I recently obtained a main PCB and DC platter motor from a Beogram 4002. I began with the motor refurbishment, a process that often requires several days for the bearings to become saturated with oil.

The motor is depicted here:

Disassembly was necessary to access the bearings, visible as two small rings on the black component in the front:

The motor’s interior was noticeably oily, suggesting prior tampering. This was supported by a damaged commutator brush that was bent out of its intended form:

I submerged the bearings in motor oil and applied a vacuum, resulting in immediate and intense bubbling:

This reaction signifies that the vacuum is drawing air out of the bearing pores, allowing the oil to penetrate.

While the bearings were undergoing this process, I shifted my attention to the main PCB. Evidence of previous work on this PCB was apparent due to the presence of two trimmers soldered onto the copper side in the upper right corner:

Here is the component side in its original state:

A detailed view of the sensor arm amplifier (TR3):

All electrolytic capacitors were replaced. I also replaced the RPM relay and trimmers with modern, encapsulated versions. Additionally, I installed a new transistor for TR3, as these tend to drift from their specifications, leading to problems with the record detection mechanism.

A close-up of the refurbished RPM section:

Upon completing the board rebuild, I installed it into one of my Beogram 4002 units. I set the bias of the new TR3 to the required 4V at the collector:

The bias trimmer was then moved to the component side:

Next, I assessed the sensor response. The trace below illustrates the measurement taken with the empty platter rotating beneath the sensor:

Each downward spike represents a black ‘rib’ on the platter passing by. The amplitude, exceeding 5V, indicates a strong signal.

After approximately 72 hours, the bearing bubbling ceased, and they were removed from the oil:

I then straightened the brush to the best of my ability

and cleaned the motor parts using an ultrasonic bath. This step removes any remaining oil from the previous repair attempt, as these motors are susceptible to instability if the commutator or brushes are oily. Finally, I reassembled the motor for an RPM stability test. I used my BeoloverRPM tool, which records the RPM at 10-second intervals over a prolonged duration:

The resulting curve from the measurement is displayed below:

This level of performance represents the optimal outcome for the 4002 DC platter motor. Both the motor and PCB are now fully restored and ready to be put back into service.