Strange problem with KR-4700

[rjgarment]

I have a Roland KR-4700 that has a strange problem. Certain C and E keys won't work. It alternates octaves, so one octave all keys except the C work, and the next octave all keys except the E key work. Next octave C doesn't work, next octave E doesn't work, and so on and so forth. It's the same with all instruments, and I've tried doing a factory reset to no avail. Any ideas what the problem could be? Any advice would be greatly appreciated. Thanks!