Jim,
Two, or three, "things" can cause that problem, on that model machine.--
1. Miss-alignment of the TMU, is the most likely, if you have removed it, or the record rack--see the Service Manual.
2. Reversing switch is being "flipped" while the detent switch is closed, and the contact under the TMU is on the A-1 rivet.
3. The TMU has a "burned spot", there beside the A-1 rivet--this is the result of the detent switch being incorrectly adjusted-
("burn" must be"dug-out", and filled with non-conductive material)
Ron Rich