I’m posting this in case others have encountered what I’m going to describe (and know the cause).
Press Play, arm moves to record, drops and plays all the way to the end, lifts and begins to return but becomes stuck. When I looked at the mechanism, I found that the arm pulley (1634) and cam gear (1636) had become misaligned and were binding. After repositioning these, the arm worked normally for a while. But then the issue recurred. Has anyone else experienced this in the 5900 series? Short of a worn part or a strong shock/hit to the turntable, I can’t see what would cause these to become misaligned again on their own.