Beogram 6000: Oil Infusion of AC Platter Motor Shaft Bearings

I recently received the AC platter motor of a Beogram 6000 (Type 550x) from a customer in the Netherlands. The motor exhibited knocking noises that could not be adjusted away by reducing the motor voltage. This is usually a sign of dry motor bearings. My remedy for this issue is reinfusing the Oilite motor bearings with synthetic oil under vacuum.

This shows the motor as received:

After a trip to my garage for drilling out the rivets that hold the enclosure together, I disassembled the motor:

It is important to keep the parts on the shaft in their original order and orientation (the washers have an orientation, too!):

Unlike the later DC platter motors, there does not seem to be a straightforward method for removing the shaft bearings from the enclosure halves of the AC motors. Therefore, I simply put the entire enclosure into the oil. This is a bit messy, but it works well. This shows the initial bubbling coming from one of the submerged bearings while the pump labored to pull a vacuum:

A few minutes after the lowest pressure had been reached, the oil had foamed up:

These bearings were pretty thirsty! But I think some of the bubbling up air also comes from pores in the enclosure itself. The infusion process is completed when the bubbling stops. At that point, all the pores are again filled with oil. After two days, the oil became quiet, and I removed the parts from the vacuum chamber. This shows one of the bearings after I cleaned out the oil:

These bearings look pretty similar to the ones found in the later DC motors. They can also adjust their angle to minimize misalignment with the shaft.

I put the motor back together:

If you try this at home, make sure the stacked coils are re-inserted at the correct polarity (purple and green wires need to be on the same side as before, otherwise the motor will run backwards). Since opening these motors requires destroying the threaded rivets that hold the enclosure together, I developed 3D printed plastic parts (red) with integrated M3 nuts for the tilt adjustment screws. Note that without the rivets, the enclosure is mostly held together by the mounting screws after the motor is bolted back into its place in the Beogram. This is not an issue for the operation of the motor, but it needs to be kept in mind when the motor is reinstalled.

Beogram 4000 AC Platter Motor Restoration

I recently received the AC platter motor of a Beogram 4000 in Massachusetts. The motor exhibited 'knocking' noises, which could not be alleviated by adjusting the motor voltage or tilt. My usual 'answer' to this issue is taking the motor apart and immersing the enclosure halves in motor oil and pulling a vacuum to fill the pores of the material with oil. This shows the motor as received:

I drilled out the threaded rivets and took it apart:

Then came the oil infusion step:

After a couple days the bubbling stopped and I reassembled the motor. Since the rivets cannot be re-used I provide 3D printed brackets that hold the motor together when it is bolted back into the Beogram:

This motor is ready for duty again! 

Beogram 4002 AC Motor Restoration

I recently received an AC platter motor from a Beogram 4002 for restoration. This shows the motor as received:

I removed the pulley, drilled out the rivets and opened it up to extract the rotor and the coil carriers:

Then I submerged the housing halves in motor oil and pulled a vacuum:

Vigorous bubbling started as air was drawn from the assembly.

After 24 hrs the bubbling stopped and I cleaned the parts from excess oil and reassembled the motor. Since the removed threaded rivets cannot be used anymore, I provide 3D printed nut carriers that allow adjusting the motor tilt with two new screws, similar to the original threaded rivets:

If the motor is not associated with a particular Beogram 4002, I always supply additional nut carriers and M3 screws in case the motor is used in a Beogram with belt guides, which also need threaded rivets. See here for an example for a motor with belt guides (usually to be found in earlier Beogram 4000s).

Beogram 4000: Restoration and Adjustment of AC Platter Motor

After rebuilding the electronics of the Beogram 4000 that I am restoring right now it was time to look into the AC platter motor. This particular Beogram 4000 has the old style pulley that does not have belt guards integrated, i.e. they added guards on the posts that hold the motor:

These guards are not really needed since the pulley is slightly crested which securely holds the belt on the pulley. The vertical position of the belt can be adjusted via the tilt of the motor.

Similar to the DC motors of the later Beogram 4002 and 4004, the AC motors also develop dry bearings. This motor made this clear via a noticeable 'knocking' noise when driving the platter that could not be adjusted away via the motor voltage trimmer or motor tilt (without platter some 'cogging' can be normal, since the motor is 'bored' without platter, hence the phase lag for smooth operation between rotor position and AC voltage is too small) . So I took the motor out

and disassembled it:

Disassembly requires drilling out the rivets that hold this motor together:

The standoffs (left most parts in the above picture) need to be reused once the motor is reassembled, i.e drilling should be done carefully in small steps to limit damage to the parts. Since they also served as rivets, they needed to be drilled out with a 3 mm bit to allow 25 mm M3 screws all the way through. 

Anyway, the bearings cannot be extracted without doing damage, so I usually put the entire motor housing in the oil and under vacuum:

After 24 hrs I reassembled the motor using 3D printed 'nut arresters' that allow the replacement of the rivets with M3 bolts and nuts:

the purpose of these parts is to hold the nuts in place under the motor that the tilt screws can be adjusted when the motor is installed. This is how the parts fit on the motor:

After re-installing and adjusting the vertical position and tilt of the motor, I adjusted the motor voltage. Per manual this is to be done at 33 RPM that the sine wave measured at the connection point between motor coupling and phase capacitors is maximized without showing distortion:

This motor could be adjusted to 6.5V RMS as specified in the manual. At 45 RPM is still had 6.0V:

There is no way to adjust 45 separately, i.e. one has to live with whatever 45 shows when 33 is properly adjusted. But 6.0V is plenty to drive the platter vigorously. This motor seems to be back in business!

Beogram 4000: Restoration of AC Motor

A while ago I realized that the AC motor of the Beogram 4000 that I restored started making distinct knocking noises in sync with the pulley rotation when I played it. This was a sign that the Oilite brass bearing needed an oil re-infusion. Oilite bearings are porous brass bearings that get factory oil infused under vacuum. Over time the oil is dispensed onto the shaft of the motor and from there into the motor housing. This means that after a certain run time the bearings need to be replaced or re-infused. If you have a food vacuum sealer, this can be done with a mason jar. Here are a few impressions of my process:

First the motor needs to be removed

Then the two rivets that hold it together need to be pressed or drilled out:

This shows the motor opened up:

and a peek at the bearing in the bottom part:

For the record, this shows the arrangement of a spring and washers on the motor shaft:

Since after removal of the coils there is only metal left, one can simply put the entire enclosure into oil and pull a vacuum:

The usual air bubbles formed as the air escaped the brass pores. After about 24 hrs the process came to a halt, indicating that the bearings were again full of oil.

Since the rivets had to be destroyed for opening the motor, I replaced them with two 3D printed parts that hold M3 nuts enabling to put the pitch adjustment screws back in:

This shows the motor back in the enclosure:

After this procedure the motor was quiet again.

Beogram 4002 (5501): Repair of 'Knocking' AC Motor

I usually like to take my time for testing Beograms that I restored to make sure there are no intermittent issues. Sometimes also additional problems arise when one starts using them again on a routine day-to-day schedule. And so it happened with the AC motor Beogram 4002 (5501) that I completed recently. After playing a number of records I noticed a faint 'knocking' coming from under the hood. After removal of the aluminum plates I realized that the knocking was in sync with the rotation of the AC motor. First I tried to adjust the motor tilt, which brought some reduction of the noise, but after a while it always came back, and it also grew in intensity the more records I played until it was clearly audible whenever a quieter track was playing. Absolutely unacceptable for a turntable!

There was only one option: Take the motor apart and have a look! This shows the motor installed (with my 3D printed capacitor adapter in the background):

I removed it from the enclosure. Unfortunately, the AC motor is soldered in, i.e. one has to unsolder the leads to take it out:

This motor is held together by two rivets with M3 threads that also serve to hold the leveling screws. Sometimes these rivets have already failed at this age of the Beogram and it is easy to extract them, but not in this case. I had to remove them with force. One of the came out by applying a bit of pressure with adjustable pliers:

With the other one I was not that lucky and I had to drill it out on my work bench. After that was accomplished the motor opened up:

This shows the rotor and the parts that are on the shaft:

this shows one of the Oilite brass bearings:

They look very similar to the bearings that are in the later DC motors.

Unfortunately, one cannot easily extract them. Or at least I did not see an obvious way, and in the absence of a spare motor to replace this one, I elected to leave them in place of the oil infusion process. This meant I had to put in the entire motor housing into my mason jar and put it under vacuum:

The usual bubbles formed after the vacuum was pulled. After 24 hours I took the parts out and drained the oil onto an absorbent paper towel for another 8 hours. then I wiped everything dry of oil. This process worked fairly well. I put the motor back together. In absence of replacement rivets I designed 3D printed parts outfitted with M3 nuts to hold the adjustment screws. This shows the part on the side facing away fro the enclosure:

and on the enclosure side (there is less space, i.e. it had to be a bit more spartan):

This shows the motor installed with these parts:

When the motor is bolted in like this it is held together securely by the two mounting screws that are in the two other orifices in the motor housing.

Testing of the motor after this procedure demonstrated that the knocking was gone and that the RPM was stable. I guess the lesson learned here is that the 4002/4000 AC motors also needs restoration at this point in time to re-infuse the dried out bearings with oil. But it seems the issue may be a bit rarer than in the DC motors, where almost all of them seem to be afflicted by dry bearings. I am hypothesizing that this difference may be related to the lower RPM of AC motors, which should consequently result in less oil being removed from the bearings per number of played records. 

Beogram 4000: Adjusting the Chassis Springs and the Platter Height

The Beogram 4000 that I am rebuilding right now is entering the 'beautification phase'. It works now very well, and what is left are the exterior and a new good plated plug etc...So I set out to adjust the platter height and tilt and the leaf springs that hold the floating chassis of the turntable. This task is a relatively complex one since one has to "try[] to hit a bullet with a smaller bullet whilst wearing a blindfold, riding a horse" (to say it with Scotty in the 2009 Star Trek reboot...;-). Since sensor arm orientation relative to the floating chassis, platter tilt angle relative to the chassis, linear travel in the opened transport lock and belt tension all play significant roles in the adjustment process, one needs some patience and may have to redo things a few times until one hits the sweet spot where the platter is centered and leveled with the aluminum panels and parallel to the arms, and the chassis does not touch the locks when they are open.

I recently made a couple of videos that show the basic approach. They are posted here. Here are a few pictures of the fully adjusted platter relative to the aluminum panels:

And an 'in-action' detail. She is getting real pretty now!..;-): 

The aluminum panels were quite dirty on this unit. Here is an area in comparison before and after cleaning with Mr. Clean Magic Eraser pads and some (hand-) dishwashing detergent:

Before:

And after:

What would we do without Mr. Clean??!!

Beogram 4000: Exchanging the Electrolytic Capacitors, the RPM Relay, and Adjusting the Motor Signal

I marched on with the restoration of the Beogram 4000 that is on my bench right now. After replacing the reservoir and motor capacitors, I went ahead and replaced all electrolytic caps on the main and power supply board with Japanese made 105C grade long lasting units. I also exchanged the RPM relay, since I recently extracted several dead or inconsistent relays of this type from Beogram 4000 and 4002 units. This made me think that these relays should be part of any 'full' restoration to ensure long-term stability. My goal is to get these elegant vintage beauties to a new-like performance and reliability. These pictures show the main PCB in its original state. This is the solder side. There is one Tantalum capacitor in the top left corner that was added post-PCB-design. Even the Danish masters go through a learning curve, I guess...;-):

Here is the component side:

And a detail shot of the RPM relay:

This is a picture of the relay component that I recently developed. It uses a modern encapsulated SMD relay that is broken out with a small PCB that fits precisely to the pinout of the original relay. Hence it can be plugged straight into the original solder pads and no external wiring is necessary. Plug'n Play!

This assembly is available to other enthusiasts. Just send me an email if you are interested.

This shows the PCB after replacing the capacitors and the relay:

This shows the replaced sole cap on the solder side:

On to the power supply board. It has only two Tantalum caps on it (the red dots):

And here with new ones:

After replacing the boards and testing that everything was working properly, I adjusted the motor signal. The AC motor is run by an on-board Wien bridge oscillator whose feedback needs to be adjusted for the right oscillation frequency for 33 and 45 RPM. There is also a potentiometer that controls the amplitude that goes into the power amplifier that finally drives the motor. I recently made  some more detailed posts (link 1, link 2) about the adjustment procedure. Here is a picture that shows how to apply the probes for the measurement:

One needs to be careful to select the right end of the phase capacitor to get the correct amplitude as prescribed in the manual for 33 RPM (6V). Here are the oscilloscope shots after I adjusted the trimmers to spec. This is the 33 RPM trace

and here is the one for 45 (it will usually be a bit lower than 6V and there is no way to independently adjust it - this is analog technology!..;-):

Beautifully clean traces in this unit! Absolutely lovely! This is Beolove!