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I have a very nice over-the-range microwave that died after 6 years of use (or after 8 months of renting to a very messy person). To replace with the same model used would be cost over $250, thus I decided to trouble shoot it.

If i place a cup of water in the microwave everything seems to work, but the water does not get hot.

I verified the mode stirrer rotates freely, and that it's motor actively turns when the microwave is on. The inside of the wave-guide, the motherboard, and the magnetron are surprisingly clean given the state the rest of device was in.

Because the magnetron is the most expensive part in the microwave, I'm a bit hesitant to order one and try swapping it out.

Are their any other parts besides the mode stirrer I should consider testing / replacing before replacing the magnetron?

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2 Answers 2

Somewhere on the magnetron is a thermal fuse or cutoff. When the magnetron gets to hot, it shuts off power to the device. Some of these fuses reset once the device cools, some don't. Sounds like you have one of the later. You can replace the fuse, temp rating is usually written on the device itself. While you're in there, clean the cooling fins on your magnetron with 409 or similar cleaner and a toothbrush. Buildup of kitchen grease on them can make the magnetron run too hot. Also check that the cooling fan, if any, is working, has a free air path, and is pointed at the magnetron fins. When my microwave started cutting out, all it took was a good magnetron cleaning to get it running again. Sounds like your thermal fuse is a one-shot though. You might replace it with a auto-reset version.

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I swapped with another magnetron, but had no luck; I'll hunt for the temperature fuse tomorrow and report back if it's separate. –  virtualxtc Apr 27 at 7:24
I'm having trouble finding the temperature fuse. –  virtualxtc Nov 2 at 22:28
They can look like this: google.com/… –  Wayfaring Stranger Nov 2 at 23:51
But on microwaves I usually find something like this: google.com/… It'll be screwed down somewhere near the magnetron. –  Wayfaring Stranger Nov 2 at 23:52

Sounds like the magnetron is faulty. Remove it and use a multimeter to test between one pin and the body and then also test from the second pin to the body of the magnetron. If there is resistance , change it. They are cheap on eBay . The fuse from the large capacitor to the large transformer is usually blown as well. Good luck

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if you check my comment on Wayfaring's answer back from April, you'll see I swapped out the magnetron and it did not fix the problem. –  virtualxtc Nov 2 at 22:27

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