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Discussion in 'Electronic Repair' started by [email protected], Sep 27, 2007.

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  1. Guest

    i baught an old APPLE - MAC PLUS computer . i pluged it to 230 v ac .
    nothing happened .
    so i opened the cover . i saw the fuse inside it had burst . so i
    changed a onw 5 amp fuse . and i powdered it ON . i saw spark of fire
    in POWDER/SWEEP board . and again the new fuse had burst . i think
    some component had burst too. so please give me an idea to repaire
    it . OR give me the circuit ,so that i can verify it...
  2. James Sweet

    James Sweet Guest

    Isn't 5A a bit large for the fuse? You may have caused further damage by
    installing too large a fuse.

    These are not difficult machines to work on, just use standard switchmode
    power supply troubleshooting procedures to track down defective components.
    You likely have a shorted rectifier or chopper transistor on the input side
    of the power supply. They're notorious for cooking flyback transformers as
  3. Are you sure it was a 230 volt model? If it had been imported from the U.S.
    it was 120 volt only.

    Look for Larry Pina's book "Macintosh Upgrade and Repair Secrets".

    Where are you, I can lend you the tools and books, but I expect you are
    not nearyby.

  4. James Sweet

    James Sweet Guest

    If you have, or know where I can get one of the flybacks for these that
    would be cool, I realized I have a 512 kicking around with a bad one, last
    one I bought was over a decade ago and the place is out of business now.
  5. Andrew

    Andrew Guest

    Many years since I used to fix these.

    But some ideas, BP cap on the video,LM??? chip in the video, GI??? diode
    in the video, Mis-jumped 120v, dead EHT ,(the little ones would blow,
    and were replaced by a physically larger unit that was also used in the
    SE which lasted.These faults were so common that you could buy kits of
    parts to fix them for the 128k,512k,plus and SE, of which I am sure I
    still have a few.

    regards Andrew
  6. The SE flyback transformer also had a built in drain to remove any
    remaining charge on the CRT anode.

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