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Wednesday, February 14, 2018

Beogram 4000: Restoration of Arm Lowering and Tracking Systems

I started working on the Beogram 4000 from Germany. As usual, I restored the arm lowering and tracking mechanisms first. This shows the arm lowering solenoid and damper assembly:
I took the linkages and the solenoid out for cleaning and lubricating:
Once everything was back together clean and well-lubricated, it was time to take the sensor arm out to get to the damper-to-arm linkage, which is often stuck due to hardened lubricants. This shows the back of the arms:
Taking out the two screws at the bottom of the sensor arm assembly released the arm:
After removing of the locking washer the linkage can be taken out:
I cleaned the pivot bearing and put a bit of synthetic grease on the pin and then put everything back together. The next step was to align the arms that they are parallel to each other and orthogonal to the carriage rods:
The next step was to replace the cracked carriage pulley. This shows the original plastic pulley
and this the machined aluminum replacement:
Beolovely! Send me an email or use the contact form on the right if you are interested in getting such a pulley for your own Beogram. I'll be happy to get you in touch with Nick who provides them to the B&O community.
Finally, it was time to replace the original incandescent light bulb in the tracking sensor with a Beolover LED assembly. This guarantees long term stability. The bulbs often break and they are not available anymore. This shows the original setup:
The bulb is in the square black housing in the center of the photo. Taking it out reveals the tracking sensor aperture:
This shows the original bulb assembly in comparison to the LED replacement:
The LED sits in a spot close to the location of the filament of the light bulb. The blue trimmer that is integrated with the LED assembly allows the adjustment of the LED intensity, which is very practical when adjusting the tracking sensor feedback sensitivity. This shows the sensor implanted:
The LED light source is available to other B&O enthusiasts. Just send an email or use the contact form if you are interested.
The final act of this part of the restoration was to replace the old grimy sheet metal screw that clamps the aperture assembly to the tonearm assembly. This shows the original screw:
These are notoriously difficult to tighten and it is a great idea to replace them with a modern hex driven M2-12 mm bolt and a M2 nut, which can be tightened easily without changing the aperture alignment while doing so. On to rebuilding the electronics.

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