Beogram 4002: DC Platter Motor Restoration

I recently received the DC platter motor of a Beogram 4002 from a customer in Ohio. The deck showed the usual RPM variations indicative of dry motor bearings.

This shows the motor as received:

I disassembled the motor to extract the bearings:

The bearings are the two small donuts on the black pad. I immersed them in synthetic oil and pulled a vacuum. Immediately bubbling started around the bearings:

The bubbles represent air being drawn from the porous Oilite material. As the air leaves the bearings fresh oil can diffuse into the evacuated pores. The process took about 2 days until the bubbling stopped.

I reassembled the motor and then it was time for a 24 hrs RPM stability measurement with the BeoloverRPM device. It is able to log the RPM every 10 seconds into a serial port of a computer. This shows the BeoloverRPM in action:

This is the data I collected over 24 hrs:

There is still a degree of slow long-term RPM variations. These should go away after playing a number of records, which will polish the bearing surface in its new position. This motor is ready for duty again!

Beogram 4004 DC Platter Motor Restoration Using Dksoundparts Bearings

I recently received the DC platter motor of a Beogram 4004 from a customer in the Netherlands. This customer wanted me to install new reproduction bearings he had purchased at the dksoundparts store.

Normally, I re-infuse the original bearings with oil under vacuum. So it was an interesting experiment for me to see if there is a difference in outcome. 

This shows the motor as received:

I took it apart as usual:

The original bearings are on the black pad up front.

The new dksoundparts bearings came in a small metal can:

I took them out of the can. They are oily since they were also infused with oil under vacuum:

This shows them installed in the top and bottom parts of the enclosure:

If you try this at home, make sure the larger bearing goes into the top part and the smaller into the bottom.

After closing the motor up it was time for a 24 hrs RPM stability test with the BeoloverRPM device:

In its 'slow' mode the BeoloverRPM sends an RPM measurement every 10 sec to a computer serial port.

This is the curve I measured after about 24 hrs:

This curve looks a bit 'wilder' than the curves that I get for most of my restorations using the original bearings (see for example this restoration project for a comparison). This does not really come as a surprise to me since over time I came to realize that it is important to re-install the original bearings in the same orientation as they were installed originally. This significantly shortens the time it takes to break in the bearing. It seems the bearing surface gets polished around the main contact area defined by the pull of the platter belt, which over time lessens the amount of RPM fluctuations. 

When installing new bearings there is no already polished area, so they always need to get broken in. I expect this motor will probably clam down after playing it for a few hundred hours. I suspect that new Beograms back in the 1970s had this issue, too, but no one noticed it since these variations are well below the threshold humans can detect.

I thought it would be interesting also measuring wow and flutter (short term RPM variations introduced (mainly) by the feedback loop that keeps the RPM constant in DC motor Beograms).

This can be done in 'fast' mode with the BeoloverRPM.

This is the curve I measured during about 60 platter rotations:

In fast mode the BeoloverRPM logs a RPM measurement every time a platter rib passes under the sensor. In other words one gets 24 measurements per rotation. The above graph looks 'complicated' since the actual RPM variation measurement is superimposed by a measurement artifact caused by minute variations in spacing between the platter ribs around the platter. Since the time between ribs passing is measured and then converted into an RPM value, changes in the spacing results in proportional changes of the calculated RPM. This causes the observed zig-zag pattern (the 'platter pattern'), which is added to the actual RPM variation. The true RPM variation in turn corresponds to the slower wave pattern that is superimposed onto the platter pattern. An evaluation of the graph seen here suggests an RPM variation of maybe 0.2%. 

When using the original bearings I usually get something around 0.1%, i.e. a slightly better performance. This probably also has to do with the rougher surface inside the new bearing that challenges the feedback loop a bit more causing more variation.

It would be very interesting to measure this motor again in a couple years after this Beogram played a few hundred records. I would expect to see a better performance.

After this experience, I think one can say that it may be better to use the original bearings if possible. But the new bearings available at the dksoundparts store are a viable alternative if a vacuum setup is not at hand. It would be interesting to know how the results with new bearings compare statistically, i.e. after doing a larger number of motors with them. What I know from my restorations with re-infused original bearings is that in a small number of cases (<5%) the restoration results can be less than satisfactory.

In general, this discussion is pretty academic since even 0.2% variations are much smaller than the 0.7% threshold where humans begin noticing pitch variations.

In summary it can be concluded that this motor is ready for duty again! Time to send it back to the Netherlands!

 

Beogram 4004: Restoration of the DC Platter Motor

I recently received the DC platter motor of a Beogram 4004 from a customer in Minnesota for an oil infusion of its bearings.  

This shows the motor as received:

I disassemble it to get the bearings out:

The bearings are the two small donuts on the black pad upfront. I immersed them in synthetic oil and pulled a vacuum. Immediately bubbling started:

The bubbling represents air being drawn from the porous Oilite bearing material. As the air leaves the material oil can diffuse into it. This process can take up to three days. After the bubbling stopped I extracted the bearings from the vacuum chamber:

Then I re-assembled the motor and installed it in my bench Beogram 4002 for a 24 hrs RPM stability test with my BeoloverRPM device:

In its 'slow' mode the BeoloverRPM is able to log the RPM in 10s intervals into a serial port on any PC. This is the curve I had measured after about 24 hrs:

This graph is about as good as it gets with Beogram DC platter motors after restoration. In my experience the slight choppiness will go away over time as the top bearing settles in. This motor is ready for another tour of duty!

Beogram 4004: DC Platter Motor Restoration

I recently received the DC platter motor of a Beogram 4004 from a customer in Poland for restoration. It exhibited the usual RPM variations due to dry motor bearings.

This shows the motor as extracted from the packaging:

I disassembled the motor to extract the bearings:

The bearings are the two small donuts on the black pad. I immersed them in oil and pulled a vacuum:

Immediately strong bubbling started. This is indicative of air being drawn from the empty pores of the Oilite bearing material. This makes room for oil to diffuse into the bearing, replenishing its oil reservoirs.

After about three days the bubbling stopped and I extracted the bearings from the oil:

I reassembled the motor and installed it in one of my Beogram 4002s for a 24 hrs RPM stability test with the BeoloverRPM device:

The BeoloverRPM allows logging the RPM in 10s intervals for extended periods of time, perfect for detecting sporadic RPM fluctuations. Luckily with this motor no significant fluctuations were detected. This is the curve I measured:

A very nice curve! This motor is back in business and can be sent home to its Beogram!

Beogram 4002: DC Platter Motor Restoration

I recently received the DC platter motor of a Beogram 4002 from a customer in Utah for restoration. Most Beogram 400x platter motors have dry bearings these days, and that usually results in intermittent RPM variations that get increasingly worse. Re-infusion of the bearings with oil is the cure for this issue.

This shows the motor as received:

I took it apart to get to the bearings:

The bearings are the two small donuts on the black pad upfront. I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

This bubbling is indicative of air being drawn from the empty pores of the Oilite bearing material. Once the air leaves, the remaining vacuum allows oil to diffuse into the material. The process usually takes about 2-3 days until the bubbling stops. Then it is time to extract the bearings:

I re-assembled the motor and then it was time to give it a 24 hrs RPM stability test with the BeoloverRPM device:

The BeoloverRPM allows logging the RPM for extended periods of time in 10s intervals, perfect for spotting intermittent RPM inconsistencies. This is the curve I measured after about 24 hrs:

In terms of short term variations this curve is as good as it gets with the Beogram DC platte motors. The long-term drift is a sign for bearing and shaft 'getting used to each other' in their new orientations after the infusion process. The RPM will stabilize in a few 10s of hours. Until then it is a good idea to check the RPM periodically to make sure the speed is close to spec.

Beogram 4002/4004: Restoration of Two DC Platter Motors

I recently received two DC platter motors from a Beogram 4002 and a 4004 for restoration. As in most cases these two motors had dry bearings causing RPM variations.

This shows the two motors as received:

A look at the bottom plates of the sound proofing enclosures revealed the manufacturing dates:

The 1976 motor is from a Beogram 4002, while the 1979 dated motor is from a 4004. They are almost identical in construction, except that the younger motor has a white plastic brush carrier in comparison to the brown FR-2 PCB material of the earlier design. This shows the 1976 motor taken apart to get the bearings out. They are on the small black pad upfront:

After immersing the bearings in motor oil and pulling a vacuum strong bubbling occurred as the air was drawn from the porous Oilite bearing material:

I did the same for the 1979 motor. After about three days the bubbling stopped for both of the bearing sets, indicating completion of the oil re-infusion process. I extracted the bearings from the oil

and re-assembled the motors. Then I installed each of them in one of my Beogram 4002s and tested them with the BeoloverRPM device, which can log the RPM in 10s intervals for extended periods of time:

This graph shows the two RPM curves that I measured over about 24 hrs for each motors:

The red curve corresponds to the 1979 4004 motor, while the blue curve (shifted for clarity) was measured for the 1976 4002 motor. Both curves are pretty similar and show the usual, probably temperature related, long term drift and some minor wiggles as the shafts polish the reoriented bearings. 

These motors are ready for business again!

Beogram 4002: DC Platter Motor Restoration

I recently received a Beogram 4002 DC platter motor from a customer in New York City. It exhibited the usual RPM instabilities that come from dry bearings.

This shows the motor as received:

I took it apart to get to the bearings. They are the two small donuts on the black pad upfront:

I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

Bubbling indicates that the vacuum draws the air from the empty pores of the Oilite bearing material. This makes room for oil to diffuse into the material. After about 3 days the bubbling stopped. This meant the pores were full with oil again. I extracted the bearings:

I reassembled the motor and installed it in one of my Beograms. Then it was time for a RPM stability test with the BeoloverRPM device:

It allows logging the RPM over extended periods of time. This is the curve I measured after about 24 hrs:

This is a decent curve, but there are still some minor variations (they are much smaller than what one can discern while listening to music). I see this once in a while with restored motors. My hypothesis is that the top bearing and the shaft are at a slightly different position relative to each other after the refurbishment, and so the shaft needs to 'polish' the bearing a bit before the motor will run more stable again. In my experience this may take a few days or even weeks of running time.

At any rate, this motor is ready for duty again and will soon be shipped back to be reunited with its Beogram 4002!

Beogram 4004: DC Platter Motor Restoration

I recently received the DC platter motor of a Beogram 4004 from Germany for restoration. The deck exhibited the usual RPM fluctuations suggestive of dry motor bearings. This shows the motor as received:

I took it apart to extract the bearings for oil infusion. They are the two small donuts on the black pad up front:

I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

The bubbling means that the vacuum pulls out the air from the porous Oilite bearing material, and that makes room for oil to diffuse into the material. After about three days the bubbling stopped, and I extracted the bearings:

I put the motor back together with the rejuvenated bearings and installed it in one of my Beograms for testing with the BeoloverRPM device:

The BeoloverRPM allows logging the RPM for longer periods of time. This is the curve I measured after about 24 hrs:

It looks pretty good! This motor is ready for duty again!