Vintage Synth Repair

Hi,

I have a polysix that suffered the battery problem, it has been fixed
and sounds great but after the last time I took it to the tech, I've
noticed that the PW/PWM pot isnt working at all.  I'd take it back to
the tech but I've since moved from the area. I've downloaded the
schematics and thought that I'd take a crack at it myself.. I just
wanted to know if anyone has any tips about this specific problem, any
ideas of what could be wrong or any good starting places?

Thanks,
Ian