Try doing a factory reset...Pg 31 in the Owner's Manual.
You can also reset a specified setting to the factory default value.
Call up the operation display: [FUNCTION]  [I] UTILITY  TAB [E][F] SYSTEM RESET.
For details, refer to the Reference Manual.
Hopefully, this will fix your problem.
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.