My Fox II 286 mainboard just blew a capacitor. I haven't yet powered it on, so maybe the cap was bad. How can I diagnose this problem, and eliminate other bad caps?

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1 Answer 1


The wear of solid electrolyte tantal caps as these are is neglectable. They are however extremely sensitive to overvoltage. As this is a cap right near the power connector, I suspect the power supply is broken.

This seems to be the +12V or -12V line. Check these on the power supply before reconnecting. Maybe you are lucky and nothing else got fried.

(Chances you accidentally mixed up the two halves of the power connector? What you have there at the back of the photo also doesn't seem to belong to an AT power supply.)

  • I am using an ATX2AT connector with a brand new modular ATX power supply. I put the black grounds in the middle. The supply works with another vintage mainboard.
    – Arne
    Commented May 13, 2018 at 12:49
  • I don't see any reason not to power up this old board. That cap isn't strictly required for function.
    – Janka
    Commented May 13, 2018 at 13:02
  • I measured the other tantalum caps now and i see a bunch of them seemingly shorted out
    – Arne
    Commented May 13, 2018 at 13:06
  • @Arne that can be caused just by IC protection (some ICs short circuit pins while powered down to protect from static voltage)
    – Spektre
    Commented May 13, 2018 at 13:10
  • @Spektre but then the cap won't be shorted, or?
    – Arne
    Commented May 13, 2018 at 14:20

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