By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Thursday, May 4, 2017
Beogram 4004 (5526): Restoration of DC Motor and RPM Stability Test
After restoring the PCBs and implanting LEDs in the RPM trimmer panel it was time to rebuild the DC motor of the Beogram 4004 (5526) that I am restoring right now.
The first step is to extract the motor:
Then a complete disassembly allows getting to the bearings:
The bearings are the two small donuts up front center. Immersing them into motor oil and pulling a vacuum draws out the air that is in the pores of the oil-depleted Oilite brass bearing material:
Every air bubble that leaves the bearings enables an equal volume of oil to enter and replenish the bearing. After about 12-to-24 hrs the process usually stops and the bubbling ends, indicating that the bearing is full of oil again. Then the motor can be reassembled and a RPM test performed. I usually do this with the BeoloverRPM device that I developed a while ago. It allows logging the RPM every few sec and it transmits the measurement via its serial port to a connected computer where the RPM can be graphed against time. This shows the result of a 24 hrs run of this motor inserted into its Beogram 4004:
This is as stable as these DC motors get. The small fluctuations are a result of the analog control system reacting to temperature fluctuations and other external influences.