Hi Jim,
My microwave stopped working. I don't recall if it finally blew the fuse, but it was arcing behind the control panel. Being an electrical engineering, I investigated the circuit as you and other have suggested. Nothing seemed to be amiss.
It turned out that the little microwave transparent window in the back upper right of the unit had food splashed on it. The dirty window was not allowing the microwave energy to get into the enclosure. As a result the energy found another path and caused the arcing.
A $4 replacement window from Amazon solved the problem.
Dave
PS, my wife wanted to just throw it out and buy a new one, but like many here, the reward of fixing something outweighs the financial consideration of the time spent on the repair.
