Yamaha CVP 55 no sound from keys?

by Gene
(Kent, UK)

Hi All,

I have a Yamaha CVP 55 which turns on and plays the demos and even plays beats, however when I press the keys none of them seem to create any sound? I got the piano from a friend who said that his friend opened it up and played with a few wires, after putting it back together the keys weren't working.

I have opened it up and followed instructions to take out the keyboard unit but couldn't see any issues. Any help offered would be greatly appreciated.