Gary sounds like he has the right solution, I guess I was trying to say was it was probably a loose connector.
The other board I refered to was an old ensoniq and the factory explaination was there was three circuit boards and ...well you know the rest, they no longer make keyboards (that I know of).
But we had the same frustration of going to many techs, many times, for over a year until someone discovered the problem.

Good luck and let us know how you make out.