Chris,

Is the second typebar that comes up always the same one? That could be a clue.

Regardless, I would stare at the code bars a while at operating speed and see if one looks sluggish.

If you have the ability to make and read an RY tape, that would be a better test than plain text.

A further test would be to put the machine in a test loop,  type an "F", turn the motor by hand and watch each step. (First note which direction the motor turns under power.)

Tom  N3CRK (Typing with one hand while patting myself on the back with the other for fixing an odd ribbon problem on a 28.)