Question about Microwave Ovens
A microwave can be dead for many reasons.
If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.
Then when it cools, it closes the circuit and allows power through again.
If it's intermittent or random, it may be a bad connection, usually on the control board or a loose fuse holder, or even an intermittent fuse.
You should do a continuity test the fuse while it's in the holder (with the microwave unplugged, of course) then turn the fuse by hand or take it out and put it back in, then test it again. If you remove the fuse, then press the meter leads against the ends, it can allow internal contact to be made and make a bad fuse appear to be good.
If it went dead almost immediately after pressing the Start pad, that's usually a shorted high-voltage capacitor.
If it went dead a few seconds after pressing the Start pad, that's usually a failing high-voltage transformer.
If it goes dead or blows the breaker when you plug it in or open or close the door, then there's a problem with a door switch or door switch mount.
If the fuse is good, it may be an open thermostat or thermal cutout on or near the magnetron or on top of the cavity / body of the oven. If it has a hood thermostat, that should read open, as opposed to the others, which should read closed.
If you or someone you know decide to look into it, we have critical safety information and disassembly information at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk
We're happy to help and we appreciate your thoughtful rating of our answer.
William E. Miller, AS-EET
Posted on Apr 18, 2008
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