My vintage Technics SL-BD20 turntable has worked perfectly for a very long time. In fact, since the late 1980s this turntable has been absolutely fantastic!
Unfortunately, some weeks ago the tonearm suddenly stopped performing an automatic return at the end of a record. This was a big mystery and I was totally clueless as to what could have been the nature of the problem.
The SL-BD20 is a belt-drive turntable. The motor has a shaft that drives a belt which in turn spins the platter. Within that drive train is an additional mechanism that causes the tonearm to return to the “rest position” when it reached the end of a record. The key to the system is the platter spindle. That spindle turns with the platter. As the spindle turns the press-on gear, which you can see in the photos, causes a larger gear to turn and the tonearm mechanism to operate.
After a rather long time analyzing the situation I finally discovered a very small crack in the nylon gear that is pressed onto the platter’s spindle. The press-to-fit attachment method causes some degree of stress in the nylon. After many years the stress caused a fracture.
In the photos on the right you can see the spindle. In the lower photos you can see a closeup of the crack in the gear.
The easy solution was to simply buy a replacement spindle. A separate gear is not necessarily available, and there is a chance that attaching such a gear to the original spindle would cause it to fail in the same way the original did.
With the spindle and gear assembly replaced the Technics turntable is back to working like new.
