How to access the DX7s internal diagnostics
The Yamaha DX7s internal diagnostics can be accessed as follows:
Switch the DX7s on.
Press the 'EDIT' button, '16' button and '32' button simultaneously. The easiest way to do this is to press the 'EDIT' button with one finger of your left hand and keep it pressed; then press the '32' button with one finger of your right hand and keep it pressed too; finally press the '16' button with a second finger of your right hand, then release all buttons.
TEST V1.1 87.04
BATTERY 2.9v OK
The resulting display shows the diagnostic test version, current internal battery voltage and status. To exit the diagnostics and return the DX7s to 'normal' mode, press the 'VOICE' button.