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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Monday, October 11, 2021

Beogram 4002 551x: Exciting!! Replica DC Motor Bearing Prototypes from Beoparts Successfully Tested

I had received a second set of Beogram 4002 platter motor/main PCB and RPM panel for restoration from a customer in the Netherlands. As usual I started with the motor:

I took it apart to extract the bearings.
Usually, I would have now shown a picture of the bearings infusing with oil under vacuum. But this motor restoration is special! I recently received a set of custom made new Oilite bearings for these DC motors from www.beoparts-shop.com for testing. This shows the original bearings (top) in comparison with the new ones:
Exciting!! I installed them and reassembled the motor. 
The next step was to rebuild the main PCB. I replaced all electrolytic capacitors, the RPM relay, RPM trimmers and I installed a new high-gain transistor for TR3. This shows the board after restoration:
Then I replaced the incandescent bulbs with LED assemblies in the RPM panel:
And then it was time for testing everything in one of my Beogram 4002s. The first step was to adjust the TR3 bias properly with the 5M precision trimmer that I install as a replacement for the fixed value R26. First it needs to be installed on the solder side, so one can adjust the collector voltage to 4V while everything is plugged together:
Then it can be moved to the component side:
The next step was to measure the sensor response. This shows the oscilloscope trace I measured:
Each dip corresponds to a black platter rib passing by.
Once proper sensor operation was established I finally got to test the performance of the new bearings with a 24 hrs RPM stability test using the BeoloverRPM device:
And this is the curve I measured:
I would say this is an excellent result, as good as it gets with Beogram DC platter motors. This demonstrates that the new beoparts replacement bearings work as well as re-infused original bearings. A great simplification of the restoration process!

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