I have a Tascam 122MKIII which had a bad idler tire. I replaced it, but now I'm having a problem. When I attempt to play a tape it plays for a few seconds then stops. It also does this in FFW and REW, each moves for a second or two then stops. The tape isn't bound up, but free and easy to move. Is there a tape motion sensor I may be dealing with? Any help would be appreciated.