Beogram 4002 DC Motor Restoration

A repair shop in California recently sent me a DC platter motor of a Beogram 4002 for restoration. This shows the motor as received:

I took it apart to extract the bearings which always need oil infusion under vacuum since after almost 40 years they are usually running dry. This shows the disassembled motor:

The two small donuts on the black pad are the bearings. I immersed them in motor oil and pulled a vacuum. Immediately vigorous bubbling started:

This indicates that air is drawn from the pores in the Oilite bearing material making room for oil to diffuse inside. After about 48 hours this process stopped and no more bubbles were visible. I reassembled the motor and put it into one of my Beogram 4002s for a 24 hrs RPM stability test:

This photo shows the BeoloverRPM device which can log the RPM of a Beogram for extended periods of time. This device is available to other enthusiasts. Just send an email or use the contact form on the right if you are interested.

This shows the RPM curve that I graphed after about 24 hrs:

This is as good as it gets for the 4002 DC motor. This motor is ready for duty again. I should mention that this curve was measured with a 10uF value in place for C10 on the main board. This capacitor determines the sensitivity of the feedback based RPM control loop. For some reason a fraction of these motors need a 10uF cap in place, while others benefit from 0.47uF or 0.33uF. This motor tested poorly with a 0.33uF value (which, I was told is also installed on the main board of this Beogram), but yielded the above nice curve with the 10uF value. The joys of analog control systems!...;-)