Yamaha Clavinova CLP 820:No sound on middle C key anf F# key .Same on yhe next 3 octoves

Getting no sound on middle C key and F# . Same on the next 3 octaves.

Corroded key contact board underneath the keys - keys are scanned in sets of 6 - if a copper trace is bad any 6th after that is faulty as well - hence C then F# etc etc

You can try fix the broken section - it does work in certain circumstances or buy replacement from Syntaur