Beogram 4002 DC Platter Motor: Replacement of Spark Snubbers

A Beogram 4002 (5513) DC platter motor that I restored in 2016 returned to my bench due to noticeable RPM variations. In 2016 I had re-infused the bearings of this motor with motor oil, but did not replace the spark snubbers. At the time, the motor performed well after the infusion process.

I first installed the returned motor in one of my 4002s and took a 24 hr RPM stability measurement. What I measured is the blue curve in this graph:

The erratic spikes in this curve suggested one or more malfunctioning spark snubbers. 

I opened the motor up and extracted the rotor. This shows the commutator end of the rotor with the original spark snubbers (blue devices):

I removed the snubbers. This shows the original ones with their replacements (modern bidirectional TVS devices):

I soldered the TVS units between the rotor poles:

Then I re-assembled the motor and ran another 24 hrs RPM test. This test yielded the red curve in the above graph, which is similar to the curve I measured in 2016. This motor is back in business!