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 4002 (5513): DC Platter Motor Not Spinning Anymore

I restored the PCBs, DC platter motor and RPM panel of a Beogram 4002 from a customer in California in January 2021. Recently he contacted me stating that the platter motor stopped spinning. I asked him to return the parts so I could have a look.

After I received them I implanted them in my bench 4002. Indeed the platter motor did not spin anymore! The culprit was found quickly after checking the motor voltage at the red wire of the motor harness. I only measured 2.4V. It should be around 9V if everything is o.k.

The motor voltage is stabilized by 1TR2, originally a TIP31 power transistor. Since the Zener diode still made ~10V, it was most likely the transistor. I replaced it with a stronger TIP41:

And everything was good again in the motor voltage department. 9.6V at the red lead!:

In 2021 I had not understood yet that the power transistors on these boards often have issues. Maybe age related, maybe just wear from years of playing records. Informed by repeat transistor failures that I encountered over the years, I now always replace them all when I restore a Beogram 400x. So I set out to update this board to my current state-of-the-art. It is best to replace the two power transistors mounted on the solder side of the board when the board is installed. It makes it easier to position them correctly that the mounting holes match up. This shows 1IC1, which regulates the 21V power rail. It is usually a TIP120:

I always try replacing power transistors with stronger types for enhanced longevity. In this case a TIP102 is a good choice:

For some reason modern TIP replacements need some capacitance at their emitter in this circuit configuration to prevent high frequency oscillations superimposed to their emitter output. That is why I soldered a 100nF cap (yellow-orange) between the emitter and a conveniently located GND solder point nearby in the above picture.

The second transistor on the solder side, 1IC4, is usually a TIP125, 

whose stronger cousin, the TIP107, makes a good replacement:

After this I removed the board and also replaced the often fail prone H-bridge transistors with new types. this shows the updated board with the extracted parts:

I installed the board again and successfully tested all functions. These parts are ready for duty again and will soon travel back home to their Beogram 4002 in California!

Another Surprise Addition To The Workshop Beogram 4004

 Back in 2021 I restored my own personal Beogram 4004 turntable, dubbed the "Workshop Beogram 4004".  That same year I added the Beolover Remote Commander to it and have happily been playing a lot of records with it.

This year I have another surprise addition to my Beogram 4004...a Beolover SyncDrive Platter Motor.

Ever since reading the Beolover Blog announcing the Sync Drive I have been wanting to try it out.

As I mentioned, my Beogram 4004 was already restored and I use it regularly.
The DC platter motor had been restored by Beolover back in 2021 and works great.

However, I love the idea of a self calibrating platter motor that is even more accurate and was ready to try it out in person.

First, I remeasured the original DC platter motor using the Belovover RPM Tool v2.
I wanted to have current values to compare the original platter motor with the SyncDrive.

This screenshot shows the measurements from the Beolover RPM Tool v2 being recorded on a PC.

I ran the measurements for twenty hours.  Of course that is way longer than a platter motor would ever be run in normal use but it has been the length of time we usually collect RPM measurements on the Beolover Blog for comparison.

After saving off the measurement data for the original platter motor (at 33.33 RPM) I switched out the motor with the new Belover SyncDrive.

The changing of the motor is incredibly easy.

Here is the Beolover SyncDrive as received from Beolover.

Here is the connection point to the Beogram 4004 main board.

Here is the SyncDrive installed.

...and turned on by starting the platter turning and pressing one of the SyncDrive control buttons.

The SyncDrive came on showing me that my current settings have a 33.33 RPM value that is a little too fast.  Not surprising since I hadn't run a calibration with the SyncDrive yet.

Here is the Beogram 4004 platter speed measurement with the SyncDrive installed and after it calibrated itself for 33.33 RPM.

How great is that?  So easy.

My favorite features of the SyncDrive are its control buttons.
I love being able to run automatic, self calibration for 33.33 and 45 RPM.

I also really like locking out the original Beogram control panel speed adjustment controls.

Now for the measurement comparison.
Using the Beolover RPM Tool v2, I also measured the 33.33 RPM of the Beogram 4004 platter using SyncDrive.  Again, I ran the measurement for twenty hours.

Looking at the measurement results you can see that both platter motors produce a consistent and controlled platter speed for twenty straight hours.

That is what I expected.  After all, my original DC platter motor was restored by Beolover back in 2021 and should easily last another forty years.

However, you can also see how much tighter the RPM measurement is with the SyncDrive controlling the speed.

Also note that the mean for the original platter motor shows that it had drifted a bit slower than my original setting in 2021.  It measured a mean value of 33.24 RPM.  
The 33 RPM trimmer on the Beogram 4004 main board could be used to readjust that along with a good measurement tool like the Beolover RPM Tool v2.

With the SyncDrive motor that type of readjustment is no longer necessary.  You simply press the Auto Cal. button and two minutes later the platter speed is calibrated and locked in.

With either a Beolover restored DC platter motor or a Beolover SyncDrive, a Beogram 4002/4004 owner can get a beautifully functioning turntable.  I just prefer (and appreciate) the technical achievement and performance of the SyncDrive.

Now back to listening to records.

Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suffer from dry motor bearings and/or bad spark snubbers. This often causes very noticeable RPM variations that ruin the listening experience. These motors can be restored by oil-infusing under vacuum, but even when restored, they do not measure up to the original AC platter motors or the later linear drives in the Beogram 8000 and 8002. Often there is significant RPM drift due to temperature variations and other environmental influences, and the analog feedback-based RPM control circuit causes fairly strong wow and flutter compared to the AC-motor Types and the 8000 series.

Once I realized the relative inferiority of the DC drive a few years ago (and also being slightly annoyed by restoring one DC platter motor after another..;-), I started working on an adequate replacement for these motors. I desired an upgrade for DC Type Beograms that would make them as good as the other models. This took me on a long and pretty interesting journey exploring different motor types and control approaches.

I finally settled on a brushless three-phase motor. The motor in the final design is custom manufactured for best performance and it is synchronously driven. The control system is able to measure the actual RPM of the platter, which enabled an auto-calibration feature that allows precise RPM adjustment.

I made a (rather long...sorry!...;-) video that explains the in and outs of the SyncDrive, demonstrates installation, use and gives a discussion of its performance relative to the other Beograms of the day. Enjoy:

The SyncDrive is available via the Beolover Store. Send an email to beolover@gmail.com if you are interested/have questions.

If you rather read than watch: Here is a short summary of the most important aspects:

The SyncDrive is an easy plug-and-play installation without the need for soldering (see video below). This is how the SyncDrive looks installed in lieu of the original motor:

The board bolts directly to the mounting posts of the original DC motor, and the electrical connections are made by a single wire harness that connects to the main board:

This picture indicates the essential features of the SyncDrive:

The speed sensor measures the platter speed from below, using the platter ribs in the same way the BeoloverRPM device uses them from above.

The user interface is activated by pressing any of the four buttons while the platter rotates. Once pressed, the indicator LEDs come alive and the interface is ready to interact. The buttons allow automatic calibration of the RPM and manual adjustment (33 and 45 are independently adjusted/calibrated depending on the actually selected RPM of the Beogram). Furthermore, the influence of the RPM panel above the keypad can be deactivated if desired. This can be useful if there are issues with the potentiometers in this panel, or if accidental RPM change is to be prevented.

I characterized the performance of the SyncDrive using the BeoloverRPM device, which allows precise RPM measurements and log them over time. 

This shows a direct wow and flutter comparison between a restored DC-motor and the SyncDrive:

The measurement covers about 60 turns of the platter. The 'noise' in these spectra is caused by small variations of the spacing between the platter ribs. Since the BeoloverRPM device measures the time between the passing of ribs under its sensor, slight variations of the spacing introduce a measurement artifact. The two shown measurements were performed in the same Beogram with the same platter, i.e. have the exact same platter pattern. This allows a direct comparison. The red curve was measured with the SyncDrive installed, while the blue curve was measured with a restored original DC motor. The 'beating' pattern of the blue curve is an indication of the analog control system acting to keep the RPM constant. In essence, the RPM of the original motor 'meanders' around the 33.33 set point in an attempt to stay close. All feedback based control systems operate that way: The actual RPM is compared with the setpoint, and when the RPM is too low, the motor speeds up until it is measured too high, then the process reverses. This causes a wavy trajectory of the actual RPM around the set RPM. The art of feedback systems is basically to keep such variations at a minimum. The analog control system of the 4002 does a pretty decent job, but it is no match for the precision of synchronous motors, which do not rely on feedback, but rather on a very stable oscillator that determines the RPM top-down, and the motor simply 'obeys'. Precise oscillations can be generated with high accuracy, which makes such motors superior as platter motors.

This can be clearly seen when comparing the performance of the earlier AC platter motors found in Beogram 4002 550x Types and the original 4000. This graph shows the above two curves in comparison with a curve measured on a restored Beogram 4000, as well as the later 8000 and 8002 types:

The pink curve was measured on the 4000. It is clear that the performance is much better than the DC motor, which is a direct result of the synchronous operation of the can stack AC motor of the 4000, which is driven by an analog Wien precision oscillator. The slight waviness of the curve is most likely the result of the elastic coupling between the motor pulley and the platter causing a weak 'jo-jo effect'.

It is interesting to compare the performance of the belt drives with the later linear motors of the Beogram 8000 and 8002. Sonavor kindly contributed the green curves when I sent him the redesigned BeoloverRPM for testing. The overall RPM stability seems very similar to the 4000 and the SyncDrive. This is interesting since the linear drive in the 800x is a feedback based system. Here we see that feedback does not need to be bad if it is well designed. The linear drive benefits from the absence of a belt, which takes the elastic coupling out of the equation. A digital control system coupled with high-resolution feedback from an ~80 slots tacho disk seems to be sufficient for a fairly precise control that is much better than what was achieved with the analog control of DC motors. It is interesting to compare the two green curves: The much smoother 'platter pattern' of the 8002 is a result of its different platter design: The earlier 8000 still used a 4002 style platter, and consequently its platter pattern is similar to the measurements on the 400x. The (likely) etched platter of the 8002 seems to have more smoothly varying spacings between the platter ribs. I do not know how they really made these platters, but the smooth variations suggest a projection aberration during pattern generation for the etching process.

It is satisfying to see that the SyncDrive is matching up fairly well with the early 4000 and the later 800x.

When it comes to long-term stability the SyncDrive is actually better than the early 4000:

While the 4000 has a much better wow and flutter than the DC motor 4002, it has similarly strong longterm RPM drift. This is not a surprise, since its Wien oscillator is analog, and therefore also more easily affected by temperature variations. The SyncDrive compares favorably with a much smaller drift, courtesy of its digital control system. Unfortunately, we were not able to perform such measurements on Beogram 8000 and 8002s (yet!...;-). They shut down after 30 min if they recognize that no record is being played. I suspect that their RPM stability is also pretty good due to their digital control system.

In summary, I think the SyncDrive turned out to be a nice upgrade for any DC-motor Beogram, bringing them to AC-motor Beogram level (and likely even 8000 and 8002 level in terms of RPM stability).

Beogram 4000: Platter Motor Stopped Working

Last year I restored a Beogram 4000 from a customer in the UK. Unfortunately, he recently contact me since the platter motor stopped working. 

After receiving the unit I put it on the bench and started looking into the issue. first I checked the power rails and the reed relays. Everything tested fine. The next step was verifying the motor signal. I measured at the motor capacitor, and there indeed was no signal.

So I did the classic 'follow the signal' approach. I measured the oscillator signal at the collector of TR8, which checked out o.k.: 

The oscillation is not a perfect sine wave, since I had to replace the light bulb in the Wien oscillator with diodes when I restored it last year.  But so far so good...now I measured at the base of TR9, which should essentially show the same signal, just shifted to zero V since it is coupled via C6 to loose the DC component. But the signal was gone:

So it had to vanish somewhere between TR8 and TR9. I measured all the connections between TR8 and TR9, and it turned out that the signal vanished after the motor trimmer VR3. I replaced VR3 with a modern 5k 25 turn trimmer, but no cigar! The signal was still gone after the trimmer. At that point it dawned on me that there must be a short to GND somewhere. A closer inspection of the board yielded this:

R24 and R20 were touching! Something had bent the two resistors together, which effectively connected the base of TR9 to GND. I bent the resistors apart, and voila: The motor signal returned. This is the 33 RPM trace

and here is the 45 RPM.

So the trimmer had been replaced unnecessarily. This shows the new unit peeking through the access hole in the PCB for adjusting the motor voltage:

I put the platter on and a cartridge to see if I could play a record successfully. But the arm did not lower on the record. I realized that the sensor arm was dark, i.e. no power to the LED light source I had installed last year. I measured the voltage at the LED and it turned out that it was 0V. So I looked for interruptions in the connections between the PCB and the LED. And quickly I found the culprit: The yellow wire that connects 6V to the carriage had broken off its terminal on the PCB:

I soldered it back on, and now the deck is playing beautifully again! I will play a few more records, and then it should be time to travel back to the UK.

Beogram 8000: An Exploration of the Platter Speed Sensor (Includes Oscilloscope Traces for the Most Important Signals)

I recently received a Beogram 8000 as a parts unit for repairing another Beogram 8000. I wanted to exchange the circuit boards in the hope to alleviate a strange issue that I sadly was not able to figure out. So I rebuilt the boards of the donor 8000 and then plugged them into the other unit.

And then my fun exploration of the platter speed sensor began...;-). Here is what happened: I plugged the Beogram in, and pressed Play. Immediately the platter ramped up madly to about 100 RPM and the "33.33" never appeared (it shows that a stable speed has been reached by the system). The display stayed at "33". 

Head scratching etc...ensued. The first thing I did was plug the board into the other Beogram to see if its platter would also go out of control. It did not. So what gave?

Well, it turned out that some of the Beogram 8000 with old style boards (i.e. with the two piggybacked small boards on the upper end of the main board) did already come with the speed sensor used in the later Beogram 8002. This are the two circuit snippets in comparison:

First the older version:

Note R46 and R47. They are on the main board in this circuit. Now look at the corresponding Beogram 8002 circuit:

Here, the resistors are on a small board attached to the sensor located under the sub platter. We also see that the value of R46/R2 changed and that R47/R3 carries an "X" now, indicative for the somewhat "semi-exploratory beta release approach" applied for these boards (I do not know of any consumer product that has so many different versions and slight undocumented changes than these B&O circuits). I think the X is a sign that they used different IR LEDs and photosensors during the production run of these turntables. 

Anyway, lets have a look at the two sensors as they are mounted in the Beogram:

Again, first the old style setup: Front

 and back:

And now the newer type with the added circuit board:

You can see the two resistors on the front of the board. The upper one is for the IR LED and the lower one for the sensor:

This is how it looks from the back:

Due to this difference the main board needed to be modified for the new sensor version. This shows the relevant square inch of the board configured for the old style sensor:

Note that R46 (big resistor that is mounted horizontally) is present and also R47 (red red orange 22k on the left, vertical). Now let's have a look at the board configured for the new sensor style:

R47 is simply missing, and R46 is replaced with a jumper wire!

And there lies the danger when replacing boards without checking what sensor type is installed:

When an old style sensor setup is plugged into a board configured for the new sensor like it happened to me, the LED is directly connected to the +15V rail via the jumper wire, which will probably cause it to be super bright for about 1 microsecond and then dark forever. Well, some people say it is better to shine brightly for a brief moment than to be a dull boring light for a long time, but in this case I get to figure out what modern LED can replace the original LEDs...;-).

I suspect the OP240 may be a good starting point since it can be used to replace IR diodes in other spots in this vintage of B&O. We will see...probably another post coming up sometime in the near future...;-).

Anyway, I ended up transplanting the new style sensor along with the newer boards and that yielded a working setup (again). For the sake of documentation I measured the relevant signals in the speed sensor setup:

This is the signal right at the sensor (P4-pin7):

This signal is cleaned up to a square by the opamp IC1 which is configured as a 5V comparator:

The above trace was measured at pin 14 of the opamp. This signal is subsequently divided down (R51/R50) that the micro controller can digest it, yielding this signal at P6-pin 2:

And that is it about the speed sensor of the Beogram 8000!

Beogram 4004 (5526): Final Adjustments and Test Drive with Art Farmer

The restoration of the Beogram 4004 (5526) that I have on my bench has come to an end. Today I did some more work on the hood and then the final adjustments, and then it was time for a test drive with Art Farmer ("Crawl Space" on the CTI label).

The hood needed some more attention after I polished it. The aluminum trim had come off on one side of it. I softened the old glue with a paper towel piece drenched in isopropanol:

After about 30 min the glue came off pretty easily:

I usually glue these side parts with 3M adhesive tape:

After cutting it to size with a razor blade

I removed the protective tape

This tape is ultra thin, i.e. can hardly be discerned. Then I clamped the pieces together:

And after a day of clamping the trim was attached again:

On to the adjustments:

After adjusting the sub-chassis and the platter, and the arms to be horizontally parallel to the enclosure, it was time to adjust the tone arm. First I did the arm lowering limit:

This makes sure the needle misses the ribs on the platter should the electronics malfunction and the arm be lowered onto an empty platter. Then I fixed the counter weight in place. The first step was to replace the flimsy locking washer on the bolt

with a M3 nut and a washer:

This allows locking the counter weight position in place by tightening the nut. Great for shipping a turntable. The next step was to adjust and calibrate the tracking force adjustment wheel:

Most B&O cartridges are specified for 1.2g tracking weight.

The final adjustment was the tracking feedback:

The light intensity trimmer on the Beolover LED light source makes the fine tuning very easy.

After cleaning the aluminum panels and the platter, it was finally time to play this Beogram!

I selected a recent acquisition to my collection, Art Farmer's "Crawl Space" Album, which I prepared for play with a thorough clean with the new CleanerVinyl EasyOne ultrasonic vinyl record cleaner.  Art Farmer recorded this album for the CTI label in 1977. This record has quickly become one of my favorites. Very smooth and melodic. Beautiful trumpet play...another awesome CTI release. What a beolovely sight and sound!:

I will play this Beogram a bit longer to make sure there are no intermittent issues, and then it will be time for it to return to its owner!