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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, June 30, 2020

Beogram 4002 DC Platter Motor Restoration

A Beogram 4002 DC platter motor recently arrived from Washington State for a restoration. This shows the motor as received:
After a quick bench test for life signs, which yielded the typical rough running noise caused by dry bearings, I took the motor apart to get to the bearings:
the bearings are the two small donuts on the black pad up front. I immersed them in motor oil and pulled a vacuum:
Immediately, vigorous bubbling started from the bearings, indicating that air was drawn from the porous Oilite brass bearing material into the vacuum. This air extraction makes room for oil inter diffusion into the material. This is how Oilite bearings provide lubricant to the shaft. But over time the oil gets depleted, and then it is time to replenish it. After about 72 hours the bubbling stopped, which means that the pores are filled again. I extracted the bearings:
and reassembled the motor to give it a RPM stability test in one of my 4002s with the BeoloverRPM device, which allows logging the RPM in 10s intervals over extended periods of time. Ideal for detection of sporadic RPM variations:
This is the curve I measured over about 24 hrs:
This is as good as it gets with the Beogram 4002 DC motors. Time to send this motor back to Washington State!

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