[Al Skierkiewicz]

Tom,
I have ask ...Are you using CAN? What you describe (50% FWD/REV) is an electronic technique for holding a motor stationary. Effectively it is a brake unlike the short that "brake mode" puts across the motor. According to my documentation this mode is only available in the Jaguar with the CAN bus implementation. (New and improved Jaguars may have this built in, I don't have the latest docs for new Jags) It is capable of being generated externally under software control but you would know if you had programmed it in your software. As you describe it, this mode would emit a high frequency squeal from the motor. Are you using feedback from the arm for position?

I agree that two motors having shorted windings is rare but it does happen. Although the window motor has the worm drive, moving an arm is likely to rotate the motor just a little. That is all it would take to get you to cross a segment boundary. I have not disassembled one of these motors in a while so I can't remember how many poles the motor has. Have you measured the free speed? With a shorted winding, it should be vastly lower than the stated free speed, 89 RPM I think.