Doepfer

one of my A-111-1 that I bought used exhibits a defect such that when the position of the PWM control is advanced clockwise beyond halfway, the VCO pitch increases about an octave- instead of the rectangular output appropriately transitioning through the remaining duty cycles down to zero.  I have three other fully functional A-111-1 on the same bus which of course do not behave this way. If because of PCB mounting an improperly connected VR terminal is unlikely, would there be an active component responsible for this error? Thanks!