My GE model mc0165uw above range oven blows its 20amp ceramic fuse when i close the microwave oven door. I have checked the continuity of all 4 door interlock switches, and as far as I can tell they check out ok. What would be the next troubleshooting step here before heading to the pawnshop for a new one.
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Years ago I had experience with helping an electronics shop owner next door to my office fix a similar problem. The problem turned out to be alignment of the micro switches which were all on plates with adjustment slider holes. On his unit the door interlock micro switches had an interesting contact arrangement with wiring such that when the switches sequenced incorrectly a direct short would be imposed across the power line through the fuse. This would cause the fuse to blow and render the unit non-operational. Best we could determine it was designed as a safety interlock system. It turns out that we guessed correctly.
It is a requirement that microwaves have an interlock monitoring system to pop the fuse if the switches are not operating correctly. There is a good description here:
http://www.microtechfactoryservice.com/switch.html
Update:
From this more current link:
. there is this text:
WHAT CAUSES A FUSE TO BLOW?
DOOR SWITCH If a fuse blows when the door is closed or opened, it is most likely caused by an issue with a door switch. Microwave ovens typically have three or four-door switches that are designed to cut off the power to the microwave by tripping a fuse if the door is not closed properly. A door switch will usually fail due to wear and tear or because it is stuck. Incorrectly installed door switches can also cause a fuse to blow.
Door switches can be tested with a multimeter for continuity – a continuous electrical path – to determine if they need to be replaced. Make sure to follow the safety warning above before accessing the microwave.
You can access the updated link for a bit more information.
Michael Karas
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