My wife told me that she accidentally ran the unit empty for about 20 minutes and it cut off. This led me to hope that it was just a fuse that was blown.
I uninstalled the unit and opened it up. (Not plugged in!) I found the fuse and it appeared to be good. Unfortunately, my meter wasn't working properly. I then went on-line and did some research and came to the conclusion that one of the protector sensors had cut out.
Again, no functioning meter so I couldn't test continuity on the various sensors.. I used a bit of copper wire as a jumper in place of the various cutoff components. I unplugged the AC power, put my wire jumper in place of one sensor at a time and plugged in the unit.
When I got to the overheat sensor the unit powered up when I plugged it in. Eureka! I unplugged the microwave and set about locating the part.
That led me to APP.
Ordered the part, installed it when it came in and tested it. Everything worked so I reinstalled it.
This part saved me about $300 in microwave replacement costs.
I do NOT recommend using my method with the jumper wire. It was expedient and I'm somewhat comfortable around electronics.