Vintage Synth Repair

> 
> Any recommendations? 

Actually, the first thing I'd do is thoroughly clean the connectors
between the various boards and the key busses.  Sitting in a closet
for years, they are sure to have oxidized.

It's a zero dollar first step and might do it.

If you have CV out jacks on the back, check to see if there is any
voltage (and voltage change) from them when you play the keyboard.

Good luck.