Ours didn't work when we bought the moho. I priced new units but would have sacrificed an exhaust fan and overhead light . . . or spent $500. Ended up figuring out which board to replace and ordered from a repair board shop. Didn't even have to drop the unit from it's mount (it dropped on it's own late last year). Still working today.
Somebody dropped a cheap uwave outside my office, non-working. Replaced the fuse inside. Still working today.
If you have the money, by all means buy a new one. If you don't have the money see if you can fix it yourself. You don't need an engineering degree or head up an engineering dept., just get creative, look inside and search on-line for repair parts.
Best,
- bob