My first keyboard was a PSR 2100.
Just like your 2000, mine had the same issue.
It was suffering from old age and a great deal of use.
After trying many things to fix it, I sadly had to say good-bye to my first Yamaha.
I found out that the solution was far too expensive, more than the price I paid to buy it.
In other words........you should consider replacing it with a more recent board.
Sorry to break it to you.
Regards,
Ron