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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

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

Sunday, December 6, 2020

Beogram 4004 DC Platter Motor Restoration

I recently received a DC platter motor from a Beogram 4004 in California for restoration. This shows the motor as received:

I took the motor apart to extract the bearings:
They are the two small donuts on the back pad upfront. I immersed them in motor oil and pulled a vacuum. Immediately, strong bubbling started:
The bubbling indicates that air is being drawn from the porous bearing material by the vacuum. This makes room for the interdiffusion of oil into the bearing. After about 4 days the bubbling stopped and I extracted the bearing from the oil:
Then I assembled the motor and installed it in one of my Beogram 4002s for testing with the BeoloverRPM device, which allows logging the RPM in 10s intervals for extended periods of time:
After abut 24 hrs I had this curve:
This is as good as it gets with Beogram 4004 platter motors. This motor is ready for duty again!

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