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Wednesday, February 21, 2018

Beogram 4000: Restoration of the PCBs and the AC Platter Motor

After rebuilding the arm lowering and tracking systems of the Beogram 4000 that is on my bench right now, it was time to replace the electrolytic capacitors and the RPM control relay and trimmers as well as the AC platter motor. This picture shows the original reservoir and motor capacitor setup together with the AC platter motor:
I removed the caps and the motor,
and assembled the new capacitors into the 3D printed holder that I designed to fit the strap that held the original capacitors in place:
Then I took the motor apart for doing an oil infusion under vacuum. This shows the extracted motor:
and opened up after drilling out the two rivets that hold it together:
This shows the rotor with the spring and washers as they are placed on the shaft:
I put the enclosure parts including the bearings into motor oil and pulled a vacuum:
While I let this sit for 24 hrs I focused on rebuilding the PCBs. This shows the main PCB in its original condition flipped out that I was able to access the components:
I replaced all electrolytic capacitors as well as the RPM switch relay and the RPM trimmers that allow to tune the speed:
This shows the RPM section in detail:
The two blue 25 turn trimmers were installed in a way that their adjustment screws are accessible from the solder side of the board:
This is important that one can adjust the RPM while the board is installed. The next step was to rebuild the small power supply board. This shows the original condition:
The two red dots are the only electrolytic capacitors on this board. When I flipped the board around after taking out the three screws that hold it in place the fuse that is located in the yellow tubing in the back came apart:
This seems to be a frequent issue with these fuses, and I think it is time to add replacing them to the standard Beogram 4000 restoration procedure. I installed a new fuse and secured it with some shrink tubing and then installed the board again:
After the bubbling stopped in the vacuum jar I extracted the motor enclosure parts and put the motor back together. Since the rivets that need to be drilled out to open it up also doubled as M3 nuts to hold the tilt adjustment screws of the motor, I used 3D printed parts that I designed a while back to hold M3 nuts in place for the adjustment screws (which I usually replace with hex head stainless screws since they allow much easier adjustment when the platter is installed and running):
Then I implanted the motor together with the capacitor assembly:
This shows the 3D printed parts on the motor in some more detail:
The motor housing is held together by the other two screws that bolt it to the enclosure.
This shows the two 2200uF caps behind the main motor and reservoir caps:
I usually measure the big capacitors after I remove them. Indeed one of them was completely dead showing just a few pF instead of 2000uF:
It is always a good idea to replace all the electrolytic capacitors at this point in time since frequently they are dried out or leaking. Sometimes they even short circuit, which can cause them to burst...not a beolovely sight. After this measurement, I plugged the deck in and started it up. It showed life signs but there still seems to be an issue in the control system since the arm spontaneously lowered when pressing one of the << or >> keys.
















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