A few years ago, my old PSR 1000 had a similar problem: notes kept changing
its pitch inexplicably on a given portion of the keyboard. Accidentally,
air from a floor fan. He hit the keyboard and everything went back to normal.
This is probably due to moisture build up on the conductive pads of the keys.
When removing the fan, the fault returned. With that premise, I opened the keyboard and installed
a fan of the type for computers and the failure did not occur again. That model had space
to accommodate the fan, I don't know on current models. You also need to know some electronics,
or contact the technician,
to find the power input (I think it's 18V DC) and connect a voltage regulator IC,
as 12 V DC is required for the fan. The area where I live always has a high percentage of humidity,
at least 79%. It is worth mentioning that this problem did not occur with the PSR S950.
Cheers