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Microwave problem

Discussion in 'Electronic Repair' started by [email protected], Dec 24, 2004.

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  1. Guest

    Our 20 year old (1984) JC Penney microwave, model 5919-00-40, ceased to
    work last night. It acted like the fuse had blown, which it had, but
    that didn't cure the problem. Further investigation revaled that the
    problem lies in the control pad, not the actual part that does the
    cooking and can kill you. I took out the circuit board, which contains
    the display, keypad, etc. and controls the microwave, and looked it
    over to see if there were any obvious problems, such as another blown
    fuse, which there weren't. I saw some little strips of wire on the
    board in various places marked 9V, 12V, etc. and when I connected a
    meter between them and the ground wire I got no reading. I verified
    that the transformer was providing electricity to the board, and the
    output frpm the connectors matched the values printed on the circuit

    By accident I shorted out part of the transformer for the board, the
    10v section, and to my surprise the display lit up and the buzzer
    beeped, like it would after a power failure. Then it would sort of
    slowly fade out. I didn't repeat this too many times because I didn't
    want to ruin the power transformer or anything.
    want to scrap this as it is so simple to repair, as far as the layout


  2. You say you measured the outputs of the transformer? So, the 10 V output
    measured 10 VAC

    Also, you said a fuse actually did blow?

    The circuitry between the transformer and the DC outputs should be quite
    simple. If you aren't getting any DC voltages at, something is likely
    open - a bad solder joint or fusable resistor.

    The effect you describe of shorting the 10 VAC output from the transformer
    sounds strange. Possibly you were pushing on something in the vicinity
    and the act of shorting having an effect was just a coincidence.

    I could speculate but better to just trace the circuit for one of the DC
    outputs and check each component and the wiring. It shouldn't be too hard
    to find the problem now that you know the rest of the circuit probably works.

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  3. Tim R.

    Tim R. Guest

    First off, the name I used to post this question is the one I used when not
    at home, so please don't be confused if the name on this message is
    different than that of the first.

    The main one did.
    That's probably it. I'll spend an afternoon working on it.
    I shorted the ground of the circuit board and a lead from the transformer
    that was directly connected to a fuse of the circuit board, not the main pwr
    supply fuse, and that produced the effect described. I thought the same as
    you - that it might be a nearby component - but repeated shorting confirmed
    that indeed one part of the transformer was being shorted.
    Yes. Shouldn't be too difficult
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