I encountered same problem, and all interlock switches tested o.k. I remembered that problem started after turntable plate was off kilter. After a couple fuses, I decided to disconnect turntable motor - it works now.
Sounds like you may have a bad door switch or misalignment which has blown your internal fuse. If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info (as well as a text file which helps in diagnosing and repairing door switch problems) at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk
If the microwave runs for a few seconds and then shuts off, a door switch might have failed intermittently. Check each of the door switches for any signs of overheating, arcing, or burning. Also check each of them for continuity. Replace any of the switches that is visibly damaged or that only has continuity intermittently
the microwave runs for a few seconds and stops the touchpad and
control panel might be defective. There are several other components
that can cause this problem, be sure to check any other components
before replacing this board.
the microwave runs for a few seconds and stops the touchpad might be
at fault. This is not common. Generally speaking, if the microwave
display is working and some of the buttons respond correctly but
some don't, the problem is with the touchpad.
the microwave runs for a few seconds and stops the thermostat might
be defective. Watch our video on testing thermostat
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