Another Beogram 4002 DC motor was prepped for restoration.

The process began by removing the bearings for an oil infusion.

The small brass bearings were submerged in motor oil, and a vacuum was applied.

Bubbling indicated that the oil was being drawn into the bearings. These bearings took longer than usual, approximately 48 hours, for the bubbling to cease.

After the bubbling stopped, the bearings were taken out of the oil

and the motor was reassembled for testing.

The motor was then installed in a Beogram 4002, and the Beolover RPM device was used to assess performance.

The Beolover RPM device records the RPM over time, allowing for the detection of inconsistencies. The initial measurement (blue curve) was taken with a 0.47uF capacitor (C10) in the motor control circuit. The fluctuations in the blue curve pointed to issues in the motor control feedback. Increasing the capacitance of C10 to 10uF resulted in a steady RPM, as seen in the smooth curve. Notably, this issue doesn’t occur in all motors. The varying performance might clarify why B&O used both 0.47uF and 10uF capacitors in their production. It’s possible that B&O’s engineers were also puzzled by this inconsistency during the 1970s.