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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...

Tuesday, October 9, 2018

Beogram 4002: DC Motor Restoration

A Beogram 4002 DC motor from London in need of restoration recently arrived. Most Beogram 4002/4004 DC motors are in need of getting their Oilite brass bearings re-infused with fresh oil at this point in time. The oil stored in these porous brass bearings is drawn out over the years, resulting in dry bearings that are the main cause of RPM variations in Beograms. This shows the motor as received:
Extraction of the bearings requires disassembly of the motor:
The two small donuts on the black pad are the bearings. I put them in motor oil and pulled a vacuum:
The air bubbles emerging from the bearings indicate the air drawn from the bearings due to the vacuum. This makes room for oil diffusion into the bearings. After about 48 hours the bubbling stopped and I extracted the bearings from the oil:
Then I re-assembled the motor and installed it in one of my Beogram 4002s for a 24 hrs RPM stability test with my BeoloverRPM device,
which allows logging of the RPM over extended periods of time. A great tool to check the health of a platter motor, since RPM fluctuations usually are inconsistent over time, and it is difficult to pinpoint issues by listening to records alone.
This is the RPM graph that I obtained after about 24 hrs:
This is as good as it gets...this motor is back in business and will soon travel back to its Beogram in London!

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