Recap guide

Recap the BBC Micro and Master

The original RIFA X2 caps in the power supply are known to go pop, and the starter electrolytic is stressed too. Cheap kits exist.

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

Worth a recap. Reports say it is a common and useful fix on this machine.

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.

Astec supply (Model B) (Low confidence). How to tell: Maker name shown on the supply. Capacitors: A UK kit lists C2 100nF X2 x2, C1 10nF X2 x2 and C9 220uF 25V 105C for all supplies it covers. Capacitor list differs from other revisions: no. Source
BSR supply (Model B) (Low confidence). How to tell: Maker name shown on the supply. Capacitors: Same single kit listed. Capacitor list differs from other revisions: no. Source
Hitron supply (Master) (Low confidence). How to tell: Maker name shown on the supply. Capacitors: Same single kit listed. Capacitor list differs from other revisions: no. 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.

X2 line-filter caps (High confidence). Several sources point at the two PSU X2 caps (100 nF and 10 nF) as the ones to replace. Source
Starter electrolytic (High confidence). Kit and how-to pages name the 220 uF 25V electrolytic C9 as the other power supply part to replace. 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.

Watch out: Warning signs of the X2 caps (Medium confidence). A kit seller lists an acrid smell, hairline cracks or split resin on the X2 caps as signs of imminent failure, and says the caps are only noise suppression, so the machine runs without them. It cites a 100nF and a 10nF part. Source
Story: Cracked Rifa caps on arrival (Low confidence). One restoration found both Rifa suppression caps cracked and the small one slightly bulging, and the author says near-40-year-old ones rarely last long once powered. The caps were replaced before the first power-up. Source
Tip: Three classic BBC supply faults (Medium confidence). A BBC repair page lists a dry startup cap C9 (220uF 25V 105C, strained sound at switch-on and 5V below 1V), a failed chopper transistor Q2 (BU208A on the B, 2SC2928 on the Master), and smoking X2 caps C2 (100nF) and C1 (10nF), 250VAC, 15mm pitch. It warns the voltages inside are potentially lethal. Source
Tip: Smell tells you which cap (Low confidence). A forum post on a smoking BBC says nasty smoke means the Rifa, while a merely unpleasant smell means a dried-out electrolytic. The owner fixed it with local capacitors and was pointed to a kit seller. 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.

BBC Micro PSU X2 capacitors (Write-up) by Retro-Kit. Has a capacitor list. Explains the failure and the two X2 values
BBC Micro Model A, B and B+ PSU Capacitor Kit (Kit page) by Dataserve Retro. Has a capacitor list. Kit contents by designator, including the C9 electrolytic
BBC Micro Restoration Part 1 (Write-up) by LinuxJedi. Explains the RIFA and starter cap replacement
BBC Micro how-to (Sprow) (Write-up) by Sprow. Has a capacitor list. Index of BBC repair guides including the C9 220 uF 25V fix

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

Ready-made kit: Amazon · eBay
Already recapped: Amazon · eBay

While you are in there

Need the machine itself?: Amazon · eBay
A box of spare capacitors: Amazon · eBay

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.