By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Monday, April 9, 2018
Beogram 4002 and 4004 DC Motor Restoration
I recently received two DC motors from a Beogram 4002 and a Beogram 4004, both located in Denmark. As usual, I started with the oil infusion process since it solves RPM stability issues in most cases. This shows the 4002 motor as received:
I took it apart:
The brass bearings are the two small donuts on the black pad up front. I immersed them in motor oil and pulled a vacuum:
Immediately, bubbles emerged from both bearings. This indicates that the oil infusion process has started. After about 48 hours the bubbling stopped and I extracted the bearings:
Then I reassembled the motor for testing. This shows the tool I use for pressing in the top bearing:
After assembling the motor I installed it into one of my Beogram 4002s and ran it for 24 hrs recording the RPM with my BeoloverRPM device:
I did the same process for the 4004 motor. This shows the RPM curves that I measured:
The red curve on top shows the 24 hr RPM performance of the 4002 motor. It performed fairly well with a 0.47uF capacitor in place for C10 in the motor control circuit. The dark blue curve shows the same measurement for the 4004 motor. some upward spikes are evident. I ran this motor a second time with a 10uF value in place for C10. This quieted the situation down and a near perfect curve was measured. So I recommend to replace the 0.47uF with a 10uF value if the 4004 did not come with a 10uF value factory installed (some do).
Time to send this motors back to their Beograms. They are ready to serve for another 35 years...;-).