Repair and disassembly guides for microwave ovens.

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Making loud Hum when not on, but plugged in.

Samsung SMH2117S Microwave started making a loud hum a few days ago, I unplugged it over night and left it, plugged it back in the next day and still a loud hum, the hum stops when you open the door. As soon as you close the door, without pressing any buttons or starting the microwave the hum comes back. I took the microwave down from above the range, removed the cover to try and pin point where the noise is coming from. the hum is coming from the Magnetron. The unit will still heat food, and everything else seems to be working as normal. I don't really feel like it is safe to leave plugged in or even use. I have found a price on a new magnetron for this product for $115.(i live in canada) i have no problem buying a new one and replacing it. But i want to make sure that is the real problem.

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I had a Maytag microwave doing this. The unit was only 4-5 years old. After testing transformers and magnetron and other interior components I traced the problem to the lower door switch. I tightened the screws just inside the door because one was slightly loose. You could not tell this by opening and closing the door only by applying a screw driver to the screw. I tightened it and everything worked the way it should.

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Thanks! Worked for me and took 2 seconds to do for my samsung microwave. I tightened both screws where the latches engage, and it no longer hums now.


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There is a safety switch (thermostat) that is often located just behind the user interface. If there is an issue with the thermostat or connection it can cause a hum in the motor of the fan motor. Give the safety switches a test for continuity. This was the issue with a humming Samsung microwave I just repaired.

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There are three micro-switches on the latch board. When the door is shut, two of them should be closed and one should be open. If the third one fails and remains closed, it creates an unintended circuit loop that causes hum, although not necessarily operation at full power. I replaced all three switches (since the unit had to be opened up anyway) and the problem appears to have been solved. It may be intermittent however, as it did occur once in the past and went away on its own. The current assumption is that it the switch was still the culprit and replacing it should make a lasting repair.

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Jay will be eternally grateful.
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