Microwave was emitting a burning smell but operating normal. Next day it quit heating but everything else worked normal, no unusual sounds. Pulled it out and found the Thermostat on the side of the Magnetron burnt and seperated. My question is, what could cause this and what should I check for? I have parts ordered for what obviously is wrong, but what could have led to this failure? I would be happy to hear this could be the only problem due to age of the thermostat.
This thermostat is actually thermal fuse. It protects the microwave from overheating. So, the problem can be a bad cooling fan or a bad magnetron.
Check the cooling fan motor by measuring the resistance between its terminals. The normal reading should be about 25 Ohms.
If the motor is good then most likely the magnetron itself is bad.
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Gene.
Thanks Gene. Would you suspect the Magnetron even if it was working in all modes, then suddenly quit? The Thermal fuse was burnt so badly, the spade connector from the transformer was burnt to the connector and the downstream spade connector was completely burnt off. The insulator over the thermal fuse was melted, yet there was no heat damage to the metal exterior of the Magnetron where the thermal fuse mounts directly to.
Check the cooling fan motor. If the magnetron was not exposed to the high heat for a long time then there is a small chance that it is not damaged. There are no reliable instrumental tests for magnetrons.
Replace the the thermal fuse and run the microwave. Hopefully it will work.
Gene.