@discnik, most likely cause are one of two things.
1. the tape is not tracking correctly in reverse direction.
2. There is a large switch assembly in the bottom of the deck mounted to the large PCB. If these contacts get dirty over time, when you reverse play the deck the contacts will not make a good connection, giving you no signal or a garbled signal.
Try cleaning these contacts in the reversing switch and see if it helps.
1. the tape is not tracking correctly in reverse direction.
2. There is a large switch assembly in the bottom of the deck mounted to the large PCB. If these contacts get dirty over time, when you reverse play the deck the contacts will not make a good connection, giving you no signal or a garbled signal.
Try cleaning these contacts in the reversing switch and see if it helps.