By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Thursday, October 20, 2016
Beogram 4002 (5501): Final Touches - AC Motor Calibration, Adjusting Platter and Sub-Chassis and Tracking Force
The restoration of the Beogram 4002 (5501) that I am currently working on is coming to an end. I gave the aluminum panels and the platter a deep clean, and then did the sub-chassis and platter height adjustments followed by an adjustment of the tonearm lowering limit and the tracking weight.
There are two videos on my YouTube channel that show how to adjust the platter bearing and the subchassis (in a Beogram 4000, but the process is very similar in the 4002). There is also a video on my youTube channel that shows how to adjust the lowering limits. This is a very important procedure since the control system of the 4002 cannot guard against photosensor failure in the sensor arm. If the sensor fails the arm will be lowered whether there is a record or not, possibly endangering a very expensive cartridge. The correct adjustment of the arm lowering limit can prevent stylus failure if that happens. And finally, there is also a video about the tracking force calibration process.
After all that was done, I adjusted the AC motor waveforms. This is done by connecting an oscilloscope to the connection point between the motor capacitors and ground:
Then the oscillator trimmer is adjusted until clean waveforms of maximum amplitude are achieved. The end result looked like this for 33 RPM:
and for 45 RPM:
Then I adjusted the RPM precisely with my BeoloverRPM device. Personally, I still use the original design. The updated design is available to other enthusiasts. The BeoloverRPM is very convenient for the occasional RPM adjustment (yes, the belts do become elongated over time causing the RPM to slowly drop). Here are two pictures showing my adjustments for this Beogram with its new belt:
Very nice! And then it was time to set the unit up next to my Beogram 6000 4-Channel:
I celebrated this restoration with a record that I just bought: Gabor Szabo's "The Sorcerer":
This record is rapidly becoming one of my all time favorites. An amazing live concert recording that has a remarkably raw power that sucks you into Szabo's rhythm.