OP

Quoted from TimeBandit:

Well, this was a surprise. WoZ just sitting in the basement on attract mode, like any other night. I was at the bench out of field of view, and could smell something. Turned around to see a few inches of smoke collecting at the ceiling. Popped round the corner to find WoZ dead. No screen or inserts. The lights on the headphone jack were still on. There was no smoke visibly coming out of the machine. I turned it off and opened it up to see what melted. Nothing. No evidence of any damage anywhere.
So I guess something has burned up and has to be replaced, but I have no idea where to start looking. All fuses seem good, with all the status LEDs on when it's powered up. No more smoke is being generated when I turn it on so whatever burned has finished burning.
In summary, board status LEDs all look on, headphone jack lights on. Inserts off, screen off, fans off.
I just can't believe there would be that much smoke and no evidence of any burning. Weird. Any thoughts?