I have a new NEMA17 2-phase 4-wire off a 3d printer that doesn't go. I switched it to another verified-good axis drive and it didn't run, this is the motor for sure.

Here's the thing:
The motor can turn CW smoothly, and strong. But it doesn't go CCW at all, just weakly vibrates.

This is weird. See, if you lose a winding on a motor, then it can't turn. The working coil just cycles from +/- to -/+ and back, CW and CCW look the same to the working coil. It will shake but cannot turn in either direction.

I checked for cross-connection shorts that might have connected the B-winding to the A. I could imagine that could interact with the drive's logic and cause something unusual. But there isn't anything. Both winding impedances look good.

Anybody know of a motor-specific (not drive) failure that could cause a motor to only turn one way??