Hello,
Did you manage to repair the unit already?
A hobby of mine is repairing the somewhat older Yamaha PSR series keyboards. I have already repaired several of them, even glued the keys and of course cleaned them.
You don't want to know how much dust there can be in it after 30 years....
I also repaired a PSR 6700 today.
The Rhythm section buttons, and the + - buttons of the tempo control didn't work anymore.
After a thorough cleaning of all the contact points both the pcb's and the rubber buttons, I got it back together in one piece. Fantastic instrument. especially the interactive acompaniment with solo style is very nice....
Next project is a PSR 740, there will be a Gotek bay in it, and I want to see if the brightness of the double LCD screen can be adjusted, because it is actually too bright ... is therefore difficult to read.....
We wil see...