Yamaha Clavinova CLP560 'out of tune around C5

by Matt
(Australia)

I have a Yamaha CLP560 and it seems to have a tune issue around B5C5, wherein when the b is pressed, it will play normally for 2 strokes, then play sharp, then almost sound the C.
This happens with other keys higher up the keyboard too. Not on the lower registers.

Additionally, when the demo tune Is played, the upper register sounds dreadfully out of tune - flat.
I have tried the various resets - holding C7 whilst turning on, holding A1a#b1 whilst turning on, all to no avail.
Playing the problem keys softly tends to produce reasonable sound, however, with pressure, the 'tune' is out.
Any suggestions greatly appreciated.
Matt