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Tyler Z.
Tyler Z., Appliance Doc
Category: Appliance
Satisfied Customers: 73409
Experience:  9+ years being an appliance technician with factory training.
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My microwave turned on by itself while I was out of the kitchen,

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My microwave turned on by itself while I was out of the kitchen, without the light coming on, and then I started smelling like plastic was burning. When I came to the kitchen, I found out it had no power. About 10 minutes later it came on again by itself, and the light inside the unit turned on again. I left the door open because I think it's going to start again and malfunction. Have you heard of this problem before?
Hello, and thank you for using this service. I'll be helping you with your problem today.

The microwave cutting out means that the magnetron overheated which happens if the microwave turns on without anything inside. If the microwave is turning on without anyone there, then your control board itself would need to be replaced which is about $200 or so to have replaced. It might be better to replace the microwave rather than repair it, but that's completely up to you.
Customer: replied 5 years ago.
How do magnetrons overheat? Is this common? Are magnetrons covered by warranties? This model was built in 2006. How can I uplug it since I'm afraid it's going to turn on again. It's a built in model that fits inside the cabinetry.
Magnetrons overheat from turning on without food inside the microwave. Or if the fan isn't running when the microwave is turned on, that will cause the magnetron to overheat also. The unit will not be under warranty unfortunately. If this is a unit that is built into the cabinet it will probably be worth repairing for sure still, so it sounds like you may need a new control board if it's turning on and overheating on it's own.

Customer: replied 5 years ago.
How much to fix a control board and/or fan and/or magnetron? Should I just leave the door open so that it does not turn on?
If you shut the door does it automatically turn on? If so, put a cup of water inside and see if it heats up. Generally when the unit turns on as soon as the door shuts the microwave is not actually heating. If this is the case, you also have a bad door switch (1 of the 3 door switches has failed).

It really depends on what problem you have, but you're looking at about a minimum of about $200 to fix any problem because these built in units are not easy to access. If you need a control board, that would be the most expensive part and that's about $200 by itself.

Customer: replied 5 years ago.
As soon as I closed the door with the cup of water in it it started to "hum", with no light coming on. The hum does not sound like the regular sound the microwave would make when working. The inside of the microwave was still warm from the last time it had come on by itself.
ok then that sounds like your control board is bad. That humming means that the magnetron is getting power when the door is shut, so leave the door open or turn the circuit breaker off to the oven until you get the control board replaced.

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