As promised, heres a quick clip of the problem
https://youtu.be/YOWNPDpr3oY
I did reverse the motor and encoder wiring and as I suspected, the problem direction reversed. That is to say, the problem was still happening when I pressed the CCW button but the turret was spinning in CW direction.
Problem is now definitely isolated to the electrical end and not a overcurrent trip due to mechanical binding.
Options:
1- bypass the current sense transformer on the turret amp card
2- replace all capacitors on amp card
3- replace output transistors on amp card
Anyone have any better ideas?
I really don't want to go and buy a $2500 replacement amplifier card and have it not solve the problem.