Thanks for the suggestions.
Didn't see any fuses but I can put my meter on the door switches.
I realize Dometic / LG doesn't have the best reputation but it worked fine for 11 years. I'm not going to fool with the microwave generator - my life is worth to much (to me anyway) but that appears to be working (there's a combination of buttons that will start it in a useless way (but it works) - just not with the start button.
Incidentally, if the microwave works in this 'odd mode' I'm guessing that means the door switches are working.
Do you think the refurb LG board on ebay is compatible?