@paulabridge I just went through a similar situation with my son's microwave. In that case it turned out to be a case where the position of two of the switches got reversed so the sequencing was now wrong and causing the fuse to blow when the door was opened while running.
[post|801933|SOLVED: Fuse blows when opened during heating - Microwave Oven Frigidaire - iFixit|new_window=true]
I would suggest you look carefully at the sequencing. One switch will generally open before the others, so you'll need to check the switches themselves for any kind of gummy residues that could be causing them to operate slowly or check the mechanical parts that activate the switches for worn or bent parts that would again allow the switches to work out of sequence.