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Recap guide

Recap the Sinclair QL

Owners generally report the QL's own board capacitors lasting well, so the usual trouble is elsewhere: the keyboard membrane, microdrives, the plug-in power supply and the hard-working 7805 regulator. The exception reported is US-market boards, where one supply capacitor near the right microdrive connector has failed.

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.

Where to start

We did not find a clear list of what fails first on this machine, so we are not guessing. Read the guides below, check the board for leaks, and replace what you can see.

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: US boards: C42 and neighbours (Medium confidence). One experienced repairer reports two failed supply capacitors on US QLs, both C42 above the right microdrive connector. As a precaution he replaces the seven capacitors in that area plus C4 (between the ROM port and the 8302). Others in the thread say UK boards have given far less trouble. Source
  • Tip: Membrane first, caps rarely (Medium confidence). A veteran says he has never had a failed capacitor in a QL (the design leans on tantalum and ceramic decoupling) but that an original keyboard membrane is very likely dead. His pre-use checklist: 7805 firmly on its heatsink, PSU electrolytic tops flat and dry, no bent expansion pins, chips seated. Source
  • Tip: Regulator at its limit (Low confidence). A museum-style write-up of a restored QL notes the 7805 runs at its load limit and needs a big heatsink or a DC/DC converter. The same page records a brittle original membrane, a worn left microdrive bearing and a replaced mains plug. Source
  • Watch out: Test a PSU under load (Low confidence). In a thread about a homemade supply, posters note the 7805 needs roughly 7V at its input to make 5V, and that a supply reading fine unloaded can sag under load. Advice was to load-test with a bulb rather than risk the QL. Source
  • Story: Lost 15V AC was a transformer winding (Low confidence). One QL supply lost its 15V AC output while the 9V DC side still worked. The owner traced it to a degraded transformer secondary rather than a failed part. A reminder that the original wall-wart style supplies age too. Source
  • Story: Buzzing PSU, half-synced display (Low confidence). A QL owner with a buzzing supply on one machine and a display that would not sync on the bottom half on another was told the 9V DC side was probably collapsing under load. They gave up on the originals and bought a modern replacement supply. 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

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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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