Larry,

The best way to isolate the problem is to first do a System Reset by pressing Function/Utility/System Reset, then be sure that all the boxes on the lower left corner of the display are checked, and press FACTORY RESET EXECUTE and finally YES.

CAUTION: THIS WILL WIPE OUT ALL INFORMATION STORED IN THE KEYBOARD'S ONBOARD MEMORY. BE SURE TO BACK ALL YOUR REGISTRATIONS, MFD, ETC.., UP ON YOUR USB DRIVE BEFORE DOING A FACTORY RESET. AND JUST TO BE ON THE SAFE SIDE, REMOVE THE USB DRIVE AFTER PERFORMING THE BACKUP.

If the problem persists, the next step would be to open the keyboard, then carefully disconnect and reconnect each of the plugs going to the various circuit boards. If there's a loose connection, which sometimes happens when the keyboard is constantly being transported and jarred around, this often solves the problem. While all of the connectors are lock-type connectors, sometimes the locking latch is not fully engaged.

If there's a cold solder joint or a hairline crack in one of the circuit boards, the problem is nearly impossible to diagnose and find. I only know of one individual in the United States that is good at this and he is located in Westminster, Maryland. He is one of the few techs that will actually replace defective parts on a circuit board instead of replacing the entire board. He is in very high demand and every independent music store in the area relies heavily on his expertise and services.

Good Luck,

Gary