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Re: HELP! Altair 8800B blew smoke!

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  • horacehall
    ... check before the next ... It is common for old electolytic capacitors to fail if hit with rated voltage after long storage. The electrolytic barrier needs
    Message 1 of 4 , Jul 22, 2003
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      --- In altaircomputerclub@yahoogroups.com, "stevenaleach"
      <leachm003@h...> wrote:

      > Capacitor C4 on a voltage regulator VR1 is fried... crispy.. charcoal..
      > Also, assuming I can replace this, any suggestions of things to
      check before the next
      > attempt?

      It is common for old electolytic capacitors to fail if hit with rated
      voltage after long storage. The electrolytic barrier needs to be
      reformed before it is put into service. This is a big problem with old
      radios, TVs, etc., and the Altair should be no exception. If possible,
      just replace the cap. If you want to do it the hard way, to keep
      original parts, you need to 'reform' the cap.

      To reform the cap, connect it to a source of variable voltage, and
      slowly raise the voltage from zero (or close to it) to the working
      voltage. Preferably, if you have a meter, monitor the current through
      the cap to see that it doesn't get too high. Alternatively, see that
      the cap doesn't start warming up. If watching the current, you should
      see it rise with increased voltage, then over a span of time it will
      drop off. The idea is to get up to working voltage while keeping the
      current low. At working voltage, the current should eventually go to
      nearly zero after a while. If not, replace the cap.
      --Wayne
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