I recently obtained a DC platter motor from a Beogram 4002 located in Norway. The motor required repair. The owner had already performed the ‘oil infusion’ procedure for the Oilite bearings. However, after reassembling and reinstalling the motor into the Beogram, the platter’s speed was excessively high and could not be adjusted.

This image displays the motor, without the pulley, in the condition I received it:

Uncontrollably high speed in a DC platter motor usually indicates a problem with one or both of the RPM feedback pickup coils within the motor, assuming the motor control circuit is functioning correctly. This occurs when the coils become disconnected during the removal or reinsertion of the bottom bearing. Verifying this is straightforward: use an Ohm meter to measure the resistance between the red and white leads on the plug. An infinite resistance reading confirms damage to one or both coils.

This is depicted here:

A resistance between 35 and 45 Ohms signifies proper function. This can differ slightly based on the specific motor generation. To proceed, I disassembled the motor and removed the brush carrier, which also houses the two pickup coils.

This image illustrates that:

A close inspection reveals the small, disconnected wires on both sides. This issue necessitates delicate repair work. The process involves carefully unwinding a section of wire under a microscope until a resistance of roughly 15-25 Ohms is achieved between the coil’s two ends. In this instance, it appears previous repair attempts had been made, as the coil windings were cut to a certain depth. Consequently, I dedicated time to unwinding, tinning the end with solder (essential due to the insulating coating on the “magnet wire”), measuring open circuit resistance, continuing to unwind until reaching the cut portion, and then starting again. Eventually, I located the intact end of the wire and successfully measured the correct resistance.

This photo shows the reconnected coil:

And this image shows the removed wiring:

The second coil underwent a similar repair process. Following the successful restoration of both coils, I reattached them to the brush carrier.

Here is the brush carrier after being reinstalled:

This is the final resistance reading between the red and white wires:

With the motor reassembled, I installed it in a Beogram 4002 for testing. I used my BeoloverRPM device to measure the RPM.

This graph shows the results:

The results are optimal for the Beogram DC platter motor. The motor is once again functional.