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Recap guide

Recap the TRS-80 Model I to 4

The classic failure is the paper-style X2 line-filter caps in the power supply, and swapping them is cheap preventive work.

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.

  • TRS-80 Models III, 4 and 4P (Astec supplies) (Medium confidence). How to tell: These models typically use one or more Astec supplies. Capacitors: Failure is the X input caps: a large 0.1uF 275VAC X2 and a small 0.01uF 275VAC X2. Capacitor list differs from other revisions: not known. Source
  • Model I external AC adapter (Low confidence). How to tell: Model I uses an external adapter containing the transformer; the supply makes 12V, 5V and -5V. Capacitors: The write-up describes voltages and fuse only, not capacitor values. 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.

  • Line-filter caps (Low confidence). A Model III/4 repair article gives two film cap values, 0.1 uF and 0.01 uF X2 mains caps, though its author marks it as unverified. Source
  • Model I supply (Low confidence). A Model I supply page lists component designators but does not say which parts fail. 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: Model III/4 supply fails at the X2 caps (Medium confidence). The page describes the failure as a loud pop and smoke from the metalized film line caps, usually the larger one first. It lists 0.1 uF and 0.01 uF 275VAC X2 replacements and says to get the right X rating for fire safety, with a note that it is unverified. Source
  • Story: Expect dormant filter caps to blow (Low confidence). A poster said the filter caps on dormant TRS-80s blew within about a minute of first power-up, and one supply was still smoking half an hour after unplugging. The advice was to replace similar caps proactively; values mentioned were 0.1, 0.01 and 0.47 uF X series. Source
  • Tip: Replace the whole mains filter group (Low confidence). In a TRS-80 smoke thread, a veteran repairer said smell and smoke while the machine keeps running point to a mains filter cap, usually among the lowest-numbered caps (he guessed C103 here). His habit is to replace all of the filter caps, the X class across the mains and the Y class to ground. Source
  • Story: Model 4 recap: backwards PSU cap, and C322 must be non-polarised (Medium confidence). A Model 4 owner recapping the video board received a much smaller replacement for C322 (10uF 25V non-polarised, in the horizontal circuit before the yoke) and was told the part must be non-polarised. The real fault was a cap fitted backwards in the supply, which gave a dimmed, shrunken screen and smoke; the failed cap showed tiny pinholes in its corners. Source
  • Tip: Where the X2 caps sit and run it loaded (Medium confidence). A TRS-80 repair page locates the 0.1uF and 0.01uF 275VAC X2 caps on Astec Model III/4 supplies and gives C1, C2 and C13 (Astec) or C32 and C33 (Tandy) for the 4P. It stresses switching supplies must be tested with a load or the voltages read well out of spec, and that the advice is unverified suggestions. 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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