troubleshot stepper motor failure

my original prusa i3 mk2's left z axis stepper motor started skipping steps. this is how i determined that it was the left z axis stepper motor and not anything else. since i had a second printer, i could easily swap motors between printers. when i did this, the problem followed the motor, so now my second printer started failing..

[@kaidos2754]

check the wires there might be broken
and give false signals to the motors depending on the state of connection

[@Nigmye]

i had a similar problem with a stepper getting stuck. all i did was loosen the screws holding it together and then tightening them again. i noticed that the tighter i'd make them, the smoother it would rotate.

[@ozzloy]

oh? i'll give that a shot. the motors started sticking again after this. i did try taking the motor apart and putting it back together again. i'll try tightening the housing more. i never did fix this. too low priority for me to get around to it. thanks for the comment!

[@MarinusMakesStuff]

I think it might be a broken bearing in the motor, did you try to open it up? I'm curious what was the problem.

[@ozzloy]

i ended up taking apart the housing and found no loose parts. after putting it back together, the motor worked for a few prints. then locked up again. prusa was kind enough to send a replacement.
i think the housing was just slightly misaligned. the rotor was catching the stator. the bearing worked smoothly.