Beogram 4000: A New Arrival from Australia - First Look and a Fun Evening Finding a Short in the 6V System

I recently received a Beogram 4000 from a Co-Beolover in Australia for a functional restoration. This shows the unit as received:

Sadly, the keypads were not taped down and so the big one in the center liberated itself on the way. Luckily, soon after it found a safe spot in the guts of the deck where it remained for the rest of the trip.

On the way to its safe spot it made a few small marks on the surrounding aluminum surfaces:

Over all, this Beogram got off lightly from this episode. I have seen units where such awol keys can create a lot of dings. One thing that saved this one is that there was a foam piece under the hood as I show in my packaging video. This reduced the available pathways for this key considerably.

So not too bad. Actually, this deck still looks fairly good with a nice platter (only a few dings on the rim, probably from earlier transportation without locking the transport locks): 

I removed the aluminum panels and the platter and had a look below deck:

Immediately, some 'beautiful' work on the reservoir and motor capacitors became apparent!...;-):

I also found an earlier version of the Beolover Tracking Sensor LED Light Source for Beogram 4000 implemented:

There was also already a new carriage pulley installed:

One of the 'problem areas' of the Beogram 4000 is the awesome position indicator that shows where the needle is on the platter. This indicator has a fragile red plastic part that often gets damaged. I always remove this assembly when I work on a Beogram 4000 to lessen the likelihood for damaging it:

Often the very thin end breaks off when the assembly is removed by inexperienced operators. The thin end is the actual indicator that sticks deeply into the keypad cluster, and so can be broken off easily. In this case, however, the small plastic tab that holds the red plastic part on the metal assembly so it can slide forth and back as the carriage moves had broken off:

I am thinking how to fix this. Maybe a small 3D printed part that can be epoxied on.

After this visual inspection, I re-installed the keypad keys, switched the voltage selector to 110V and plugged it in. I pressed ON and the platter motor started rotating, but otherwise all functions were dead. None of the keys had any effect. No light from the sensor arm either.

This immediately suggested an issue with the 6V system, which powers the early-days hard-wired digital control logic (the 'brains' - one of the exciting aspects of this design!...;-) and part of the analog 'executive' control system of the deck.

I examined the power supply PCB and found a non-standard 500mA/T fuse installed that was blown.

I unsoldered the fuse and measured the signal between the two blue wires that connect to the 6V secondary of the transformer:

This is the trace I measured:

About 32V peak to peak AC. This is about what one would expect. This translates into about 11V RMS, which then is converted by the old-fashioned analog voltage regulator and a 2200uF capacitance into a stable 6V rail.

The presence of the proper input voltage and the blown fuse suggested a short in the 6V system. And indeed when I measured the resistance from the 6V reed relay output to GND I saw essentially 0 Ohm:

This suggested a direct short somewhere in the 6V system. Previously, I had never fully explored the 6V system on the Beogram 4000. It turned out to be a bit of a 'can of worms' with many yellow wires going to solder points on the main and keypad PCBs. This gets even more complicated since a lot of these wires go forth and back on the boards themselves to bridge circuit traces on the old single layer boards, as well as between the boards to complete circuits. This messy design is a consequence of the limited manufacturing techniques for electronic circuits of the early 1970s, which made such connections necessary.

This left basically only one option for isolating the problem: Unsolder all yellow wires one-by-one and keep an eye on the resistance between 6V rail and GND:

Even the solenoid transistor is connected to a yellow wire (which has nothing to do with the 6V system - I guess they ran out of wire colors...;-). I replaced the transistor anyway during my odyssey through the deck, just to make sure there was no additional source of short circuit (they often go bad due and I always replace them when I restore a Beogram). This shows the original transistor soldered in:

And after installing a modern TIP41C that has a higher voltage tolerance, which is advantageous for its battle with the solenoid sparks:

After a while I finally isolated the short circuit to be somewhere on the sensor arm assembly. Its light bulb is powered by the 6V system and, yes, there is a yellow wire going into the sensor arm assembly!

My measurements led me straight towards the sensor arm tube itself. And indeed this is where I finally found the short:

The person who worked on this deck apparently removed the sensor arm, probably due to a stuck damper to arm linkage, whose pivot point can only be re-lubricated when the sensor arm assembly is liberated. I think he removed the actual sensor arm tube when he tried to get the linkage out, which is usually obstructed by the sensor wiring. Then, when he put the arm assembly back together, he mistakenly installed one of the spiky lock washers that are used for securing the arm assembly to the carriage under the screw that holds the sensor arm tube to the assembly. In this process he managed to get the yellow wire caught by the spiky lock washer, which duly pierced the insulation:

This made me remember a formative moment of my late adolescence, when I brought my first car (a 1969 Renault 4 with 26HP and a 6V battery system...;-) to a mechanic due to a clogged up carburetor. When I asked 'how much', he said, "100 Deutschmark if you let me do it right away, and 200 DM if you try it first yourself"...;-). Sometimes it is just a good idea to let the experts take over. It saves everybody a lot of time.

I set out to fix the damage. This required unsoldering the end of the yellow wire from the carriage PCB and pulling it out so I could install a stretch of shrink tubing:

This shows the shrink tubing installed:

While I had everything apart I also removed the damper to arm linkage and put some synthetic grease on the pivot:

A slight tug on the small copper plate that is glued to the sensor arm assembly to facilitate lateral tonearm movement when the arm is up made it fall off:

I cleaned off the deteriorated double sided tape and epoxied it back into place:

Then I put everything back together.

I installed a new proper spec 400mA/T fuse in the secondary transformer circuit:

I also replaced the 6V regulator power transistor and the two electrolytic capacitors that are on the power supply board. This shows everything back in place:

Before I plugged the unit in I measured the resistance to GND at the output of the 6V reed relay for the record:

I guess when everything is o.k. one should see around 30 Ohms. Most of this current path is caused by the light bulb in the sensor arm. 

I plugged the unit in and pressed ON. Now the sensor arm light came on and I was able to move the carriage left and right and also could activate the solenoid. Life signs!...;-).

Now comes the main part of the restoration! Stay tuned.

Beogram 4000: Installation of a New Precision Machined Solid Teak Frame

I recently received a lovely new CNC machined solid Teak plinth from Christian Hakansson, to be installed on the Beogram 4000 that I recently functionally restored.

Unfortunately, this Beogram had an original plinth that was damaged at the corners (please, watch out for door jambs when you carry your Beograms around!!...;-):

I removed the plinth:

If you do this at home, please, note that there is a 5th bolt under the keypad, i.e. the keypad needs to be removed before the plinth can be extracted. 

The deformed particle board under the veneer suggested that this plinth not only had damaged corners, but also had been in contact with too much moisture at some point in time:

The installation of a new plinth requires that the metal fixtures be removed from the old plinth to be transferred to the new one. I usually wrap the plinth in aluminum foil and then I put it into the oven for an hour at 200-250F. Once it comes out the metal parts can be separated with a suitable spatula or similar:

Once the parts are off, the residual contact cement

needs to be removed. I usually soak paper towel with isopropanol or goo gone and wrap the metal parts in it:

I put aluminum foil around it to prevent evaporation:

After 24 hrs the glue can be rubbed off with the drenched paper towels:

This shows one of the cleaned metal fixtures:

I use ultra thin 3M 300LSE adhesive tape for the installation. This makes the process much cleaner than with contact cement. The tape can be cut out with a razor blade to match the frame shape:

It is important to not cover the little spring tabs that are in the back of the frame:

Otherwise they can get glued to the wood and are not able to perform their duty (holding the plinth in place once it is pushed back) anymore.

Now comes the moment where the metal parts are glued to the wood. This is probably the most difficult task since one only has one try and the parts need to be placed precisely at the right level on the frame. This is greatly simplified by using the aluminum panels of the Beogram. They have the right thickness and can be used to align the metal parts with the frame.

It can be challenging to get the metal parts all the way into the corners since there is adhesive on both sides. I usually deal this issue by using some parchment or wax paper to prevent one side from sticking, while I push in the part all the way into the corner:

This shows one side glued while the other still has the paper in:

Sometimes the metal parts are not entirely conform with the frame in the corners. Many Beograms actually came with this issue 'factory installed'...;-). I sometimes use tongue-and-groove pliers to help seating the metal parts in the corners. Be careful not to damage the frame if you do this at home: 

This shows the new frame with installed metal parts:

And here a couple happy shots of the Beogram 4000 with the new frame installed. Beolovely!!:

Beogram 4002/4004 Keypad Restoration Service

One of our long-term projects has been to come up with a process to restore Beogram 4002, 4004 (and 6000!) keypads to their original state. We made several attempts over the past 3 years to replicate the original process and were met with many failures. Most steel will bend and just stay bent when buttons are pushed/flexed. Most cutting methods cannot create details as thin as the small gap between the keys. The coating is a challenge, to find something durable that has a similar overall effect.

We have finally landed on the best combination of materials and procedures to fully restore the keypads and are now offering this service in the Beolover Shop. Be sure to read this full article for information on what the restoration process is and how to remove your keypad to send it to us.

Many keypads will start off with keys in this condition:

We originally planned on a process to restore/re-coat the original steel plate, but there are several problems with trying to restore the original. The first problem is that if you strip away the old coating, the areas that had worn through will stand out in certain lighting conditions, even when they have been re-coated. The second problem is that you will likely have some waviness in the material from the extraction process, the glue especially in DC models is very tough and the plate can easily get bends where you don't want them. The third problem is that if anything doesn't go perfectly, you have no backup plan. Below is an extreme example after the coating was stripped, there is waviness everywhere:

Now that we have new keypad plates, we don't have to think about the originals, which is quite a relief. There is no difference between the original keypad with a new coating on it and our new keypad with the same coating. There are minor differences between the new coating and the original coating, which we feel are worth it for the quality of the coating. Below on the left is an original in very good condition, on the right is a restored keypad with a brand new plate (more photos in this post).

How to Remove Your Keypad

In order to send your keypad for restoration, you will need to extract it from your Beogram. All that is needed for this is a flathead screwdriver for the single screw that holds the keypad in place. The process is easy, anyone can do it (takes 5-10 minutes). The first part of the removal process is also discussed in the Beolover Commander installation video (from 0:45 to 2:15). The Beolover Commander product is highly recommended to extend the life of the restored keypad.

1. Unplug the unit and hold the start key to drain any remaining power.

2. Carefully remove the stylus cartridge, taking care not to touch the stylus/needle/cantilever. Store in a safe place!

3. Slide the wood plinth forward to unlock the top plates. If it does not easily slide forward, locate the two black metal tabs at the back inside edge of the plinth (see photo below) that may need to be carefully nudged outwards while sliding the plinth forwards. These tabs are between the case and the plinth on each side.

4. Carefully begin to lift the right side of the right cover plate, taking care not to scratch the paint on the case or the keypad display module. Underneath, it is secured by a copper U-shaped piece and the left edge is tucked under the platter surround plate. Once it is slightly raised, it should slide out to the right.

Note: when re-installing this top plate, it is sometimes necessary to lift the top right of the platter surround plate so that this plate can slide back into the copper support pieces. Some earlier models have two pegs on the keypad module that this plate plate aligns with.

5. Lift the platter surround plate out, taking great care not to damage the case, the platter or the plate itself.

6. Place a cloth on top of the platter and carefully lift the gauge/display module out of the keypad by rotating it backwards slightly while pulling up on it gently. It should click out of place, then you can rotate it to the left and place it upside down on top of the platter.

7. Under the display module you will find a single flathead screw that holds the keypad in place, use a screwdriver to remove it.

Note: When you get your keypad back and have to replace this screw, it can be a little tricky to find the screw hole on the case, it will require a moment of patience as it is on the other side of the audio output board which may not be perfectly aligned with the hole as it moves around.

8. Lift the keypad gently, if you have a DC (551x/552x) model then you can disconnect the keypad harness from the main board. For an AC (550x) model, place a piece of paper or cardboard underneath the keypad as we will be removing the circuit board and don't want it touching the case or audio output board.

9. On back side of the keypad module, locate the triangular copper shape at the top center of the circuit board and lift it slightly so that the pin at the top is above the keypad frame, then slide the board sideways out of the keypad (and for AC models, let it rest on the cardboard/paper you placed previously).

Your keypad should now be free from the unit and ready to mail to us. It is best to use a 8x8x4" box and some foam padding if possible, though there are many ways to pack it safely.

Our Restoration Process

Each keypad sent to us will go through the same procedure to restore it. The first step is to warm up the keypad, to a level that will not affect the black paint of the screen printed lettering, but will loosen the glue and make it easier for us to remove the original pad and back pieces. Once it is warm, we can start with a large flathead between two of the keys, a small turn and they will break loose:

Lifting the original steel pad is challenging, especially on DC models where it can be very stubborn, eventually it will let go:

Nest, we have to clear all the old glue:

We re-paint the black edges under the keypad:

Optionally, upon request, we can also take this time to paint the area below the keypad so it cannot be seen from above when looking down at the Beogram:

We then use high bonding strength adhesive on both the keypad frame and the steel pad and join them. Here is the new keypad plate before it has been glued down:

Replacement Back Pieces

The last step is to install the back pieces. The original back pieces are not ideal for several reasons. One reason is that they are not quite thick enough, especially the 550x models which have 2.85mm back pieces. The later 551x/552x have 3mm back pieces. The original pieces have a tendency to "pull the keys down" below level, here you can see an original keypad - exactly as B&O left it; the START key (and all the other keys) are actually "below" the level of the sides:

We wanted to fix this so the keys would always be level and so we could use a consistent-level high bonding strength adhesive tape, rather than contact cement (which introduces variability to the level). We have created new back pieces which are 3.15mm thick and leave the keys perfectly level every time:

We were also able to reduce key travel slightly so that the buttons are closer to the electrical contracts. The new back pieces are made from black nylon and look like this (not that anyone will ever see them!):

Optionally, upon request, we can return the keypad without any back pieces installed if you wish to glue the originals back.

Finished!

Once you receive the keypad back from us, simply follow the keypad removal steps in reverse. The final product, once installed in your Beogram: