I recently acquired two DC motors from Beogram 4002 and 4004 turntables located in Denmark. My typical first step is an oil infusion process to address RPM fluctuations, a common issue.

The 4002 motor arrived in this condition:

Disassembly revealed the following:

The two small, donut-shaped brass bearings, visible on the black pad, were submerged in motor oil under a vacuum. Bubbles appeared immediately, indicating the oil infusion process was working. After 48 hours, bubbling ceased, and the bearings were removed:

The motor was then reassembled for testing, using this tool to press in the top bearing:

Installed in a Beogram 4002 turntable, the motor ran for 24 hours. Its RPM was monitored using my BeoloverRPM device:

The 4004 motor underwent the same procedure. The RPM measurements for both motors are shown below:

The top red curve represents the 4002 motor’s 24-hour RPM performance. With a 0.47uF capacitor (C10) in the motor control circuit, it performed well. The dark blue curve shows the 4004 motor’s performance, exhibiting some upward spikes. A second test of the 4004 motor with a 10uF capacitor (C10) resulted in a much smoother, nearly perfect curve. Replacing the 0.47uF capacitor with a 10uF one is recommended for 4004 motors that didn’t come with a factory-installed 10uF capacitor (some do).

The motors are now ready to be reinstalled in their respective Beograms, poised for another 35 years of service.