You said the drive doesn't show a fault. Are you sure the fault is not clearing itself before you can get to the display. Try it from the machine room while you can watch the drive display. Also try performing a 998 test on the drive. It is much like the 997 self-tune test. It will test all the current loop feedback/ SCR firing type of stuff. I am curious if you are getting a 98 or 99 fault that clears before you get a look at the drive. Certain encoders were famous for having the B B-not channel backwards even though it was wired as marked. While I don't know why this would have changed itself, verify the encoder resolution set in the drive matches the actual encoder ie 1024/2500/10000.
