Samsung Model ME21F707MJT Over the Range Microwave built in July 2013.

It was working until trying to heat something caused it to completely shut off after a few seconds. I unplugged and tested the door switches and thermal switches. All NC and NO switches were testing OK. The two ceramic fuses have continuity.

After removing the PCB control board and then reconnecting everything, the microwave turned on and I was able to get it to heat something for about 1 minute before it turned off and reset the display, asking to have the clock set.

Then, roughly 4 out of 5 times trying to heat something, the display resets and asks for clock reset. 1 out of 5 times, the display turns off and does not come back on at all until unplugged for a while and plugged back in.

Today I used it successfully for 4 minutes of total heat time over several stops and starts as long as 2 minutes with no issues.

How can I isolate and repair this intermittent problem?

Maybe relevant: one of the two ceramic fuses has a discoloration like a faint line around the center. It might have been printed, or maybe is a failure indicator. But the fuse tests good for continuity and I don't have any replacements to test.

  • how do you know that the problem is in the microwave? – jsotola Feb 13 at 22:42
  • I am not having any problems with other appliances. The microwave is on it's own 15 amp breaker in a sub-panel. I flipped and reset the breaker manually during troubleshooting and that didn't change the behavior. I can't say 100% that it's the microwave, but I can't think of how it could be the power source in this case. – shanemgrey Feb 13 at 22:45
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    if you are having problems with an electrical appliance, it makes sense to plug it into another outlet to make sure that the problem is not caused by a faulty elecrical outlet, before doing any work on the appliance – jsotola Feb 13 at 22:55
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    Yeah, try with a heavy-duty (12AWG) extension cord to the nearest countertop outlet (coffee mug of tap water, 2 mins on HI). That will tell us if it's an issue with that particular branch circuit at least...also, does the voltage in the house dip when the microwave resets? – ThreePhaseEel Feb 14 at 0:02
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    The voltage in the house does dip when it resets. I can see the lights in the kitchen dim at that time. – shanemgrey Feb 14 at 0:07

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