While the Beogram 4002 that I currently restored has safely returned to its owner I still owed a report on the final tonearm adjustments. Beolover blogs all tasks that are performed during a restoration! So here it is as promised:
An important adjustment on the tonearm assembly is the arm lowering limit. This limit prevents the needle from hitting the platter ribs in case the photosensor in the sensor arm fails. The electronic control circuitry has no way to detect this issue and prevent the arm from lowering. If the sensor fails the system will interpret it as 'record present' and lower the arm. This is the main reason why B&O came up with the lower platter rib areas, which are located at the touch down points for LPs and singles. This allows giving the arm a lowering limit that can be below the surface of the record, while still prevent the stylus from being shaved off by a rib should it ever touch down without a record present.
I made a short video about this important adjustment:
After I did this adjustment, I also adjusted the zero weight of the arm (see here for a video how to do this) and installed a nut and a washer to replace the original retaining washer that keeps the counterweight adjustment screw in the assembly. Unfortunately this washer results in a lot of play in the mechanism, which can result in a change of the zero force adjustment during shipping and set-up, i.e. is not acceptable for a Beolover restoration! Here are a couple of pictures showing the original setup,
and the modified one:
All good now in the back of the tonearm assembly!
Beolover, help!
ReplyDeleteI am trying to revive a 4004. I replaced the electrolytics and got it spinning. The problem is that when I start up the turntable the arm travels well beyond the start groove of the record and the arm lowers as it is still moving horizontally. The arm ends up lowering about 3cm in.
Any ideas?