Recap guide
Recap the Osborne 1
The Astec power supply has three paper line-filter caps that blow and smoke, so do those first.
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.
- Osborne 1 Astec supply (Medium confidence). How to tell: Astec supply; the Osborne 1 and 1a both fail with RIFA style safety caps. Capacitors: ACMS forum list: C1, C2, C11 0.01 to 0.1uF 250V class X; C6, C7 100uF 250V; C8 220uF 10V; C15 to C17 1000uF 25V; C18, C19 330uF 16V; C20 470uF 25V; C21 2200uF 16V. 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.
- Blown filter caps (High confidence). Two write-ups report blown paper line-filter caps. One names C1, C2 and C11 (0.01 uF and 0.1 uF 250V AC), and the other found two rice-paper caps destroyed. Source
- Power supply electrolytics (Medium confidence). A restoration thread gives a cap list for the Astec supply, including electrolytics, with notes on X versus Y class. 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.
- Story: Smoke from the drive area, then a RAM fault (Medium confidence). An Osborne 1a started smoking about a minute after power-on because two RF paper caps in the supply blew, and three were replaced. Afterwards garbage on screen turned out to be a bad 4116 DRAM found by piggybacking a good chip. Source
- Tip: Cap list and X versus Y class (Medium confidence). A restoration thread on the Astec Osborne 1 supply lists electrolytics from 100uF 250V (C6, C7) up to 2200uF 16V (C21) and X safety caps 0.01uF and 0.1uF 250V at C1, C2 and C11, citing the Console5 wiki. It explains X class is designed to fail shorted and Y class to fail open, so match the class. Source
- Watch out: Slow power-up and a live mains breaker (Low confidence). An Osborne 1 restorer found cracked X2 filter caps and replaced all the electrolytic and paper foil caps, then powered up slowly from a bench supply through a 120 ohm 5W resistor. He noted the thermal breaker in the mains path is a live hazard and the schematic misrepresents the +5V and +12V distribution. 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.
- Osborne 1 (Write-up) by DOS Days. Has a capacitor list. Blown filter caps and the replacements chosen
- Osborne 1 - Restoration (Forum) by ACMS forum. Has a capacitor list. Cap list for the Astec PSU including electrolytics, with X vs Y class notes
- Repairs to an old Osborne 1a (Write-up) by Terry Stewart (Classic Computers NZ). Two rice-paper caps destroyed; no values
- Fixing a TRS-80 or Osborne Power Supply (Write-up) by trs-80.com. Has a capacitor list. Short X2 replacement values
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.