Got my newest purchase, a CT-F2121 up and running with new belts, idlers and sensor switch. Works fine Except I just noticed the Auto-Stop doesn't work on Play back, it'll just sit and hum but, kicks off fine on RR and FF. Any ideas? Had to replace the original sensor switch because it would kick off after a few seconds. Although I used a sensor switch from a CT-F7171 to replace it, and you would think they'd be the same. Book does call for two different part numbers between the two but, I figured being they are virtually the same machine except for a few things that they may have just change the part number. Maybe that's the problem? Any insight would be appreciated greatly.