Beogram 4002 (5513): Restoration of DC Platter Motor Bearings with Oil Infusion Under Vacuum

While I am having the Beogram 4002 (5513) that lost its solenoid plunger on my bench, I decided to redo the DC motor. When I initially restored this deck I did not know yet that one needs to infuse the brass sleeve bearings with oil under vacuum if the fix is supposed to have lasting effect. Just putting some grease on the bearings quiets them down temporarily and stabilizes the RPM performance, but after a few weeks usually the effect of the grease wears off and RPM variations start occurring again.

Here are a few impressions of the process. The motor needs to be completely disassembled to get the bearings out (and more importantly, back in):

The next step is to infuse the bearings with oil under vacuum. I use a mason jar and a FoodSaver vacuum pump for that. As soon as the vacuum is established air bubbles arise from the bearings:

This is a result of the expansion of the air in the pores in the brass due to the low pressure in the jar. The escaping air makes room for the oil that can then diffuse into the bearing.

A typical Oilite bearing contains about 20% oil by weight. This is enough to provide an oil field on the bearing surface for many hours of motor operation.

Once the bubbles stop (typically takes about 12-24 hrs) the bearing is full of oil again and there motor can be reassembled. This shows the brushes carrier plate with the bottom bearing reinserted:

The top bearing is held in place with a ring whose tabs need to be forced back flat to hold the bearing in place securely. I designed a special tool for this task that allows me to use adjustable pliers to press the tabs down:

The red cylinder goes inside the motor housing and the orange part is used to press the tabs down against the red part. This results in a bearing that sits snugly in its cradle below the top shaft orifice:

Once the bearings are back in, the motor can be put together and the PCB soldered back on:

At this point the motor needs to be tested with a bench supply. It is imperative that the brushes carrier plate is installed in a way that the rotor rotation is not impeded. This can be reliably quantified by observing the current that the motor draws while spinning freely at 5V. In my experience the lowest current that can be achieved is below 30mA. If there is too much friction the current will be higher. If that is the case the bottom plate needs to be loosened and carefully retightened while turning the screws in small steps in sequence until they are tight. It can take a few attempts until the lowest current can be achieved.  This shows my bench supply with the motor running after I was done with this process.

Once the current is right, the motor can be inserted into the outer noise canceling shell and then reinstalled in the Beogram.

It is a good idea to test the motor for a few hours to make sure that everything is stable and up to specifications. I did that with my BeoloverRPM device that allows to measure the RPM over time and log it via the serial port of a computer. This is the graph that I measured for this motor over about 8 hrs:

This looks as it should! This Beogram 4002 is ready to be shipped back! Hopefully this time it will stay away a bit longer!