[R-390] Adjusting Linearity Stack Collins PTO

[Jim M.]

I am looking for instructions for adjusting the linearity stack in a
Collins PTO.  I have the PTO in an external jog now with a frequency
counter and a calibrated scale and have the end points pretty close, but
there is still 1-2 khz error midpoint.   I suspect the stack needs
adjusting.  It seems to be connected to a large screw that is accessible
from the rear of the PTO (after opening it.  Any info out there?