van wikipedia:
"To test for dead voices perform the following procedure. Enter diagnostic mode by holding the transpose key down upon power-up. Then, to see which voice paks are bad, push poly 2 key and press keys one by one (any keys), making sure to hold down every key previously pressed. The display will read from 1-6. When you do not hear anything from a key, look at the number on the display. The number displayed is the number of the voice chip that has failed."