Beogram 4002 (5513): Non-Working End Groove Detection - Repair of a Detached Carriage Position Sensor

I am almost done with the Beogram 4002 (5513) that I am restoring right now. One unusual issue with the unit was the detached carriage position sensor:

The sensor is in the black light shield that is seen 'hanging' at an off-angle. It needs to be vertical that the black sections on the plexiglass 'ruler' that is attached to the carriage can properly block the light coming from the IR diode that is behind the ruler. If the sensor is not close to the ruler stray light can enter causing instabilities in the carriage operation. In this Beogram this manifested itself by a non-working end groove detection. This particular mechanism is especially dependent on a proper positioning of the sensor since the mechanism depends on the step-wise charging of a capacitor until the 'STOP' function can be triggered. If the light is only partially blocked by the narrow end groove detection bars on the ruler the charging mechanism only works partially which can cause the voltage build-up on the capacitor to be too low.

I removed the carriage position PCB:

The sensor is seen detached from the double sided tape underneath. The IR diode sits right in front of the sensor, which is behind the narrow slit in the black housing.

I glued the sensor housing back on with a bit of epoxy and held everything together with a carpenter clamp until the glue bonded:

This shows the sensor after removing the clamp:

Then it was time to reinstall the board:

Now the end groove detection worked again. It is interesting to note that the other functions were working properly even with the detached sensor...

Beogram 4002 (5514): Rebuilding the Arm Lowering Mechanism and the Tracking System

This Beogram 4002 (5514) had a completely stuck arm lowering mechanism. The lubricants had hardened to a degree where I needed to use a screwdriver to pry the linkages from their pivot pins. This is a frequently observed phenomenon, which is easily fixed by cleaning and lubricating the mechanism. This shows the solenoid and damper with linkages before I took everything apart:

This shows the parts spread out on my workbench:

This video shows how to rebuild the tone arm mechanism in detail. After putting the mechanism back together with fresh lubricants, I moved on to the damper to arm linkage. This shows the arms from the back. The linkage sticks out in the back under the yellow paint  marking:

To lubricate its pin the sensor arm needs to be extracted:

This linkage was also stuck and it can off including the pin on which it pivots:

After separating the pin from the linkage I glued it back in with a bit of epoxy and then reinstalled the linkage with a bit of silicone grease. This video shows how to get to the damper to arm linkage and re-lubricate it. Then it was time to put the sensor arm back in and align the arms to be parallel to each other and perpendicular to the carriage rods:

This concluded the restoration of the arm lowering mechanism, allowing me to move on to the tracking system. I usually install my SMD LED based light source to replace the original incandescent bulb assembly, which is not available anymore. LEDs are very long lived, so this promises trouble-free carriage operation for a long time.  I also replace the usually wobbly and/or cracked plastic carriage pulley with a precision turned aluminum unit, which can be had from Nick of Beoworld. I'll be happy to get other aficionados in touch with Nick, just send me an email. This shows the original parts in place:

After removal of the original bulb housing the tracking system aperture is visible:

This shows the 3D printed replacement part together with the original bulb housing:

My part has an integrated intensity trimmer, which enables a straight forward fine tuning of the tracking feedback sensitivity.

Here is an impression of the installed parts:

Pretty, isn't it?? I will adjust the tracking system sensitivity after I rebuild the PCBs.

Beogram 4002 (5513): New Transport Lock Bushings and cabinet Guidance Washers

Like so many, the Beogram 4002 (5513) that I am rebuilding right now had lost its transport lock bushings, and also all cabinet guidance washers needed replacement (someone replaced them prior with regular washers, which of course does not do a good alignment job in lateral direction). It is important to realize that a proper platter and arm alignment can only be done if the transport lock bushings are in place and the plinth is in alignment with the metal enclosure. If these items are not take care of before, the platter alignment can only be regarded tentative and would not survive transport.

This shows the front transport lock as I found it:

The bushing is completely missing. 

This shows the mechanism taken apart with the lower part of my replacement bushings installed already:

Add the top part:

My two-part design enables installation without having to take the entire sub-chassis out. 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. You will need two per transport lock.

This shows the reassembled mechanism with the new bushing in place:

the next step was to replace the cabinet guidance washers. This shows the left-back one as I found them. A number of the 4002s came with acrylic guidance washers and they usually crack in two halves. In this car someone replaced them with standard washers, which at least holds the plinth down. But it neglects the secondary function of these washers to actually guide the plinth in lateral direction, giving the slide mechanism an entirely different feel

Anyway, I replaced all five of them with my 3D printed nylon replicas from Shapeways:

There is a video about this procedure in my Beogram 4002 playlist. The guidance washers can be ordered directly from my Shapeways store. This is the direct link to the part. You will need five (there is one beneath the keypad, only visible once the keypad is removed).

Here is an impression of the right-back washer. Notice the lovely aluminum carriage pulley in the background, which was supplied by Nick from the UK (I will be happy to get you in touch if you would like to order one):

The next step is the platter and sub-chassis alignment. We are getting close to a test drive of this beauty!

Beogram 4002 (5513): Repair of Misaligned Plinth Corner

Another cosmetic item that needed fixing in the Beogram 4002 (5513) that I am currently restoring was a cracked plinth corner whose repair was botched earlier. These plinths often separate at the corners as the glue ages. It is not too difficult to glue them back together with white wood glue such as Alene's. Unfortunately, the right corner had been glued together without properly aligning the wood pieces:

Also, there were glue traces all over the veneer surfaces, very visible under certain viewing angles. First I thought I would have to slightly sand the surfaces to get rid of them, but luckily using Mr. Clean Magic Eraser Pads crossed my mind. And this worked great. What would we do without Mr. Clean!...;-).

Unfortunately, the misalignment also required the removal of the metal fixtures that are glued to the wood frame, since they were also glued on in wrong alignment:

Once everything was apart I glued the parts back together, aligning them on a flat surface and securing them with carpenter clamps until the glue dried. This is the final result:

How pretty together with the newly rebuilt keypad! This is Beolove!

Beogram 4002 (5513): Keypad Restoration and LEDs for the RPM Indicators

The Beogram 4002 (5513) that I am restoring right now came with a pretty badly worn keypad. Unfortunately, the keypads are a weakness of this design since their surface does not respond well to the presence of fatty acids deposited from the user's fingers over time.

Sadly, after a long illness my friend in Denmark, who in the past restored these keypads for me, passed away recently. May he rest in peace in B&O heaven.
Over his last few months he taught me how he does it. I started practicing to fix them a couple months ago, and finally I achieved one good outcome. It is a pretty difficult process, and I would say I am not quite reproducible yet with it, but it worked once so far:

This picture shows the original keypad of the Beogram on the left. It has severe usage marks on the most commonly used keys. On the right is the one that I was able to restore. It looks quite original, I think. Now let's see if I can do it a second time...

While I had the keypad out, I also exchanged the incandescent bulbs in the RPM scales with my LED replacement boards. This shows the original bulbs:

And replaced with my SMD LED boards:

These assemblies are available to other enthusiasts. Just send me an email. This video shows how to install them.

On to repairing the cracked plinth!

Beogram 4002 (5513): Rebuilding DC Motor with Oil Infused Oilite Bearings

After replacing the RPM relay and the RPM trimmers of the Beogram 4002 (5513) with modern components, it was time to give the DC motor some TLC. The DC motor can be the most tricky part of a 4002 restoration and it is virtually almost always necessary to do it. The main difficulty with the motor restoration are the Oilite oil infused brass sleeve bearings that are used in this motor. They come with 'oil built in' when the motor is new. Within the typical consumer engineering time horizon of 10-15 years, such bearings can be regarded as 'maintenance-free'. However, on the 'Beolove Time Scale' (BTS) this is of course not a long enough period, and so the oil needs to be replenished. This can be done by removing the bearings and immersing them in oil under vacuum. The vacuum serves to expand the air that over time replaced the oil in the bearings. This draws it out to be replaced with fresh oil.

The first step is to disassemble the motor. This shows the motor opened up:

Once the motor is open, the bearings need to be extracted, and this means to pretty much completely dismantle the motor:

Once the bearings are out, it is time to do the vacuum infusion process. This shows the bearings in a mason jar under SAE30 oil immediately after pulling a vacuum with a FoodSaver pump:

Air bubbles emerge from the bearings. The larger top bearing (left) usually emits more than the bottom bearing (right). I think this has to do with the fact that the top bearing sees more torque over its lifetime due to the belt bearing on it directly. And that probably causes more oil to be extracted from the bearing due to the closer contact.

After 12-24 hrs or so the process more or less stops

And that is the sign that the oil has been replenished. Now the bearings can be reinserted:

The top bearing is held in place by a lock ring that presses the bearing mount up against the motor housing. This ring needs to be pressed firmly against the motor housing in order to re-bend the tabs that clamp it in place. I made a 3D printed mounting tool that allows the use of adjustable pliers to apply even pressure across the ring and in the same time bend the tabs back into place one by one. 

This shows the top bearing re-inserted with the tabs bent back:

The bearing needs to be snugly in place. Test it with a tooth pick. If it can be moved, but there is some noticeable resistance, then it is correctly installed.

The next step is to put the motor back together in a way that it can turn freely and runs in the right direction. The direction depends on the orientation of the bottom plate. The screws that hold the bottom plate to the main enclosure allow three orientations. Only one is right (hence, it is a good idea to make a mark before taking the motor apart...;-). Once the motor turns in the right direction one needs to make sure that it spins at the lowest friction possible. I came to the conclusion that measuring the current while testing it is a good way to assert that everything is o.k. The lowest current achievable is the best alignment of the motor housing relative to the rotor. I usually can achieve ~20-30 mA at 5V when the motor spins freely:

If the current is higher, then the bottom plate needs to be adjusted by playing with the three mounting screws. I usually torque them in small steps in sequence while going around a few times, as you would tighten a vacuum flange.

Once the screws are tightened, the second enclosure can be put back on and then it is time to test the performance of the motor with my BeoloverRPM device for 24 hrs to make sure that everything is really Beolovely! 

Here is the test result for this motor:

The black curve was measured before the motor rebuild. Not too bad as far as original condition DC motors go these days. The casual listener would probably even miss the RPM drop spikes. Usually, these are much more pronounced when people complain about varying RPM in Beogram 4002s. But of course the presence of these spikes means that the bearings are close to the end of their lifetime and that bigger drops would have surely started to occur in the near future.

The red curve was measured after the bearings procedure and also reflects the new RPM relay and trimmers. No more spikes. Of course there is still some variation over time, but those mainly have to do with temperature drift...the price of having a 1970s analog control system.

Beogram 4002 (5513): Rebuilding the PCBs

After restoring the arm lowering and tracking systems of the Beogram 4002 (5513) that I am restoring right now, it was time to rebuild the electronics and the platter drive. I usually start out with replacing all electrolytic capacitors on the PCBs with new Japanese 105C grade capacitors. To get the DC motor to run properly without RPM fluctuations it is necessary to also update the RPM relay with a modern encapsulated unit as well as installing 25-turn precision trimmers for the RPM adjustment. Here are some impressions:

This shows the main PCB in original condition. The red and blue components are the capacitors that needed to be exchanged:

After exchange of the caps, the RPM relay and the RPM trimmers:

And a detail shot of the 'RPM section':

I used my relay breakout board to fit the modern SMD relay. This part is available to other enthusiasts. I also have a version that can replace the National relays that are found in some versions of the 4002.

While I was at it, I also did the output PCB (#8), which was also a good occasion to replace the worn out key pad with a pristinely rebuilt unit...more about that later. Here is an impression of the original PCB#8:

And after rebuild:

It is a good idea to replace the original output relay as they occasional get stuck on one channel and thereby turn the deck into a mono record player. Not very Beolovely! 

I also installed a switch that allows the connection of system and signal grounds. Connecting them can help suppressing grounding issues.

The next step will be to rebuild the motor by re-infusing the Oilite brass sleeve bearings. Then the platter drive should be in a great condition.