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5454Re: [midatlanticretro] WTD: Morrow Wunderbuss Thinker Toys Motherboard Schematic/docs

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  • Dan
    May 7, 2007
      I almost posted a lengthly explanation on the march group list before I
      noticed you posted the pic on cctech. The power supply in that circuit
      is a -12V not +12V. The voltage regulator part # on there is a 7912
      which outputs -12V. The part that is blown on there is an electrolytic
      cap, not a zener (note the + sign on each end of the cap). Both of those
      parts below the 7912 are the same type of part.

      Caps always dry up and blowout--they don't last forever. That's why it's
      good to have a Variac when powering equipment that hasn't been on for a
      long time--a homemade current limiter helps too if no variac is available.

      But I'm not sure of the value, it can't be very high in value, possibly
      only 3.3uf or 4.7uf considering the size, this isn't very critical , so
      long as you keep it in the ballpark. The caps for the 7805 regulator on
      there beside it are only 2.7uf. I would suggest changing both of them,
      for sanity's sake--they both might be damaged.

      The other important issue is to check the traces for damages when you
      remove the bad parts. They could have burned through creating an open
      circuit. So you'll have to splice the traces back together if this is
      the case. Some skinny telephone copper wire always does the trick. And
      last but not least, is the 7912 voltage regulator. You should check the
      -12V power before you plug in any cards.


      [ My Corner of Cyberspace http://ragooman.home.comcast.net/ ]

      B. Degnan wrote:
      > Herb/Anyone else..
      > I have a 1977 Morrow Wunderbuss "Thinker Toys" S-100 Motherboard with a
      > blown Zener diode near a 12+V position at the back of the board. Anyone
      > have a schematic? I checked Herb Johnson's site, there is nothing for
      > this
      > board listed. I would like to determine the exact type of diode so I can
      > replace it.
      > What would cause a Zener diode to pop?
      > Thanks.
      > Bill
      > _
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