Yamaha Full-Size Keyboard "mk tech" Questions

...MK-939S KEYBOARD with no manual, and I basically know nothing about keyboards. The right hand speaker of the keyboard isn't working at all. I am just wondering if it is possibly a setting or a button ...

...turning on - see if this helps. Sounds like a there is a rubber contact that’s allowed debris to get on the circuit board (MK). You may need a tech to disassemble the keyboard assembly to repair ...