults page names a failing 12V tantalum decoupling cap (C37 or C53, by model) and early power supply RIFA X2 caps. Source
  • Caps rarely the problem (Low confidence). A buyer's guide says caps are rarely a problem apart from RIFAs, and that battery leaks are common. Source

Tips, tales and maybes

Found in write-ups and forum threads. These are other people's reports, not tested by us. Check part references and values against your own board.

  • Tip: Dead-looking A300/A400 from one decoupling cap (Medium confidence). A seller's fault guide says a faulty decoupling cap can make an A300/A400 look lifeless (C37, 100uF 16V on the A300/A400 series; C53, 100uF 25V on the A400/1). Their test is to remove the suspect cap and power up, and they suggest fitting a 100uF 25V part on all affected models. Source
  • Watch out: Battery leak outranks capacitors on later machines (Medium confidence). An A3000 restoration was driven by a leaking NiCd battery that damaged traces, vias and sockets, with symptoms like no keyboard present and a CMOS RAM error. The author still replaced the radial electrolytics (6x 220uF/16V, 2x 100uF/25V, 4x 47uF/25V, 8x 10uF/16V, 1x 4.7uF/63V) but says the list can differ between board revisions. Source
  • Tip: Do not power up a machine with battery damage (Low confidence). A repairer advises not applying power to a suspected battery-damaged Archimedes until it has been repaired, to avoid frying something that would have survived. The same A3000 had C15 rattling loose and needed top-side soldering. Source
  • Watch out: Assume battery damage; odd cap faults (Medium confidence). ArcWiki's buyer's guide says any battery not already removed will have leaked, usually destroying the CMOS RAM chip, except on 300-series, 440 and 400/1 machines with off-board cells. It adds that A4s need a recap, some A5000s had electrolytics fitted backwards, a RiscPC VCO cap can cause wobbly video, and early supplies with RIFA X2 caps should be replaced. Source
  • Story: A5000 caps about half bad (Medium confidence). An A5000 restoration ESR-tested its caps and found about half bad, some open circuit, with leakage in the audio area and broken traces under the pads. A new CMOS chip also cured other odd behaviour. Source

Before you start

  • Boards changed during production. Check your board number against the guides before you order parts.
  • A mains power supply can hold a dangerous charge. If you are not trained to work on one, have a professional do it.

Guides we used

This page and the interactive bench are built from these. They have the photos and the full detail, so please read them and support their authors.

The capacitor list

We have not checked a capacitor list for this machine yet, so none is shown. Follow the guide above for your board, then add the capacitors in the interactive checklist and it builds a shopping list for you.

Skip the sourcing

While you are in there

Affiliate links. As an Amazon Associate I earn from qualifying purchases. These links only search by name. Disclosure

Steps, tools and safety

The steps, the tools in top, middle and budget picks, and the safety list are the same for every machine, so they live on one page: How to recap, step by step.

Values are shown as published in the guides above, and boards changed during production. Check the board in front of you. A recap involves hot tools and, on some machines, dangerous voltages. You do it at your own risk.

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