Removed microwave from enclosure and removed cover, hoping it was as simple as a blown fuse. Found extremely helpful diagnostic sheet thoughtfully provided by manufacturer in an envelope affixed to top of cavity. Fuse was fine, but tracing the power feed into the machine revealed that the oven cavity thermostat was open--no continuity across it, and the diagnostic sheet indicated that it was non-resettable. Verified the issue by temporarily by-passing the blown thermostat to ascertain that the front panel display got power. It took longer to get the screws for the cover and enclosure back on than it did to replace the thermostat, once I received the replacement part. Microwave works just fine now, thanks!
Fortunately, my brother-in-law suggested it might be the "cut out" switch. After unplugging the microwave, I opened it up and identified one of two cut outs and removed the wires from each side of the cut out. To test if that was the problem, I connected the two wires together, bypassing the cut out. When I plugged the unit back into the wall socket, the lights came back on, and i ran the microwave for a few seconds. It verified that this was the problem. I ordered the part and when it arrived, I removed it with a philips screw driver and replaced it with the new one. I replaced the screw, buttoned the unit back up, plugged it in, and saved a few hundred bucks on a replacement microwave, and as important, saved our landfills and planet a tiny but.
Took the cabinet off the microwave and checked for a fuse. Found that it was good, then checked for the voltage path to the controls and found the cavity thermal cut out was not conducting. Using a voltage meter to check things. Unplug the microwave for several of the tests. You must know how to work with electricity to do this. Installed the new part and the microwave now works. As a hint to what had happened my wife had heated a large casserole then right after that went to heat a smaller dish. At that time the microwave was hot and did not restart.
