Beogram 4002 (5503): New Monolithic Beolover Carriage Position Sensor for AC-Motor Beogram 4002 (Types 550x)

A little more than a year ago I designed a replacement part for the carriage position sensor PCB in DC platter motor Beogram 4002 and 4004 (Types 551x and 552x). This board takes the guesswork out when the carriage position sensor does not work properly. The original design is fairly sensitive to the alignment between the IR diode and the photoresistor, as well as the alignment of the ruler relative ot the sensor, and it can be tedious to get everything properly adjusted.

The Beolover Carriage Position PCB for Beogram 4002 and 4004 (Types 551x/552x) is based on a modern monolithic IR photo-interrupter and circuitry that generates a clean and precise digital output signal for driving 1TR17 on the main PCB.

Sadly, this solution only works in the later DC motor Beograms. The earlier Beogram 4002 with AC platter motor has a much more complicated hard-wired carriage position sensor PCB that is not very easily replaced. But when I recently restored an AC motor Type 5503 Beogram 4002, and it gave me grief with detecting the runout groove reliably, I thought it would be nice to have a solution for these models, too!

Since replacing the entire board is complicated and unnecessary, I designed a replacement for just the sensor part of the board. I designed a board that simply piggybacks onto the main PCB, replacing only the original sensor bulb and photoresistor. This board adapts the same reliable circuit that I used on the DC motor PCB. 

This shows the final version of the Beolover Carriage Position Sensor for Beogram 4002 (Types 550x):

Let's see how it is installed:

This shows the original setup. The photoresistor is in the black housing in front of the 'plexiglass ruler' bolted to the carriage assembly:

After removing the two screws that hold the ruler assembly in place, it can be removed. This reveals the black bulb housing under the ruler.

Here is a view from a different angle (I already had the orange capacitor and white solenoid resistor replaced when I took this photo):

After removal of the bulb cover, the bulb is visible:

The first step for the installation of the new Beolover Carriage Position Sensor for Beogram 4002 (Types 550x) is removing both the photoresistor and the bulb and cleaning the five solder pads indicated below of all solder:

This is best done with a desolder gun since the pads need to be clean and flat so that the Beolover board can be placed onto the original board surface. The board needs to be aligned as shown in the picture below:

This shows it aligned and soldered in place:

When aligned properly, the three round connection vias on the Beolover board are aligned with the respective solder pads where the board connects to power and the base of 1TR17. All that needs to be done at this point is to put a bit of solder inside the vias.

It is a good idea to solder one via first and then adjust the board precisely, while making sure it is fully flat on the original board surface. If it is not flat or misaligned, it may be difficult or impossible to adjust the plastic ruler for proper function of the position sensor.

This shows the plexiglass ruler assembly bolted back into place. 

Adjust the ruler that runs at a constant ~1mm distance from the front-facing part of the sensor during the entire travel of the carriage.

Flipping the switch in front of the sensor activates the on-board LED:

The LED makes it easy to test the proper functioning of the sensor. It should light up whenever a black bar passes between the legs of the sensor.

After installation of the sensor, the Beogram reliably recognized the runout grooves of all records I played. Beautifully!

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 (5513): Brand New Hood Fatally Damaged Due to Bent Hood Hinges! - Straightening Hinges Out and Installation of Another Hood

I recently restored a Beogram 4002 (Type 5513) for a customer in Florida. This unit also received a new hood, which was procured from the beoparts-shop in Denmark. These hoods are exact replicas of the original ones, i.e. do not have any seams from glueing laser cut plexiglass panels together. They are die-cast like the original ones. Very awesome!

Unfortunately, in this particular case the a strange thing happened: The newly installed hood slightly chafed on the hinge back when closing it. This happened about halfway between fully open and closed. When I installed it I did not really take this issue seriously since it was not very noticeable. I basically put it in the 'in the 70s the manufacturing tolerances were a bit looser than these days' bin and tried to forget about it...;-).

However, blissful ignorance was not an option in this case: After taking his Beogram home, my customer sent me this dramatic picture a few days later:

The hood had spontaneously cracked off one of the hinges. A fracture occurred right at one of the two screws. At this point I thought the chafing was probably the root cause since it put a bit of stress on the hood, but I did not understand what caused the chafing. The metal parts looked perfectly o.k. on first glance.

I sent an email to Martin Olsen who designed these replica hoods and asked him if he knew if something like this had happened before. He answered that "I have an interesting Beogram hood on the bench now from a customer who couldn't make it fit properly. The hood would fit reasonably well one side. At the other side it would sit too high and too far forward, enough to show gaps. Opening the hood, I can see that one hinge buts up against the hinge block as it should, but the other has a gap of 2mm.

I took out the hinges, and they appear to be different, in that they have different angles."

The plot thickened! I removed the hinges from the troubled hood and also the hinges from another hood that I was working at that point on that did not have this issue. This allowed me to directly compare the hinges of the cracked hood with those of a 'normal' hood that did not chafe. This is what I found: Indeed the troubled hood had hinges that had a smaller angle between the two shanks than the normal one. This shows two of them in direct comparison:

It became clear that I needed to bend the bad hinges back into the normal shape. To do this I needed a way to precisely determine when the correct angle was restored. So I designed a 3D printed template that I iterated a few times until it perfectly fit into the normal hinges. The perfect fit was established by being able to put a bolt through the alignment hole that I designed into the block to line up with the hinge pivot point. It is evident that the smaller angle of the chafing hinge prevented the holes from lining up.

I took the bent hinges to the workbench and used a vise and adjustable pliers to open the hinge up a bit.

I carefully bent it by small amounts until I was able to put the bolt through the hinge into the template block:

I did this for the other hinge, too, and then put the hinge assembly back together. One side was lacking the plastic slider block, so I installed a 3D printed replica:

Then it was time to install another one of these awesome hoods as well as a new replica 4002 aluminum strip:

I used my alignment tools to place the strip exactly centered:

And then I bolted the hood to the hinge and glued the strip into place:

And I am happy to report that this hood did not chafe anymore! Beolovely!

Of course I am wondering what may have cause the hinges to deform in the first place. The only idea that came to mind so far is that the troubled hood was opened a bit too far and with a bit of violence. Considering the way the hoods are constructed, this would indeed reduce the angle between the hinge shanks if bending occurred. Treat your Beograms more gently, people! Pretty please?!?!...;-)

Beogram 4000: Repair of a Cracked Solenoid Arm, Replacement of the Damper Gasket and Re-Glueing of a Plinth Corner

After replacing the wiring sleeve of the carriage harness and repair of an intermittent solenoid this Beogram 4000 needed tying up a few more lose ends before it could be sent back to its owner.

I had originally restored this Beogram 4000 in 2020, and back then I was not aware of some of the 'standard issues' that these decks can develop. One item that learned about in the meantime is the damper gasket. They seem to harden and as a result arm lowering can become erratic causing the arm lowering speed to vary due to random air leaks around the gasket.

This shows the original gasket:

And the new replacement installed:

This Beogram 4000 also came with a solenoid lever that has a plastic extension for activating the solenoid switch:

As I learned over the years from AC motor 4002s, where this type of lever is standard, these attachments tend to break off at the rivet that attaches them to the metal part. This one also already had a hairline crack:

Since it can lead to a fried solenoid when this plastic extension breaks completely off I replaced it with a 3D printed part that I developed for this occasion:

Here a shot from the side:

This shows the lever after re-installation in rest position

and in extended position:

It properly activated the solenoid switch.

In 2020 I also had not realized yet that the BC142/143 power transistors often go out of spec over time. This resulted in occasional carriage drive H-bridge failures, which caused some unhappy returns to my bench. Hence, I started replacing these transistors preventatively in my Beogram projects as a standard feature. I still needed to catch up this Beogram in the transistor department. This shows the original H-bridge transistors:

And with new compatible replacements:

I also replaced the rest of the power transistors:

Finally, this Beogram had a plinth corner that came unglued:

I removed the plinth and glued it back together:

Beolovely! This Beogram 4000 is performing very nicely again. Let's hope it will stay away from my bench for longer this time!

 

Beogram 4000: Installation of a Brand New Beautiful Solid Oak Plinth! - Very Beolovely!!

Another Happy Day in the Beolover's life! Recently I received a shipment with two new Beogram plinths from Matt Spangler in Oregon, who is the owner of Vintage HiFi Nut. He specializes among other things in restoring/replacing wood cabinets of vintage HiFi. 

A while ago I sent him each a Beogram 4000 and a Beogram 4002 plinth. Both had been mashed up during shipping due to poor packaging. Unfortunately, this is a common issue since many people underestimate the raw forces in play during the handling of packages in sorting centers and on trucks etc...

Anyway, I received these two plinths back a few days ago. Today I had a look:

The top one is the 4002 type and the bottom one the 4000 type. Wile they look very similar, the metal frames are different in 4000s and 4002/4s due to the different size of the keypad clusters and aluminum plates. Here is a detail shot of the very well defined corners:

The top frame was made from solid Granadillo (aka 'Mexican Rosewood'), while the bottom frame was made from solid Oak. The original hardwoods that B&O used, Brazilian Rosewood and Teak are protected species these days due to over-harvesting, and so one has to use alternative hardwood types if hardwood looks are desired.

B&O did use oak in 'the day' on a smaller number of Beograms, i.e. an oak replacement can be considered 'original'. Personally, I think with wood cabinets one can have a bit of an open mind, and whatever looks great on these iconic vintage designs is great!

This is the sad look of the Beogram 4000 that I received recently:

I bought this Beogram 4000 from a seller in Germany. Unfortunately, despite pointing him to my packaging video, he did not believe in double-boxing and foam padding, and so the unit got mashed up a bit on one corner. The padding he used was less than an inch and so this was almost predictable.

While the right side only came unglued, the left was damaged beyond repair:

So when I received Matt's new frames, I decided to try out the solid oak 4000 frame on this unit. I removed the aluminum panels, platter and keypad to be able to remove the damaged plinth:

Then I installed the solid oak one that carries the 4000 metal frame. Here are a few impressions of the awesome look of this new plinth:

I absolutely love this fresh and happy oak look! A perfect complement to the bright aluminum plates. In my opinion it looks better than the original teak frame (oh, what heresy!!...;-). Matt really did a wonderful job with this cabinet! I cannot wait to install the Granadillo frame on a needy 4002.

This Beogram 4000 is on its way to a like-new look and performance! I will fully restore it and then it will be available to another B&O enthusiast! Stay tuned!