Vintage Synth Repair

hi folks, im  wondering if anyone has any ideas on this issue:

i have a cs-40m that has 2 pot functions not working-but i know its
not the actual pots. (checked on a DVM).
 
so something else is obviously down that would cause these pots to
function as if they were FULLY open, even though, by my diagnosis, i
am getting the voltage changes i should be at the output pins of the
pots, as well as their respective output pins of the board it is
on.(VCO 1 voltage=VCO 2 voltage, at WAVESHAPER OUTPUT pins.) i have
not been able to figure this out via schematic-what i THOUGHT  was the
multiplexer responsible for encoding is apparently NOT the problem.
 
so, if you have the ability to look at a schematic, and be able to
tell which parts/chips could be responsible for these two pots
functions,that would be hugely fantastic.(i have been told that
multiplexer 4000-series chips are a good guess, but after swapping
several chips i thought could be the culprits, i have yet to find the
culprit). i will upload the schematics in the files section now. 

 
thanks much for the help-rj