Hope I can get some help from the group.
I am debugging a Drive ][ I have where the spindle appears to the running at about half speed.
I haver verified that
the belt is not slipping
the spindle (big flywheel) spins freely withe belt removed
the motor spins freely when not powered
Adjusting VR1 (to both end points) changes the speed, but never lets me the speed correct (not even close)
So starting thinking electrical, looking at pin 7 of the speed control chip the voltage was reading kind of low like 10.5 volts vs 11.8 and the motor seemed to not have alot of torque.
I had a spare speed control chip and swapped that out but with no change in performance.
So I am about to start really digging and tracing through the whole speed control board, but thought I would ask if anybody had any advice first.