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.