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Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Tuesday, October 11, 2016

Beogram 8000: Repair of a Scraping Sub-Platter with a 3D Printed Insert for the Main Bearing

The next item to look into with the Beogram 8000 that I am restoring right now was that the sub-platter scraped along on the chassis. This shows the interior of the 8000 with the sub platter still in place:
Somehow the platter was situated a few 1/10ths of a mm lower than usual, which made it touch the sub-chassis base plate in a few spots. This prevented the deck from maintaining a constant speed (it never showed 33.33 on the display, just 33, which is a signal that the RPM is off). Also it made an intolerable mechanical noise. Far from Beolovely! 
This seemed strange to me (there is no way to adjust platter height like one could in a Beogram 4002) and so I poked around a bit on the internet. I came across an uttering by one of the greats in this business, Dillen of Beoworld: "Typical symptom of a broken main bearing nylon insert. It happens often if the Beogram was transported with the heavy platter mounted or just put down too hard." (my customer confirmed that the ebay seller did not take out the main platter when he/she shipped it to him...).
He went on to say "The whole weight of the platter, hub and sub-platter rests on the very sharp pointy tip of the hub spindle. Only fix is to replace the nylon insert."

This shows the spindle after lifting out the sub-platter:
In the pic the tacho sensor is already out of the way (it swings away by moving the brass lever clockwise). In that position one can pull out the spindle:
The picture shows the pointy end of the spindle that rests on the plastic disc that Dillen mentions in his post.
The plastic disc can be pushed up using a small hex wrench or similar (there is a small hole on the bottom of the bearing that can be accessed from underneath the enclosure. This shows the white plastic (probably nylon) insert in the main bearing:
And after pushing it up:
First I tried to simply flipping it around, but there is no indentation on the back of the plastic part for holding the spindle in the center of the bearing. So my idea was to simply shimming the insert up a bit to lift the platter back to its normal height. The insert still seemed in decent condition, only the indentation was a tad too deep after the incident, causing the platter to be too low. 

I designed a small disk that I printed with my 3D printer:
After a few tryouts with different thicknesses it turned out that 0.7 mm was a perfect thickness to raise the platter just enough to not scrape anymore (test with the main platter and a record on top if you do that at home...).
The disc is easy to insert when the insert is up sideways:
Once the printed disc was next to the insert, it is straight forward to push the parts back to horizontal and down into the bearing.

Once I installed the spindle and the platter again, everything was fine. No more scraping, and the platter turned freely.

1 comment:

  1. This is all good advice and will permanently solve that problem. The proper clearance for the bottom of the sub-platter is 0.5mm. If you raise it higher than that, problem will be in getting the platter height low enough without bottoming out the suspension at the rear right leaf spring. There is very room to give away there and it isn't easy to see that it has happened. I make the shim out of 24-20 ga. aluminum, installed exactly as shown here. Keep that clearance to 0.5mm max.


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