Beogram 4002 DC Motor Restoration: Oil Infusion of Bearings and New Spark Snubbers

A DC-motor from a Beogram 4002 recently arrived from Austria for restoration. This shows the motor:

Most of these motors need their dry Oilite bearings re-infused with fresh oil under vacuum. For this to happen the motor needs to be completely disassembled:

Then I submerged the bearings in motor oil and pulled a vacuum:

Immediately vigorous bubbling emerged from the bearings, indicating that air was leaving the pores of the Oilite material to make room for fresh oil. After about 48 hrs the bubbling stopped and I extracted the bearings from the oil:

I reassembled the motor and implanted it into one of my Beogram 4002s for a 24 hrs RPM test with the BeoloverRPM device:

The BeoloverRPM can log the RPM of a Beogram over extended periods of time in 10s intervals. The blue curve in the graph below is what this first measurement yielded:

As you can see there were a few RPM drops during that 24 hrs measurement period. If such drops still occur after infusing the bearings with oil, it usually points to unstable spark snubber devices on the rotor of the motor. I took the motor out and extracted the rotor for spark snubber replacement.

This shows the rotor in its original condition:

The snubbers are the three yellowish devices arranged in a circular pattern around the commutator.

I removed the original snubbers to make room for modern TVS diodes, which work well as replacements. This shows the original 'ring' of snubbers together with the replacements prepared for soldering (the contact tabs of their SMD packages need to be bent outwards that they can be soldered to the rotor terminals

This shows the TVS diodes installed on the rotor.

If you try this at home, please, note that the TVS diodes need to be pressed a bit into the windings of the rotor while soldering them in that they are far enough away from the commutator and the brushes. Otherwise they can interfere with the brushes when the motor runs. I put the motor back together and installed it again in the 4002. Another 24 hrs of RPM logging and the red curve in the graph above was obtained. It seems the spark snubber replacement cured the RPM breakdowns. This motor is ready to play some nice vinyl again!