Maybe time to give up!
Yesterday I replaced the 750mA fuse, put a bowl of water in and turned on the microwave, it appeared to start as usual then something popped. I figured the fuse.
Looking tonight and the 750mA fuse has not in fact blown. Then, although it tested OK the capacitor appeared a bit swollen. It was 1.14uF.
Figuring nothing to lose, I replaced the cap with a good, brand new 1uF capacitor.
Plugged in and nothing. Now not even the screen lights up.