I just recently acquired a 1994 Mark II and it also has the PWM OVER fault code, and will not even play a note. The control system and display panel work fine.I obtained a copy of the service manual which shows how to do an easy diagnostic check of all the error codes stored on the system. (just like a car) You can read the codes and the number of instances each fault code was triggered. Anyway, it pointed to the power supply, as others have pointed out. I have an upright, so I removed the lower panel and the power supply is right there. I instantly noticed a bulging capacitor and leaking fluid, so that tells me the power supply either needs to be replaced or rebuilt. My local piano dealer is sourcing one from Japan, but I am certain it can be rebuilt easily stateside, with new components to replace the aging ones.