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Repair and disassembly guides for microwave ovens.

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Why is my microwave making a hissing sound when plugged in?

My microwave fuse blew when I opened the door to interrupt the cycle. After some googling, I decided to replace the switches and the fuse. I got all the correct replacement parts. After I put everything back and plugged it in, it started to make a strange hissing sound. Any ideas why?

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The connection is loose or improper check them once again


Checked so many times and it’s still making the noise. The sound is high pitched and almost inaudible.


I’ve had a quick look into this, and it seems that the part that is causing the loud noise is called the magnetron tube. This part is what is responsible for cooking/heating whatever is in the microwave, using electromagnetic waves. If the magnetron tube is burning out or failing, it will often create a loud high pitch sound, as the frequencies being produced are higher than what they should be. If you want it fixed, you’ll have to get a professional out to replace it.


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A loud pitch hissing sound is common in capacitors in any device. When a capacitor fails the liquid dialectric will hiss out and the capacitor will swell. A microwave can not run on 120 volts at 20 amps very well so the capacitor charges like a temp battery then discharges into the magnatron to cook the food. Microwaves have capacitors as high as 10000 volts at a low amperage. High amperage would require wires the size of a few fingers to move the power but high voltage does not. The capacitor will hold less and less power till it is not discharging at all and your food will not cook. Unless your microwave is fancy it is not worth fixing and the capacitor is not a DIY item due to the ability for a capacitor that size to throw you across the room with more force than an angry gorilla. Tube TVs used 2000 or so volt capacitors and my grandfather still hit the wall on the other side of the living room from it. I have been interested in electricity ever since.

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