UPDATE:
It turns out that the cable connection from the piano to the controller has three prongs missing. That should have been the first thing I checked, but for some reason it never occurred to me. So the controller is receiving enough data from the remaining prongs to turn it on and operate some functions, but not enough to work data properly.
My question now is: How do I replace this cable? The other end goes into the amplifier. Is this a simple matter of opening up the amplifier housing, pulling out the bad cable and inserting a good one? Or is it more involved and I should hire a Disklavier technician or electrician?
Dave