Beogram 4002 (5523): Some Final Touches - Replacing Plinth and Keypad

After installing the BeoloverRIAA internal preamplifier and the Commander remote control, it was time for some final touches for this Beogram 4002 (5523):

Here is an impression of its damaged plinth:

The replacement plinth I recently came across unfortunately also had some small damages. The corners were slightly banged up. Inspired by the veneer repair I recently carried out on a Beomaster 8000, I set out to do the same to this plinth:

This shows the right corner before:

and after I added a bit of veneer and colored it to match:

not perfect, but definitely much better than before. The left corner had a similar issue on the side:

I did a similar job here:

The original keypad had a big hole in the coating of the start key:

I replaced this keypad with a much better one:

Alright! This beolovely Beogram is now ready for the return trip to its owner!

Beogram 4002 (5523): Installation of Beolover RIAA Preamp and 4002 Commander Remote Control

I recently gave a Beogram 4002 (5523) the usual 'functional restoration' treatment, which concluded with the installation of gold plated RCA plugs. My customer subsequently decided on having my just completed internal BeoloverRIAA preamplifier installed along with the 4002 Commander remote control system that allows the control of all functions with a paired Apple remote.

So this is the first 4002 that is outfitted with both the Commander and the RIAA preamp. A truly 'back to the future' Beogram!

This shows the BeoloverRIAA board before installation:

and assembled with the 3D printed support:

and installed onto the output PCB (#8):

On to the 4002 Commander. This shows the board before installation. It plugs directly into the keypad connector on the main PCB:

This shows it installed:

Here is a view of both boards:

Time to celebrate this upgraded 4002!:

I selected "Sam' Suffy" by Marc Moulin. All his 'Placebo' records (1971-74) were recently reissued by Music on Vinyl on appropriately colored vinyl. Perfect for showcasing this ahead of its time Beogram 4002!

Beogram 4002 RIAA Preamplifier: A New Power Supply Design

This is a follow up to my original post about the RIAA preamplifier that I am currently designing for a Beogram 4002. This will enable this Beogram to play directly into a standard AUX or TAPE input on a modern amplifier. At first I was very happy with my initial prototype design and I enthusiastically redesigned the board for a more orderly and systematic appearance and sent it away for manufacturing. Well, I got the boards and I assembled a preamp. Here is an impression of the nice looking board:

I installed it and gave it some more testing:

And it quickly occurred to me that I should have done some more testing before getting the boards made. In the redesign I had replaced the original 7824 voltage regulator that steps down from the 31V rail of the Beogram with a smaller SOT-89 package to save some board real estate for the other components. Well, it turned out that this was an interesting mistake. The smaller package was not only smaller, but also had a smaller ripple rejection capability, which immediately brought a slight hum and some annoying hiss to my attention. The amp otherwise seemed to perform nicely, but it was noisy. Another shock occurred when I accidentally slowed down the platter with my hand while I was doing measurements: A very loud crackling hum was emitted from the speakers in that moment. Very un-Beolovely! This indicated that the DC motor, which was working a bit harder during the episode caused the 31V rail of the Beogram to cave in a bit, low enough to inject some juicy ripple into the 24V regulator, which it happily forwarded to the rail splitter of the single supply (the Beogram only has a positive rail...) amp design.

After all this it was obvious that this design was not ready for prime time yet: Back to the drawing board. I realized that the power supply of the Beogram is pretty dirty due to the DC motor, which is the main load during operation. The back EMF of the motor causes a lot of disturbance, and that is of course not a great thing for an amplifier that is supposed to reliably amplify <10mV signals. It was now clear to me that the power supply needed a lot more attention. I read up on the subject and I designed a new supply based on the Linear Technology LT3063 low noise LDO. This marvelous little package has a ripple rejection of 85dB, which is about 25dB better than any standard 78xx regulator and 35dB better than the SOT-89 unit I unfortunately had selected. Unfortunately, this lovely performance comes with the need of a few external components. This meant I had to design a small additional board that I could solder to the input header of my prototype board. Here is an impression of the piggyback board:

In this design I first go into the standard 7824 regulator to make 24V and then comes the LT3063 to drop the voltage to about 17V. Serializing regulators gives an additional 3dB of ripple rejection. I replaced the original regulator of my prototype board with this board

And then implanted it into the Beogram. Anxiously I fired up the 4002 and dropped the arm next to the platter to get an impression of the noise floor before playing a record. And the result was amazing. Much less noise than before, practically inaudible. Then I slowed down the platter until it stopped. No transmitted ripple at all. So the LT3063 was doing an admirable job! Time to enjoy one of my most recent additions to my vinyl collection and write this post. I am listening to Miles Davis' "Sorcerer" album (excellent quality "two eye" CBS pressing CS9532). How much better can it get! Now this is Beolovely!

The next step with this project is to do some more characterization of the amp and then redesign the board one more time (hopefully...;-) to get a final version going.

Beogram 4002 (5523): Installation of New Gold Plated RCA Plugs

The final item to exchange in the Beogram 4002 (5523) that I just rebuilt were the old somewhat corroded RCA plugs. This shows the original plugs:

Here is an impression of the new Amphenol gold plated RCA plugs during installation:

I really like the clean design of these plugs. It makes installation easy and results in reliable solder connections. And here the end result:

Now we need to wait a bit until I get the PCBs for my new RIAA phono pre-amp design (here is an impression of the prototype board). This Beogram will be the second unit to receive this new Beolover upgrade.

Beogram 4002 (5523): Replacement of a Wobbly Carriage Pulley with a New Aluminum Unit

After pretty much finishing up the Beogram 4002 (5523) that I am restoring right now I gave it a good playing this afternoon and I quickly realized that the carriage made stressed noises when moving fast such as when returning to the home position after paying a side. This meant that the carriage pulley had issues. And indeed, it turned out that it was cracked like so many of them. It seems the old plastic just cannot hold up to the stress put on it by the setscrew and so it cracks over the years to relieve it. Luckily there is Nick (of Beoworld.com) who provides nicely turned aluminum replacements (I'd be happy to put anyone interested in touch with him). It is amazing what difference it makes if the pulley is centered and runs round.

This shows the old cracked and the new pulley side by side:

And this picture shows the new pulley installed. Pretty, isn't it??:

Now the carriage moves smoothly without excess noises. This is Beolove!

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 (5523): Replacing the Incandescent Light Bulbs of the RPM Trimmer Scales with LEDs

Today I replaced the incandescent light bulbs that illuminate the RPM trimmer adjustment scales in the Beogram 4002 (5523) that I am currently rebuilding. I installed my custom designed SMD LED assemblies. LEDs last much longer than incandescent bulbs, i.e. this is a desired upgrade if long term use of the Beogram is the goal. This shows the latest re-design of the LED boards before installation:

These assemblies are available to other enthusiasts. This video shows how to install the LED boards. The first step is to take out the trimmer panel and remove the light bulbs:

Then the LED PCBs can be implanted:

The boards are designed that the original covers still fit perfectly over them:

Then the panel can be re-installed. These two pictures show the LED boards in action. Note the red scale hands. They show up red since the LED replacements are based on red/green bi-color LEDs whose intensities are calibrated to yield incandescent lookalike light, while containing red photons that can be reflected by the red scale hands.

If single color amber LEDs are used this does not work and the hands show up grayish and only turn red if there is red-containing light present from other sources such as incandescent room lights. 

Beogram 4002 (5523): Rebuilding the Control System and RPM Stability Qualification with the BeoloverRPM Device

After fixing the basics (tracking system and platter motor) in the Beogram 4002 (5523) that I am rebuilding right now it was time to get the electronic control system up to spec. An important part is to replace the electrolytic capacitors, replace the baseline RPM trimmers and the RPM and output relays. I also installed a grounding switch that allows to connect system and signal grounds, which is often helpful if there are ground loop/humming issues.

Here are a few impressions: 

This shows the main PCB before rebuilding:

A detail shot of the RPM relay and trimmer section before restoration:

These were the days when they still made relays in Germany...;-). Anyway, after 40 years even a Siemens relay has corroded contacts, and it is a great idea to replace it with a modern encapsulated Japanese quality relay. Another important upgrade for these turntables is to replace the single turn RPM trimmers with 25x multi turn units. Only such trimmers allow a precise RPM calibration. This shows the new relay and the two 33 and 45 trimmers:

They are implanted in a way that their trimmer screws are accessible from the other side of the PCB, that one can adjust them while the PCB is installed.

This shows the main PCB after rebuilding together with the exchanged parts:

I am always a bit sad when the colorful Ta capacitors are replaced by drab modern black aluminum cans. But it is a good idea to exchange the Ta units with modern Japanese 105C grade components since they can literally go up in smoke if their age related failure mode is a short circuit between their electrodes.

After doing the main PCB it was time to focus on the output board that carries the output relay. this shows the original board. It has the same Siemens relay like on the main PCB:

This shows the board after replacing the relay and putting in a new delay capacitor, and doing the ground switch upgrade:

The last step of the overhaul of the electronic system was to deoxidize the contact tabs in the keyboard switches:

This deck has unadulterated tabs, so I did not have to take them out for straightening. I pulled 2000 grit sand paper through the contact areas to clean them from oxidation. Then I coated the tabs with DeoxIT D100 which I applied using a cardboard strip coated with it.

After this it was time to put everything back together and check the motor RPM and do an adjustment of the baseline RPM settings with my recently developed BeoloverRPM device:

After adjusting the 33 and 45 RPM setting to spec it was time to do a RPM stability test. The BeoloverRPM device allows to log the RPM over many hours in 10 sec steps. It is also sensitive to sudden deviations and registers them at any time they occur via an analysis of the standard deviation of the measurement. Here is a graph of the RPM performance of this unit over about 8 hrs:

This is a pretty good result as far as I can tell. There are some small variations in the 0.05% range, which is about the 'wow and flutter' spec stated in the service manual. There is also a slow superimposed RPM drift of a similar magnitude, which may be temperature related.

Since I currently do not have any way to qualify the measurement error of the BeoloverRPM device other than putting it into my Beogram 8000 with uProcessor controlled RPM, I am thinking that the actual variations are probably a bit smaller than what is shown here since any measurement errors should add to the actual variations since they are independent.

Anyway, after this test, I plugged it into my Beomaster 6000 4-Channel and listened to my latest vinyl acquisition, "Aqualung" by Jethro Tull (Steven Wilson Remix), and thought that this deck sounds pretty lovely! This is Beolove!

Beogram 4002 (5523): Restoring the DC Platter Motor

Today was 'Motor Day' for the Beogram 4002 (5523) that I am rebuilding right now. The initial evaluation of this unit indicated the need for a rebuild due to the fairly loud running noise of the motor. It seems that most DC 4002s need some attention in this department these days. The sleeve bearings in the DC motor are usually dry due to aging lubricants, and so one needs to take the motor apart, clean it and re-lubricate the bearings. So I took the motor out and took it apart:

This photo shows the upper sleeve bearing after taking the rotor out:

and this one the lower bearing together with the feedback coils and the brushes:

This one shows me lubricating the upper end of the shaft:

and this one while cleaning the commutator with a fiberglass brush:

After putting the motor back together a test revealed that it ran much more quietly again. On to rebuilding the electronic system.