Beogram 4004: Restoration of DC Motor, Main PCB and RPM Adjustment Panel

I recently received a package from Denmark containing the DC motor, the main PCB and the RPM adjustment panel for restoration. Restoration of these three components of a DC motor Beogram can cure RPM stability issues reliably. So I set out to rebuild the PCB with new 105C electrolytic capacitors of Japanese origin. I also installed new RPM trimmers and a new RPM relay. This shows the board in its original condition:

Here an impression after the restoration:

And a detail shot from the RPM control circuit:

This shows the RPM relay in comparison with the original National relay:

Like all Beolover parts featured on this blog, these replacement relays are available to other enthusiasts. Just send an email or use the contact form on the right.

On to rebuilding the RPM adjustment panel. This shows it in its original condition with the bulb covers on:

With the covers removed:

Bulbs taken out:

And LED boards installed:

This shows the LED boards:

They are drop-in replacements based on red/green LEDs that are run in a ratio to yield an approximation of an incandescent bulb emission spectrum. This two-LED approach ensures that there are red photons to illuminate the red RPM scale hands. If amber LEDs were used, the hands would  appear grey if there is no additional incandescent room light present.

This shows the covers back in place:

The final step was to rebuild the DC motor. This shows the motor:

Extracting the oil-hungry bearings requires to taking it apart completely:

Inserting the bearings into oil and pulling a vacuum resulted in the usual bubbling, indicating that the oil infusion process started:

After about 24 hrs the process stopped and I retrieved the bearings from the oil. After soaking up excess oil on the outside

it was time to put the motor back together and do a 24 hrs RPM stability test with the Beolover RPM device to ensure that this restoration was successful. 

Aside from precisely adjusting the RPM, Beolover RPM also allows logging the RPM performance in 10s intervals for extended periods of time. It is available to other enthusiasts who want piece of mind that their Beograms are on top of their RPM game.

This is the 24 hrs RPM stability curve that I measured for this motor as it was controlled by the restored main PCB and RPM adjustment panel:

The RPM fluctuations are well below the discernible level, i.e. the control system of this Beogram is in good shape again.