Yamaha PSR S710 Selects Tknes Randomly By Itslef

Hello Everyone, please I.have a Yamaha Psr S710 which selects/picks tones & voices by itself randomly. Please what could be the problem?
And what am.i expected to do in repairing it?

Thanks so much.

I am not familiar with the operation of that keyboard, but that sort of problem often indicates a faulty data slider or tact switch. If the slider can be used to change programs, and it is dirty, it will often jump between resistance values when you are not even touching it - and the keyboard interprets this as you telling it to change programs. Similarly, if a tact switch is worn out, it might be dancing on the edge of making contact and not making contact.