This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...
Thursday, March 10, 2016
Beogram 4000: Adjusting the Platter, Floating Chassis, Arm Lowering Limits and Tracking Weight
Now it was time to adjust the platter, the sub-chassis and the arm lowering limits and tracking weight. Check my Beogram 4000 page for some posts and videos about this procedure. But first I needed to replace the cabinet guiding washers that were either replaced with simple washers or had cracks:
There is a video about this procedure in my Beogram 4002 playlist. The guidance washers can be ordered directly from my Shapeways store. This is the direct link to the part.
These washers are very important for proper seating of the aluminum plates, which in turn is essential for being able to properly adjust the sub-chassis and platter height. This shows one of the washers installed:
They are a faithful reproduction of the excenter washers used in later models.
Then I adjusted the platter and the chassis to achieve a concentric location of the platter in the cutout of the main aluminum plate:
After the chassis and the platter are adjusted the arm lowering limit can be set. There is 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 400x 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.
After this the tracking force can be calibrated. There is also a video about the tracking force calibration process.
And then it was time to give this Beogram 4000 a test drive! Oh, wait...not yet! It occurred to me that I hadn't adjusted the Wien oscillator that drives the AC motor. It needs to oscillate at a certain amplitude. This is done by connecting the oscilloscope between the coupling and phase capacitors of the motor and ground. After adjusting the 33 RPM voltage I got these nice curves. This one is for 33 RPM where 6.5V RMS need to be adjusted.
And the depending (there is nothing to adjust) curve for 45 RPM:
Another interesting aspect of this issue is the almost fully transparent vinyl, which makes this a great test record for the disc detection mechanism of the Beogram!