Beogram 4002 (5523): Rebuilding the Arm Lowering Mechanism, and Tracking Sensor Bulb Replacement and Adjustment

The first thing to do with a Beogram 4002 is usually a rebuild of the arm lowering mechanism and an adjustment of the tracking system. In this case the mechanical setup suffered from hardened lubricants and the tracking sensor sensitivity was much too high causing a runaway carriage after lowering the arm. Here is a picture of the solenoid and damper assembly:

The first step was to take it apart and clean and re-lubricate everything:

There is a video that shows the tracking sensor adjustment procedure in detail. After putting everything back together, I took the sensor arm out to get to the damper-to-arm linkage:

This video shows how to get to the damper to arm linkage and re-lubricate it. After putting things back together the tonearm aligned again with the sensor arm by means of the notch in the plate on the back of the counter weight assembly:

If everything is done properly, the arms should be fully parallel after this procedure and perpendicular to the back of the enclosure:

The next step was to fix the tracking system. I usually recommend to install a LED based light source into the system to ensure long term stability. This shows the original tracking sensor light source:

And here is the SMD LED based replacement unit that I recently designed:

The original incandescent unit is also shown for comparison. Like all my parts this assembly is available to other enthusiasts.

After putting in the new light source, I adjusted the tracking system feedback loop sensitivity. After a coarse mechanical adjustment using the excenter behind the light source, I fine tuned the sensitivity using the blue trimmer potentiometer that is integrated in the LED light source:

There is a video that shows the tracking sensor adjustment procedure in detail. It is a good idea to do this adjustment with an unwanted LP (some free jazz by Sam Rivers is a great choice for this task) and not your best cartridge. It is possible that the carriage drags the stylus across the record if one is not careful while doing the adjustment. After these procedures the tonearm and the carriage behaved normally again. On to a rebuild of the electronics.