The majority of Beogram 4002 turntables equipped with a DC motor require motor refurbishment. Indicators of this need include abrupt drops in revolutions per minute (RPM) or audible motor noise during operation. This specific Beogram 4002 (5514) exhibited significant noise during unloaded operation. As part of my restoration process for all 4002 turntables, I comprehensively rebuild the DC motors to preemptively address these common issues.

The primary contributor to these performance issues lies in the brass sleeve bearings. These bearings, designed for “permanent” lubrication, feature a porous brass construction infused with oil under vacuum. While initially effective, this lubrication method has a finite lifespan, eventually leading to oil depletion and performance degradation.

The scarcity of comparable low-voltage DC motors with suitable inductive tacho control feedback in the current market necessitates a different approach – replenishing the bearings with oil to extend the motor’s operational life. This procedure entails complete motor disassembly to ensure proper bearing extraction and reinsertion. The following image displays the disassembled motor, with the bearings highlighted in the “front row”:

Upon removing the bearings, I submerged them in a mason jar and applied a vacuum using a FoodSaver pump. The emergence of air bubbles from the bearings provided immediate confirmation that the oil infusion process was underway:

After a 24-hour period, the process concluded, with no further bubble formation observed:

Research suggests that these bearings typically contain approximately 20% oil by weight.

Following the infusion process, I retrieved the bearings and proceeded with reinstallation. The image below illustrates the bottom bearing installed within the brush carrier:

The top bearing installation necessitates securing the holding ring onto the spring that maintains the bearing’s position. Here’s the bearing with its corresponding spring:

After slightly manipulating the holding ring’s tabs:

I employed my specialized tool in conjunction with adjustable pliers to fully clamp down the tabs:

This action guarantees a secure fit for the bearing, replicating its pre-disassembly state.

Subsequently, I reassembled the motor:

After soldering the PCB back in place, I proceeded to test the motor using my bench supply:

A correctly assembled motor should exhibit a current draw below 30mA at 5V. Higher current readings suggest the need to loosen the brush carrier plate and subsequently retighten the screws in small, incremental steps, working sequentially around the motor (similar to tightening a vacuum flange).

These motors demonstrate sensitivity to proper shaft alignment with the bearings, directly impacting their performance. Another prevalent issue arises from incorrect motor rotation direction after assembly (or a complete failure to run). This typically stems from improper angular mounting of the brush carrier plate relative to the motor’s permanent magnets. Addressing this involves removing the screws, rotating the bottom plate by 120 degrees, and attempting operation. If the issue persists, an additional 120-degree rotation should rectify the direction. Marking the alignment with a Sharpie pen before disassembly can greatly simplify this process.

In this instance, the motor appears to be functioning correctly once again, with the previous grinding/screeching noise eliminated. I will conduct an RPM test using my BeoloverRPM device after rebuilding the main PCB and replacing the RPM relay and trimmers. These components represent additional common culprits behind unstable RPM performance in Beogram 4002 turntables equipped with DC motors.