Yamaha Cvp 303 Clavinova Problem

by Dennis
(Richmond, BC Canada)

My Yamaha cvp 303 has many functions I do not use, ie direct access button and others around the display.

One day I must have accidentally pressed one of these which caused it only to play in grand piano.
3 times after, I managed to turn the functions back on by placing a sheet of paper over the display area and pressing around with my hand, in a short time all functions restored.
I find it not affordable to truck the piano to a repair shop as no place is within 30 miles away, and do not make house calls.
Is there any way to check immediately which button is the cause, as I have to experiment and wait as per previous, with out knowing which one caused the problem. I have the circuit manual but don't know if that is necessary.
I would be very happy if someone knows of a way to check which switch it is, as the processor seems to be fine.
Dennis@sewgrand.com