Yamaha GSX-640 dual function appearing unrequested

by Filip Neuls
(Czech Republic)

I have a problem with my Yamaha GSX-640 keyboard. I am not able to switch off the DUAL function appearing unrequested. To explain:

1) When I switch on the keyboard, there is automatically 001 Live! Grand Piano set from the start (no dual voice).

2) When I move the dial wheel counting up (clockwise, i.e. 002, 003, 004 etc.), it is all OK, no dual function appears.

3) But when I move the dial counting from 001 down (counterclockwise, i.e. 000, 535, 534 etc.), the dual function appears automatically and stays all the way, no matter of subsequently selected main voice or turning the dial wheel up and down so I always have to switch it off manually (by the 'dual' button).

It did not work this way when the keyboard was new. The dual function came only when I wanted it. So please, is there any chance how to fix this problem? Reset to factory settings (main switch ON + holding the highest white key) does not work. I know that I can avoid the problem simply not using the dial wheel, however, I feel that this is not the standard method. There is something wrong set in the 000 position (OTS) and I am not able to change it. The dual appears everytime I pass the 000 position when spinning the wheel.

Thank you for your help!