@recordable2000 just looked through a couple of Yamaha schematics and it looks like they use consistently a 2SB1416 PNP transistor. Your S8050 is a NPN transistor. Of course, the SB1416 is obsolete. Here is the datasheet for the [document|40424].
I use [https://alltransistors.com/crsearch.php?mat=Ge&struct=PNP&pc=0.1&ucb=30&ueb=12&ic=0.05&tj=70&ft=0.35&hfe=50&caps=TO1&cf=on|this site] to find equivalent transistors.
A wrong transistor could easily be the cause of your keyboard's issue.