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Posted on May 15, 2009
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Panasonic NNA554W blows 10a fuse when microwave comes on

There was a bang in the middle of the night and found 10A fuse blown in microwave in morning. Replaced it and timer came on ok but as soon as microwave powered up fuse blew again. What are the most likely candidates for causing this problem?

  • m_charleston May 15, 2009

    Thanks for the pointers, no problems with servicng microwaves been electronics engineer nearly 40 years but find it hard to get data and parts for some jobs due to franchising etc. Thanks for the help, really appreciated, as I can't find any charred components or shorts on pcb's and no circuit diagram ... and what was wrong with the old reliable analogue psu to the Magnetron, made good boat anchors when broken.

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  • Master 2,992 Answers
  • Posted on May 15, 2009
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Possibly the interlock monitor switch is bad or out of adjustment. This switch is designed to create a short circuit across the power line (and then blow the fuse) if you attempt to defeat the door interlock and operate the oven with the door open. A shorted capacitor or diode could also cause the fuse to blow. Because of lethal voltages inside and the possibility of microwave leakage if repairs aren't done correctly, you are best off leaving microwave service to professionals.

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