If the motor voltage drops, the motor could be shorting internally. Also not uncommon. The cure is different - one has to find a way to clear the short. You can open the circuit to the motor, insert a current meter. If the current goes UP just at the instant the motor stops but before the auto-stop triggers, the short is confirmed.
Also, the motor is running much slower in PLAY mode than in FF or REW. Does the motor quit in FF or REW? Even if there is a short on 1/2 of the motor rotation, at a higher speed it skips past the short too quickly to make the mech stop. The average current is higher of course.
Of course there could be some bad connection or other causing the motor drive voltage to drop out...
The issue is intermittent. Have played for 15 min without a stop and also almost instant start to stop.
It is a dual transport machine and both transports exhibit the same problem.
I will play with it again in the next week or 2 and see if I can observe another facet of behavior before taking any action. A schematic would be best as I could probe the input to the drive circuit and see if it is deterministic.