SOLVED!

The error stemmed from a loose CPU chip on the motherboard. I took off the bottom of the keyboard and there it was, right in front of me - a big Korg 64-voice chip on a sisterboard. I pushed the board into its socket and it held securely. Problem solved. The board goes back to Florida tomorrow.
Whew!!!
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Riding on the Avenue of Time
cassp50@gmail.com