Beomaster 6000 (2702) restoration: broken FM dial wheel shaft bearing

When dismantling the Beomaster 6000 quad, I already noticed a damage to the ball bearing inside the shaft/bearing house of the FM dial wheel. The retainer clip was also missing and the 3mm nut was the wrong one. It needs to be a self locking nut. So time to start fixing this.

I guess the bearing got damaged while trying to remove or fix the (missing) retainer clip. It looks like someone pierced hard with a screwdriver on the metal shielding of the bearing. It turned out to be hard to remove the shaft as well due to some light damage to the end (where the retainer clip sits). Some force had to be used to tap it out.

The ball bearing is a SKF 625R type. The R stands for a low friction one sided metal dust shielding. The other side is open. That allows to put some (silicone) grease in it.

All is good! Another issue fixed. Up to the next one...

Beogram 8000: Repair of Platter Brake Circuit

After replacing the electrolytic capacitors of the Beogram 8000 that I am rebuilding right now and fixing the scraping subplatter issue the unit was again functional and ran smoothly at 33.33 RPM. However, I noticed that after pressing stop and the return of the arms to the home position the platter continued to spin for a long time until it finally came to a rest. The 8000 has a low friction bearing and there is no belt due to the linear platter drive. So there is very little friction overall once power is cut to the motor stator coils. That is why the designers of the Beogram gave it a motor brake that reverses the motor phases to essentially run it in the opposite direction for bringing it to a fast stop. That makes the humming noise when the platter comes to a fast stop.

This shows the relevant portion of the circuit diagram as shown in the Technical Product Information manual:

The motor stator coils are OL1. This are the two big coils that 'hug' the sub platter (which is the rotor of the motor). These coils are phase shifted by the motor cap 4C1. This is basically the same setup like in an AC motor 4002. The motor is driven by the Drive System, which is essentially a push-pull stage that follows the grid frequency taken from a dedicated transformer coil (4T1A) and which regulates the current through the stator coils that is produced by transformer winding 4T1B (the winding shown above the stator coils in the above schematic).
The brake circuit is is essentially formed by TR 31, TR32 and TR33. Once pin 37 goes low, TR31 is turned on (and the drive system turned off via TR27 and TR28). In the process TR32 turns on which then via D39 pulls down the base of TR33. TR33 turns on and the positive half wave of the 60Hz signal from the 4T1B winding is fed into the opposite end of the left coil of OL1 via D40. This reverses the motor phase relative to the normal signal.

The 'reverse drive' aspect of the brake system can be seen by a simple test: Connect the base of TR31 to ground with the unit in standby and the platter starts spinning backward!

It turned out that the brake malfunction in this unit was caused by a broken trace. The trace that connects the collector of TR31 to R110 was cut through, probably the consequence of a previous 'repair' attempt. This broke the chain of command between TR31 and TR32, so when the microcontoller said "brake!" TR32 did nothing, and TR33 remained off, which prevented the reverse phase signal to be applied to the stator coil. Since power to the coils was still cut via TR28, the platter simply spinned until mechanical friction finally stopped it...

Below is a photo of my fix: I soldered a small piece of 'magnet wire' between the relevant solder spots: Magnet wire is good for such tasks since it is coated with a special polyurethane coating (so one can wind a magnet without making short circuits between the windings) that burns off when touched with the soldering tip. Very convenient for making connections with short pieces of wire where it would be difficult to take the insulation of mechanically with a stripper tool.

After this repair the unit 'fired on all 8' again (ah the good old days when most real cars had a V8!)

On to mechanical adjustments and fixing the cosmetic issues of this unit!

Beogram 8000: Repair of a Scraping Sub-Platter with a 3D Printed Insert for the Main Bearing

The next item to look into with the Beogram 8000 that I am restoring right now was that the sub-platter scraped along on the chassis. This shows the interior of the 8000 with the sub platter still in place:

Somehow the platter was situated a few 1/10ths of a mm lower than usual, which made it touch the sub-chassis base plate in a few spots. This prevented the deck from maintaining a constant speed (it never showed 33.33 on the display, just 33, which is a signal that the RPM is off). Also it made an intolerable mechanical noise. Far from Beolovely! 

This seemed strange to me (there is no way to adjust platter height like one could in a Beogram 4002) and so I poked around a bit on the internet. I came across an uttering by one of the greats in this business, Dillen of Beoworld: "Typical symptom of a broken main bearing nylon insert. It happens often if the Beogram was transported with the heavy platter mounted or just put down too hard." (my customer confirmed that the ebay seller did not take out the main platter when he/she shipped it to him...).

He went on to say "The whole weight of the platter, hub and sub-platter rests on the very sharp pointy tip of the hub spindle. Only fix is to replace the nylon insert."

This shows the spindle after lifting out the sub-platter:

In the pic the tacho sensor is already out of the way (it swings away by moving the brass lever clockwise). In that position one can pull out the spindle:

The picture shows the pointy end of the spindle that rests on the plastic disc that Dillen mentions in his post.

The plastic disc can be pushed up using a small hex wrench or similar (there is a small hole on the bottom of the bearing that can be accessed from underneath the enclosure. This shows the white plastic (probably nylon) insert in the main bearing:

And after pushing it up:

First I tried to simply flipping it around, but there is no indentation on the back of the plastic part for holding the spindle in the center of the bearing. So my idea was to simply shimming the insert up a bit to lift the platter back to its normal height. The insert still seemed in decent condition, only the indentation was a tad too deep after the incident, causing the platter to be too low. 

I designed a small disk that I printed with my 3D printer:

After a few tryouts with different thicknesses it turned out that 0.7 mm was a perfect thickness to raise the platter just enough to not scrape anymore (test with the main platter and a record on top if you do that at home...).

The disc is easy to insert when the insert is up sideways:

Once the printed disc was next to the insert, it is straight forward to push the parts back to horizontal and down into the bearing.

Once I installed the spindle and the platter again, everything was fine. No more scraping, and the platter turned freely.

Beogram 4002 (5513): Infusing Oilite Brass Bearings of DC Motor with Oil Under Vacuum

One of the challenges with restoring DC motor Beogram 4002/4 Types (551x and 552x) is the restoration of the motor itself. Most of the DC motors present themselves with loud running noise and/or strong RPM variations at this point in time. It turns out that simply taking the motor apart and lubricating the brass sleeve bearings with grease is only a temporary solution.

The bearings used in these motors are 'oilite' brass bearings (see a recent thread on Beoworld where Dillen hinted at this). Such bearings are infused with oil after manufacturing. The brass is porous, and therefore oil can be 'inserted' into the metal itself via a vacuum based infusion process. This results in light duty bearings that can run without the need for external lubrication. However, over time the oil is slowly depleted from the bearing metal (and probably distributed inside the motor). Once the oil is gone and the bearing dry the noise issues and RPM variations start occurring.

The restoration of the bearings requires to infuse fresh oil into the metal. Unfortunately, one has to completely disassemble the motor to get to the bearings (one can force them out without disassembly, but it is impossible to get them back in...).

Here are a few impressions of the process. This shows the motor disassembled:

The two bearings are actually different:

The bottom bearing is shown right with its plastic support washer next to it. The top bearing is on the left. It is slightly bigger.

The infusion process can be done with SAE 30 motor oil and one needs to pull a vacuum in order to suck the air out of the pores of the brass volume to make room for the oil that it can diffuse in by means of Brown's motion. I did this with a FoodSaver vacuum sealer unit that came with an attachment for Ball mason jars. Here is an impression of the bearings in the oil under vacuum in the jar:

As soon as the vacuum is applied small air bubbles arise from the bearings. They accumulate on the surface of the oil as seen in the photo. It is interesting to note that the top bearing produced considerably more bubbles than the bottom one. This is probably a result of the higher friction seen by the top bearing due to the belt torque applied to it. After about six hours the bubbling pretty much stops and the bearings are ready for re-installation.

This is where it gets a bit difficult since the top bearing is held in place with a metal ring that is fixed in place with tabs that needed to be bent up to get the bearing out. It can be difficult to get the tabs bent back far enough to ensure a snug fit of the bearing in its fixture.

I designed a 3D printed tool to simplify this process:

The red cylinder goes inside the motor housing to hold the ring in place:

Once the ring is pushed up all the way the tabs can be bend slightly with pliers:

the final press fit of the tabs into the small recesses is then done with the top part of the tool and adjustable pliers against the red bottom part:

This results is a pretty tight fit almost as good as before disassembly:

I am planning to make a video about this process. But for now it is time to test this motor for 24 hrs using my BeoloverRPM device:

33.33! So far so good! Let's see how this motor feels about things tomorrow!

Beogram 4002 (5523): Adjustment of Platter and Sub-Chassis Alignment, Installation of New Transport Lock Bushings and Adjustment of the Tonearm

After restoring all mechanical and electronic functions of the Beogram 4002 (5523) that I am currently working on it was time to give this baby a spin, and for that I wanted to have platter, sub-chassis and tonearm perfectly aligned to specifications. I started out by aligning the sub-chassis to be in the center of the transport locks. It turned out that a previous 'specialist' had installed the transport locks in a wrong way by not aligning the 'feet' of the lower locknuts with the matching cavities in the cast enclosure bottom. This prevented me from doing the adjustment. While I had everything apart I also put in new bushings since the original ones were completely deteriorated as indicated by the many pieces of orange plastic debris throughout the enclosure:

This shows the left lock with missing bushing:

This shows the new bushings installed in the left transport lock:

and here in the front lock:

There is a video about installing new transport lock bushings in my Beogram 4002 playlist. The bushings can be ordered directly from my Shapeways store. This is the link to the part. Two are needed per transport lock since one half is installed from the top and the other from the bottom.

After rebuilding the locks I was able to do the adjustments. There are two videos on my YouTube channel that show how to adjust the platter bearing and the subchassis (in a Beogram 4000, but the process is very similar in the 4002). This shows the Beogram after the procedure. The platter is flush with the surrounding aluminum panels and the platter is also centered within the main panel.

The final step was to adjust the arm lowering limits and then the tracking force. There is another video on my youTube channel that shows how to adjust the lowering limits. This is a very important procedure since the control system of the 4002 cannot guard against photosensor failure in the sensor arm. If the sensor fails the arm will be lowered whether there is a record or not, possibly endangering a very expensive cartridge. The correct adjustment of the arm lowering limit can prevent stylus failure if that happens.

The final step is always to adjust the tracking force to specifications. There is yet another video that shows this process. Here are a couple of impressions. I always start out by replacing the flimsy locking washer that holds the counterweight adjustment screw in the back of the arm assembly with a M3 nut and a washer. The original setup is way too wiggly for my taste and virtually guarantees that the adjustment changes whenever the turntable is moved. Not good for shipping at all. This shows the original setup:

and here after installing the nut and the washer:

this allows to reliably lock the zero force adjustment in place, which results in a stable weight scale reading on the small adjustment wheel.

After putting in the nut I adjusted the counter weight to yield 1g when the adjustment wheel is adjusted to 1g. This is better than adjusting the weight to yield zero for zero setting, since the adjustment wheel is not fully linear in its scale. Since most cartridges are in the 1-1.25 g tracking weight range, it is good to use 1g or 1.2g as center point for the calibration.

Then it was time to adjust the final setting with my B&O tracking force gauge:

and then it was finally time for some bliss: Playing one of my favorite records on this deck: Yellow Fields by Eberhart Weber on ECM.

Beogram 4002 (5521): Rebuilding the DC Motor

I started working on the Beogram 4002 that recently arrived. When doing my initial assessment, I noticed that the DC motor has completely dry sleeve bearings and so every time it would turn on without the belt and platter installed, it would emit a shrill noise due to the high RPM without a load. So this had to be fixed first. There must be peace and quiet in the Beolover's lair (and some nice vinyl playing while I do my work...;-). Here are a few pictures taken during the process. this shows the motor in-situ:

After removing the mounting plate, unscrewing the two screws that hold the motor to it and removing the glued on pulley (this may require some carefully administered force with a large screw driver to pry it off), I opened up the outer enclosure and extracted the motor:

Then I opened the motor up by removing the bottom shell that contains the brushes and the feedback coils:

Nice classic design! Then I extracted the rotor after removing all glue remnants on the shaft (this is important since otherwise the shaft gets stuck in the upper sleeve bearing and then damage can ensue:

Once at this point, all that is needed is to clean the commutator and the brushes with a fiberglass pen, lubricate both bearings with some silicone grease and then put everything back together in reverse. Note that it is crucial to make sure that both brushes are fully inserted onto the commutator before closing the motor back up. The pulley needs to be glued back on, too. Super Glue Gel works nicely. 

I did all that and installed the motor, and now it spins very quietly. Time to enjoy some vinyl! (just ordered an original 70s pressing of Miles Davis' "E.S.P", one of my favorite jazz records of all time)! - let's see if my vinyl record cleaner can salvage it...I really started liking using it...;-)

Beogram 4002 (5513): Lubrication of Platter Motor Bearings

Today I lubricated the bearings of the DC motor of the Beogram 4002 (5513) that I am currently restoring. This shows the motor after extracting it:

This brushed commutator motor has simple sleeve bearings. To get at the bearings, the first step is to take the pulley and the outer housing off. It is a good idea to make marks to remember later in what orientation the bottom plate was mounted to the motor. The pulley is glued to the shaft, i.e. one can simply pull it off. After taking off the two small screws the housing can be opened,

and the motor extracted:

After removal of the black rubber vibration insulation boot the circuit board that connects to the brushes is visible:

After marking the position of the bottom part, the three screws that hold the bottom part can be removed, and the brushes plate pulled off:

This shows the two halves in more detail:

The bottom bearing can be lubricated by putting a dab of silicone grease into the bottom sleeve below the brushes. The top bearing is best lubricated by simply put a bit of grease on the shaft and pushing it up and down through the bearing a few millimeters. After application of the grease, the motor can be reassembled. The commutator is fitted with a slanted plastic disc that pushes the brushes apart and guides them on the commutator while the plate is inserted. This is very convenient and protects the brushes from being bent out of shape. After that simply track back the disassembly steps. Once the motor is back in its outer housing the pulley can be glued back on the shaft with superglue gel. And that is it!

Beogram 4002 (5513): Replacing the Tracking Sensor Light Bulb with a Plug-In Ready SMD LED Assembly

Yesterday, I installed my latest version of the SMD LED light source for the tracking sensor of the Beogram 4002 (5513) that I am currently restoring.

A while ago I developed a drop-in ready SMD LED based assembly for replacing the incandescent bulb fixture. While this worked great, it still required the application of the inconvenient original tracking sensor sensitivity adjustment process. The mechanical positioning of the light sensors relative to the light source is quite tricky, and it is always chore to get this adjustment precisely right. The reason for this is that the mechanism is quite sensitive, while the adjustment mechanism is pretty coarse, requiring a lot of trial and error to get the adjustment right.

A recent beolove-affair with a Beogram 4000 taught me a better way to get this adjustment right: Add a trimmer potentiometer to the LED circuit, which allows the adjustment of the intensity of the LED. This gives an additional adjustment parameter that enables a straight forward fine tuning of the tracking response. I liked this a lot in the 4000, so I adapted the approach to the 4002's higher bulb voltage.

I made a short video about the installation and the tracking response adjustment process for this new design:

Here are a couple high-res pictures of the new LED assembly. I will be happy to provide this part to other enthusiasts!. This shows the added trimmer:

And this is a shot of the bottom side. The LED is in the same spot as the filament of the original light bulb assembly. The body of the replacement part is 3D printed and has the same shape as the lower part of the original fixture. This ensures a precise fit onto the light sensor assembly below the aperture:

This shows the part installed:

Beogram 4002/4004 (5513): Adjustment of the Platter Bearing

I continued working on the Beogram 4002 (5513) that I am restoring right now. This post reports about adjusting the platter height and tilt. When I received the unit, the platter was at the wrong height and also had significant tilt. The procedure with this model is similar to what I show in the video that I made about this process on the occasion of a Beogram 4000 restoration, but the bearing mount is different in the 5513 type, so I made another video. The key difference between the later 4002/4004 and the original 4000 bearing is that the bearing is now mounted on a tripod plate. Please, watch the video for details of the process. It shows how to do measure the platter alignment and how to adjust the bearing. Enjoy!

Beomaster 6000 Quad: Speaker Jacks Replacement

Finally I received the package from Martin/Dillen of Beoworld (thank you!!) containing light bulbs and speaker jacks for my Beomaster 6000 4-Channel. The speaker jacks for the front channels were unfortunately broken out, i.e. I was so far not able to test the front channels for fear of creating short circuits etc.... Here is a pic of the broken out jacks before replacement:

The exchange is not too difficult. I removed the six screws that hold the panel with all the jacks. This allowed me to pull the panel up by a few cm. This made it easier to access the solder tabs of the jacks.
After unsoldering the connections the jacks came out, and I replaced them with the new ones. Here a couple of pics of old and new: These are the old ones:

The problem with these jacks is that they originally relied on some degree of stress between the plastic wings and the metal panel to seat them snugly. Over the course of 40 years unfortunately the plastic becomes brittle and the wings break off, which causes the jacks to be pushed into the enclosure when plugging in a plug. Anyway, here the replacements:

Beautiful! Here is a pic after inserting them into the slots:

And after attaching the filters and leads:

After this procedure I plugged in speakers, and lo and behold the front channels also seem to work!!
This is good news. It appears I really may not have to take the entire thing apart for now!