Phil,
this is why I suggested to contact Lou in New York. There were many SD1's with the same problem when the keyboard first came out. There is a large circuit board under the display which is connected to the top board by screws. Right in the middle of this board is a smaller board which is connected with a couple of fasteners (not soldered) and it is possible that these connectors come loose. Now, Ketron is soldering these boards in and the problem has been taken care of. You can open up your keyboard, but if you are not sure of what you are doing, I really do suggest sending it to New York.
George Kaye
Kaye's Music Scene
Reseda, California