We have been having trouble with our refrigerator for months, then suddenly the microwave seems to have caught the bug, too. When the door is open, the turntable now turns when it should be still. Closing the door, happily, causes it to stop.
Some searching on YouTube gave the general diagnosis… one of the switches that opens or closes when the door is open must have failed. The push button on the switch depends on a metal spring, and if the metal fails from repeated opening and closing of the door, the switch is stops working.
After turning off the power, digging into the microwave is the mechanical equivalent of reading someone else’s computer code: there are screws, clips and guide pins everywhere, and it takes some time to see just how to take it all apart and remember how to put it back together.
Eventually, one of the three switches was plucked out, and indeed the button no long made the satisfying “click” when it was pushed. With the part number noted, all was reassembled. A matching switch was quickly found on Amazon, and now we wait for it to come so we can dive into the machine again.