After rebuilding the electronics of the Beogram 4002 (5513) that I am working on right now it was time to restore the DC motor. They all need their brass sleeve bearings infused with oil under vacuum. This requires to disassemble the motor. This shows the motor as extracted from the Beogram:
I took it apart:
The bearings are the two small donuts on the black pad. I immersed them into motor oil and pulled a vacuum. Immediately vigorous bubbling started as the air was drawn from the porous Oilite bearing material:
These bearings took more than 48 hours until the bubbling stopped, which signified that the oil content in them bearing material was replenished. I extracted the bearings from the oil
and reassembled the motor. then it was time for a 24 hrs RPM stability test with the BeoloverRPM device, which allows logging the RPM every 10 sec for extended periods of time. This is a great tool for pinpointing intermittent RPM fluctuations, which is very difficult to do otherwise. BeoloverRPM is available to other enthusiasts...just send an email or use the contact form on the right. This shows the BeoloverRPM in action:
After about 24 hrs I was able to make this graph with the logged data:
This is as good as it gets for the DC motor Beograms. The gradual change over time is probably temperature related...a bit of influence by the moon phase may also be part of the equation (just kidding...;-). The joys of analog control systems!
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