Beogram 4004 (5526): A New Arrival from New York - First Look

I recently received a Beogram 4004 (Type 5526) from a customer in New York for a full restoration. The unit came safely packaged in a Beolover shipping container (watch the packaging process in the video posted on my 4002/4004 page, it reliably prevents shipping damages). I extracted the unit and put it on the bench:

The hood is quite scratched as if a miniature ice dancer had spun her pirouettes across it..;-):

In absence of new reproduction hoods from the dksoundparts store this hood could be polished back to a decent look, while we wait for them to get their act together (all eyes are on you!...;-). The hood hinges seem in good condition without any discernible cracking. Unfortunately there are a few damages on the inside, which cannot be polished out. But this hood could certainly look more presentable than now after polishing it.

The keypad has the usual use-smudges and also a few scratches:

These smudges come from touching the keys which over time thins and damages the coating. Luckily, we now have a restoration process in place that could make this pad look like new again. Original keypads that still lookg decent can be protected from further decay by installing the Beolover Commander Remote Control for Beogram 4002 and 4004, which allows full control of all functions without needing touching the keys ever again.

The platter is in pretty good condition except one fairly long scratch in the center:

The plinth is also still fairly decent. It only has one small chip on the left corner:

If perfection is desired a beautiful new CNC machined plinth could be installed. They are of much better quality than the original veneer on particle board frames.

The right corner is still pristine:

I removed the aluminum plates and the platters:

The deck looks fairly original under the hood. I found the usual orange fragments from degraded transport lock bushings:

These will be replaced with a Beolover Transport Lock Bushing Set for Beogram 4000, 4002, and 4004.

After this visual inspection I plugged the Beogram in and pressed START. Nothing happened at all. I had a look at the fuses, but both were still o.k.. This suggested an issue with the carriage drive circuit. I manually drove the carriage off the SO ('switch off') switch by turning the carriage pulley a few rotations. After the switch was cleared, the light at the end of the sensor arm came on, indicating that the unit powered up. Pressing the << >> < > buttons yielded no response. Also the platter motor did not rotate. But I was able to raise and lower the arm. So clearly some mayor issues are present in this unit. The platter motor seemed completely seized and I was not able to turn it by hand. A non-standard too-long screw on the motor mounting plate indicated that there some previous interventions already happened:

Overall, I think this unit is a pretty decent candidate for a nice restoration, especially if the cosmetic issues would be alleviated. I am confident that the functional issues can be cured and like-new functionality will be achieved once I am done with my process. Stay tuned!

Beogram 8002: Repair of Intermittent Tracking Issue

Oh well, I guess I declared victory a bit too early on the Beogram 8002 that I recently restored for a customer in California. After celebrating the restored Beogram with an awesome Manfredo Fest record

I continued playing it for a few days. I always like to do this before I send a Beogram back to its owner trying to reduce the likelihood of intermittent issues coming up later.

During this 'play period' of my restoration process I started noticing that there were sometimes irregular distortions during playing records. Sometimes the needle even skipped occasionally on records that I knew are in pretty decent condition and never skipped before. So I had a closer look at what was going on. After watching the carriage mechanism for a while I finally realized that this unit exhibited 'reluctant tracking' similar to what one notices occasionally in the earlier Beogram 400x series of turntables. Their carriage motors develop too much friction internally and that causes tracking 'hiccups' where the carriage only moves in larger jumps after a few turns of the platter. If the carriage mechanism is properly restored and has low friction, this usually indicates that the motor itself needs a higher voltage to overcome the initial "sticktion", to go from standstill into motion. On the 400x this does not cause very noticeable distortions or skipping, presumably due to the larger mass of the arm assembly. 

But in the 8002 with its ultralight arm and tiny cartridge, such jumps apparently can cause serious vibrations in the needle which can be quite audible. In severe cases this even causes the needle to jump into an adjacent groove.

This experience suggests to me that the 800x turntables now also may start developing carriage motor issues as they enter 'middle age'. 

This meant I had to setup this Beogram 8002 again in service position to have a closer look:

I really started liking my new 'Lazy Susan' bench setup. It allows working on fragile setups from all sides without the need to bend wires all the time etc...Amazing that it took me more than 15 years to come up with this approach!...;-). On the scope you can see already a trace measured after I had fixed it. I only took this picture after I was done already.

Let's see what I ended up doing:

First I studied the circuit diagram. I never had the need to work on the carriage driver circuit of a Beogram 8002 so far. This snippet from the diagram in the service manual shows how it all works:

One of the two opamps integrated in IC2 is responsible for driving the push-pull stage (TR1/2) that comprise the H-bridge half that controls the current through the carriage motor OM1 in forward direction that is used for carriage advancement during play of a record. In this condition the current flows from the +15V rail through TR1, R43, OM1 and then to ground via TR4 on the other side of the motor. For this to happen the TR1 and TR4 need to be conductive. TR4 is turned fully on by the other opamp in IC2 (not seen in the picture above), by pulling the base of TR4 to ground.

The control of the current happens via TR1 whose base is controlled by pin 7 of IC2. This opamp is configured as 'non-inverting': Its "-" input is connected to the comparison voltage defined by the R20/R18 voltage divider between +15V and ground which is fed into the "-" input via R22. This voltage (10k/230k*15V=0.65V) is compared with the voltage on the "+" input, which defines the output voltage of the opamp at pin 7: Without a feedback line between output and "-" input this would result in a digital behavior where pin 7 would shoot up close to the 15V rail voltage whenever the "+" voltage is larger than the "-" voltage, and go near 0V whenever "+" would be smaller than "-". This comes from the fact that opamps are usually setup to have an 'infinite' gain. To get a more controlled behavior where the output actually mirrors the "+" input smoothly as a linear amplifier, a feedback line is implemented between the output (pin 7) and the "-" input. This is marked green in the above picture. This feedback connection via R21 forms an additional voltage divider with R18. This allows setting the gain of the amplifier via R21: A smaller R21 reduces the voltage swing on the output of the amplifier caused by a change of the input voltage present on pin 5, while a larger R21 increases the proportional voltage swing at the output.

The rest of the tracking feedback process is straight forward: The movement of the arm as the needle is pulled towards the center of the record is translated into a positive proportional voltage on pin 5. This happens via an aperture bolted to the arm that increases the amount of light on the photoresistor 5R1 coming from 5IL2. More light means less resistance in a photoresistor. 5R1 forms a voltage divider with R27, which scales the approx. 4.4V that apply to the other end of the photoresistor during play of a record into the "+" input of the opamp (via D4). So whenever the arm gets pulled toward the center of the record, the voltage at the "+" input increases a bit. If it is above the voltage at the "-" input, the output of the opamp goes up, this turns on TR1 a bit more, which increases the current in the motor. After surpassing a certain threshold (defined by friction) the motor starts moving and the carriage starts following the needle. Once the carriage moved enough to reduce the light on the photoresistor sufficiently the voltage on the "+" input drops, causing the motor to stop. The result is that the carriage moves in small bursts after the needle until the end of the record has been reached.

In the case of this Beogram 8002, the bursts were much larger than normal, i.e. the carriage only started moving after the needle had been pulled a few platter rotations inward. When the movement occurred it gave the carriage a fairly strong jolt, which then caused the distortion and skipping issues. This can be seen on this oscilloscope trace, which was measured at the output of the opamp (pin 7) during play of a record:

Each of the peaks corresponds to a platter rotation. The peak is essentially caused by the eccentricity of the record, causing the arm arm to dance left and right a bit during the inward motion. This causes the aperture to swing left and right which causes the pin 7 voltage to vary accordingly. The trace basically shows how the arm gets pulled further and further inward, gradually increasing the motor voltage. This goes on until the voltage of a peak is finally high enough to make the motor move against the friction. Then the carriage adjusts its position and the process starts anew.

When everything is in good shape there should be a small carriage movement about once per rotation. So the question at this point was how to restore this ideal situation.

The first step was of course to have a look at the motor. I had a weak hope it would be the same type that was used in the earlier 400x designs. It would have allowed me replacing it with a new Beolover Carriage Motor for Beogram 4000, 4002, and 4004 and be done with it. But to no avail, the Beogram 800x series has a different setup:

The reason is that the system voltage of the Beogram 8002 is different and so a different motor design was used. 

This left trying to find a workaround until there will be a replacement for 800x carriage motors!

I immediately thought of ways to increase the voltage that is proportionally applied to the motor when the aperture moves a certain distance. This suggested an adjustment of the gain of the opamp that drives TR1. So I replaced the feedback resistor R21 with a 300k trimmer:

Then I increased the resistance gradually while watching the oscilloscope during record play. When I was happy with the carriage movement I measured the resistance and found that I had reached a value of 166 Ohm on the trimmer.

The oscilloscope trace at this point looked like this:

No more steps after a few turns of the record. Visually, the carriage spindle moved a little bit after each rotation of the platter as it should be. I replaced the trimmer with a fixed value resistor and then it was time to play a record and listen to it. I am happy to report that there was no more skipping and I also did not notice distortions anymore. So I hope this issue is fixed for now and this Beogram is ready for service again. I will listen to it for a few more days, and it this turns out to be true it will be finally time to send it back to its owner.

Restoration of Beogram 4002 Keypad from Boston

 I received a keypad from a restorer who is working on a Beogram 4002 for a customer in Boston. Its surface had the typical wear from years of use, but the keypad frame was in excellent overall condition; an ideal candidate for our full restoration process. Below is how it looked on arrival:

On this keypad, the 33 rpm and Start buttons showed the heaviest wear (typically the Start and Stop keys). I applied gentle, sustained heat to gradually loosen the original adhesive. DC-series models (551x/552x) use an especially resilient, elastic glue.

After removing all adhesive residue, I refreshed the black paint lines around the keypad’s perimeter, which become worn from fingertip contact.

Below is the new replacement keypad plate.

For the back pieces, as part of this service we provide new nylon backs which have better dimensions and don't pull the keys down.

Below is the final result:

This should make for an excellent start to the next phase of the restoration.

Beogram 4004: Repair of Transport Damage

A Beogram 4004 that I had restored in December of 2023 came back to my bench with some significant mechanical damage. After I removed the aluminum panels I found a strongly bent carriage spindle bearing bracket:

Some fairly brutal force must have whacked the deck on its left side to cause the carriage weight to bend the bearing bracket. This basically created so much friction that the carriage was not able to move again. An examination of the enclosure yielded that there is also some damage on the plinth. It seems it was hit by some object on the left side close to the corner where an indentation can be seen:

More scrutiny yielded that the off-switch had a dislocated return spring, which immediately explained why the deck would not shut down anymore:

I did my best to bend the bearing bracket back into shape and I restored the switch:

This essentially allowed the carriage to move again unobstructed and the deck shut properly down again. At this point the deck would still not track properly, however. I realized that the arms were also out of alignment. I restored their orthogonality and parallelism, and then adjusted the tracking feedback. This made the deck work again properly.

I will now play a few records on this deck to make sure I did not miss anything, and then it should be time to send it back to its owner in the UK.

Beogram 8002: Re-Assembly and a Joyful Test Spin with Manfredo Fest

I recently performed a functional restoration of a Beogram 8002 that I had received from a customer in California. This Beogram was in pretty decent cosmetic condition overall, but had a fairly scratched hood. Luckily, the dksoundparts store has new reproduction hoods that look very identical to the original ones. The only issue is that the original aluminum hood trim needs to be transferred if one wants to retain the original B&O labeling. Dksoundparts only offers a generic trim strip for fear of lawyer letters from B&O's suit wearing set. Luckily Co-Beolover Beomazed figured out how to remove the original trim from an original hood without damaging it! 

So, while I was playing the restored Beogram in 'service position' to see if it had any intermittent issues left to cure, I sent the hood to Beomazed and he transferred the trim. This post discusses how he did it. It is a pretty challenging and tedious procedure (and of course involving the heavy use of a Dremel tool!!...;-).

He did an awesome job! The trim did not suffer at all and the new hood looks absolutely pristine!

So when I received it back I re-assembled the deck with the new hood. Here are a few impressions:

Very beautiful! Time for a test spin with Manfredo Fest! I recently discovered this interesting Brazilian keyboarder and composer. It is difficult to find his original vinyls, so I bought a re-issue of his possibly most known record, "Brazilian Dorian Dreams" which was initially released in 1976 on T&M Productions. The re-issue is from the British label Far Out Recordings (FARO219LP). It sounds pretty god in my opinion and the pressing is of high quality with only few clicks and pops. It is available via Amazon in the US. The title song Brazilian Dorian Dreams was an equally educational and joyful experience to me. It is written in the Dorian scale, which I had never experienced before, I think. It gives the track a remarkable sound, which I seem to enjoy very much. The wonderful voice of the vocalist Roberta Davis is probably not hurting this experience either! Check it out, it is definitely worth it! The album is on Spotify for a quick discovery.

Here are a few shots of this magnificent record playing on this fully restored Beogram 8002:

Very Beolovely! I will now play a few more records and then it should be time to return this nice Beogram 8002 to its owner!

Beomaster 2400 (2902): A New Arrival From Connecticut - First Look and Disassembly

I recently received a Beomaster 2400 (Type 2902) from a customer in Connecticut for a full functional restoration. The unit came well-packaged in a foam-padded box and so there was no shipping damage. I took it out of the box and put it on the bench:

I love the sleek design of these units! Opening the top panel revealed the tone controls and FM presets:

While the unit is in pretty good cosmetic condition it has the usual delaminating veneer issue:

I plugged the unit in and received some life signs. Most bulbs seem to work, but the one indicating the Tape input seems to be out. I unplugged it, since it is a good idea to not run unrestored Beomasters of this vintage too long since there is always the danger of burning out the output transistors if the quiescent current trimmers are oxidized. I prefer replacing all electrolytic capacitors and these trimmers first before I start running a Beomaster.

I started the disassembly process, necessary to get to the circuit boards. First came the back and bottom panels:

Then I removed the top cover, which revealed the tone control and FM preset mechanics:

Next in line was the front panel:

This revealed the bulb housings and the tone control indicator foils:

Then I removed the tone control and FM presets PCB:

And finally I unbolted the main PCB and I put a clamp on the transformer to keep it upright during the main PCB restoration.

Then I disconnected the FM box and then I could pull the main PCB away from the frame for direct access to the components:

Let the fun begin!...;-). Stay tuned for an update on this project!