Beogram 4002 (5524): Full Functional Restoration, Repair of a Broken Out Transformer Mount and Installation of Upgrades

This post describes the restoration work done on a Beogram 4002 (Type 5524, with voltage selector) that I recently received from a customer in South Korea. It also describes the repair of a damaged transformer housing and the installation of the Beolover SyncDrive and internal RIAA pre-amplifier upgrades. My initial assessment of this unit is posted here.

This shows the unit with the aluminum panels and platter removed:

It is in pretty good condition, and luckily I was able to remove the very persistent tape residue from all affected parts with some Goo Gone (a very useful chemical: It did not damage the wood plinth nor any other affected surface). 

As usual, I first focused on the DC platter motor. The oil infusion of the bearings can take up to 3 days and so it is a good idea to get the bearings out at the start of a project. This shows the motor removed from the enclosure:

I took it apart to get to the bearings:

The bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum. Immediately, strong bubbling started, indicative of air leaving the empty pores of the bearing:

While the air moves out, the oil moves in. While this process was underway I focused on the rest of the restoration. First I removed all moving parts from the carriage transport and arm lowering mechanisms for cleaning and re-lubricating. This shows the original condition of the carriage:

Here a picture after removing all the parts. It is a good idea to place the carriage on a soft pad to protect the delicate wiring that is on the underside of it:

This shows the lubricant encrusted components ready for the ultrasonic cleaner:

And after about 1 hr in the cleaner:

Nice and shiny! Beolovely! Then I put everything back together. First I installed a new damper gasket in the damper:

This is important since the original gaskets are usually hardened and deformed. This can result in unhappy surprises during arm lowering, when the needle can occasionally drop hard on the platter without any damping when the old gasket allows air to bypass it.

This shows the carriage back together:

Next came the replacement of the incandescent light bulb in the tracking sensor with a LED setup. This shows the original bulb housing (black) still in place:

I removed it, which revealed the tracking aperture:

This aperture regulates the light exposure to the photo sensor mounted below the aperture. Whenever the light on the sensor becomes too strong due to lateral arm deflection the carriage motor moves the carriage until the light on the sensor is reduced again.

This shows the original bulb housing together with the Beolover Tracking Sensor LED Light Source:

The SMD LED is in the same location as the bulb filament, ensuring proper functioning. The LED assembly is a direct plug and play replacement for the original bulb housing:

Then I replaced the wobbly original plastic carriage pulley with a new Beolover Aluminum Carriage Pulley for Beogram 4002 and 4004:

The final step of the carriage restoration was the cleaning and re-lubricating of the pivot point of the damper to arm linkage. This linkage is in-between the tone- and sensor arm assemblies. you can see it stick out here from the V-cut in the metal piece that is bolted to the back of the tone arm assembly:

The removal of this linkage requires taking out the sensor arm assembly. This shows it laying on its side with the linkage removed:

Of course the small copper plate that helps the arm move laterally when up also was loose. I epoxied it back into place.

After putting everything back together I focused on rebuilding the circuit boards. The two power Darlingtons mounted to the solder side of the main PCB are best replaced with the PCB still installed. This makes it much easier to position them properly when soldering in the replacements. This shows one of the transistors, 1IC1 which regulates the 21V rail. It is usually a TIP120, but in this case it was a TIP122:

The TIP122 is a higher voltage version of the TIP120, but both have the same current capability. For this particular application the 122 does not represent an advantage since the voltage is significantly below the 60V the TIP120 is rated for. I usually replace these transistors with their higher current versions, the TIP102 for the TIP120 and the TIP107 for the TIP125 (1IC4). This shows the new 102 in place:

for some reason these new TIP packages need a 100nF capacitor fitted to their emitters in order to quench a strange high frequency modulation that can upset the record detection circuit. 

After replacing the two Darlingtons, I removed the board so I could get to the component side. This shows the board in its original condition:

A detail shot of the RPM control section with the National type RPM relay and the two master trimmers to the left for RPM calibration:

I replaced all electrolytic capacitors, power transistors, RPM relay, and the sensor high-gain transistor that is often out of spec with too little gain left, as well as its biasing resistor with a trimmer. I also replaced the RPM trimmers with modern 25-turn units for a more precise adjustment:

This shows a close up of the rebuilt RPM section with the new Beolover National style RPM relay assembly in place:

Then I removed the keypad assembly to get to the output board that is bolted in underneath it:

This board has the muting circuitry on it as well as the output socket:

I replaced the Siemens style relay with the appropriate Beolover replacement part. I also replaced the 100uF capacitor that helps defining the time constant of the relay action and I installed a switch (red) that allows connecting system and signal grounds in case there is a hum:

At this point I usually remove the floating chassis to replace the transport lock bushings and to vacuum out the enclosure from any fragments of the degraded original bushings. When I started disassembling the transport locks, however, I realized that the plastic transformer housing had broken out mounting tabs:

This may have happened during the event that led to the cracked hood during shipping. Transformers are pretty heavy and therefore prone to such damage. Especially when the housing is plastic. This transformer just sat loosely attached by its wiring and I was able to lift it up:

I sat down and designed a part that would allow me bolting it in when I would put everything back together. While the first prototype was printing, I focused on cleaning out the enclosure. I removed the original reservoir capacitor of the 21V rail:

and then the floating chassis and the plinth. This left me with an empty enclosure. I vacuumed out the transport lock fragments and other dirt:

This was a good moment to remove the remaining tape residue from the bottom of the enclosure:

I drenched this stuff with Goo Gone and after 30 min soaking time I was able to wipe off the residue with a paper towel. Then I cleaned off the Goo Gone with hand dishwashing detergent and the enclosure bottom looked decent again:

Then I installed new Beolover transport lock bushings. They come in two halves for easy installation:

Simply push in one half from the bottom

and the other from the top:

Et voila!:

After putting the locks back together I installed a new Beolover reservoir capacitor assembly:

This Beogram 4002 was setup with a single power rail, i.e. all I needed to do was to solder the white and black wires from the power entry plug of the main board to the respectively labeled solder pads on the assembly. The other solder pads could be ignored. They are used in dual power rail Beograms.

After this installation, I focused on replacing the remaining three incandescent bulbs. First came the two in the RPM panel above the keypad. They illuminate the RPM adjustment scales. This shows the RPM panel removed and flipped over. This revealed the two bulb covers:

I pried the covers off and the bulbs became apparent as shown here:

The two small green boards in front of the RPM panel are the Beolover RPM Panel LED Backlights for Beogram 4002 and 4004. They solder directly to the solder pads where the bulb wires were connected:

This shows one of them magnified:

The boards essentially function as extensions of the board that supplies the bulbs with power.

The final bulb to be replaced was in the sensor arm compartment. This shows the compartment pulled out with the Beolover Sensor Arm LED Light Source for Beogram 4000, 4002 and 4004:

I installed the Beolover part:

Then it was time to test the LEDs. This shows the 33 RPM LED in the RPM panel in action:

It emits a nice incandescent-like glow. And here an impression of the B&O logo lit up by the sensor arm LED:

Then it was time to adjust the sensor arm bias voltage:

The spec is to get 4V at the collector of 1TR3. After setting the bias voltage and moving the adjusted trimmer to the component side of the board, it was time to check the sensor action. I connected my oscilloscope to the collector of TR3 and spun the platter by hand. This is the signal I received:

Each dip of the voltage corresponds to a black platter rib passing underneath the sensor. If the amplitude exceeds 5V the spec is met. In this case I saw about 5.5V, so all good in the sensor department!

After a few design iterations of the transformer part I achieved a good fit to the shape of the transformer housing. This is an impression of the new part:

It fits snugly around the transformer housing:

With two longer screws it bolted nicely to the original mounting holes, clamping the transformer safely to the enclosure bottom: 

Now it was time to do the chassis and platter adjustments. This somewhat tedious process makes sure that the platter is parallel to the arm movement and in the correct distance, and that the platter is centered and flush with the surrounding aluminum panel. In many beograms this can take some time to achieve due to the significant 'adjustment space'. This process often requires several iterations until a satisfactory adjustment has been achieved.

Once this was in place, the tonearm adjustments could be made. First I replaced the flimsy locking washer on the arm counterweight adjustment screw

With a M3 nut and a washer:

This allows locking the tracking weight calibration in place for shipping. After this was done I adjusted the arm lowering limit:

This is an important adjustment since it prevents catastrophic stylus damage in case the record detection circuitry fails and the arm gets inadvertently lowered on an empty platter.

The next step was calibrating the tracking weight. Since the little adjustment dial on the arms assembly is notoriously inaccurate across its entire scale, I usually adjust it for accuracy around the 1.2g point since this is the tracking weight that B&O cartridges need:

In general, I recommend that the weight is occasionally checked with a digital gauge and the dial simply adjusted for proper weight regardless of the scale reading.

In the meantime the oil infusion process had come to a conclusion as was evident from the absence of air bubbles coming from the bearings. I broke the vacuum and extracted them from the jar:

I put the motor back together with the freshly infused bearings. Then it was time for a 24 hrs longterm RPM stability measurement with the BeoloverRPM Device. In its 'slow' mode, it allows logging the RPM in 10s intervals for extended periods of time.

This is the curve that I had measured after about 24 hrs:

This is pretty much as good as it gets with DC platter motors. With these motors there is always some long-term drift, usually caused by thermal effects, especially now in summer when I need to run the AC in my workshop during the day. Such drift is a normal characteristic of analog control systems. Overall, this change is happening pretty slowly, and it is on a magnitude that is impossible for humans to discern. This motor is ready for duty again! 

Next, I ran the BeoloverRPM in its 'fast' mode to get a reading on 'wow and flutter', i.e. RPM changes on a short time scale:

In the fast mode a RPM measurement is recorded each time a platter rib passes under the sensor. This generates high-resolution RPM data that looks like this:

This graph covers about 60 platter rotations, or about 120 sec. of runtime. The interesting pattern is a convolution of real RPM changes and a measurement artifact that is a result of the very slightly irregular spacing of the platter ribs around the platter. On closer inspection, the zig-zag pattern is repeated every 24 measurement points (there are 24 ribs...) and can be regarded as a 'fingerprint' of a particular platter. It turns out that each Beogram platter has a distinct pattern due to manufacturing tolerances when the slots were machined for the black rubber ribs.

The overlaid sine-wavy pattern, however, reflects real RPM changes that are introduced by the feedback based control system that keeps the motor RPM constant. An evaluation of this wave pattern yields a wow and flutter percentage of about 0.1%. The service manual lists 0.05% as the spec for the DC platter motors, but this 2x difference may well be related to the different way this was measured in the 1970s in absence of modern microcontrollers. At any rate this difference is pretty academic since it is much to small to be discernible. This original DC is back in business!

Nonetheless, my customer decided to upgrade his Beogram with the Beolover SyncDrive and trade in his original motor. The SyncDrive assembly is a drop-in replacement for the original motor and it directly bolts to the motor mounting posts. The SyncDrive improves wow and flutter of any DC motor Beogram to the lower level of the earlier AC-motor Beograms, while ensuring a RPM long-term stability similar to the later Beogram 8000/8002 models. Due to its digital control system it is less affected by thermal drift etc...This is how it looks when installed:

My customer also wanted the Beolover RIAA internal phono pre-amplifier installed. It is also a plug-and-play upgrade that simply replaces the original output board. Here you can see the original board installed and the RIAA board next to it:

And here after the swap:

Before finally giving this restored Beogram 4002 a first spin there were two more items to be addressed: One was the replacement of the original grimy and slightly oval DIN5 plug

with a nice new all metal plug with gold plated contact pins:

And then there were the usual cracked RPM panel holders. They often break when the RPM panel is not properly removed and the pins are forced out at an angle. This Beogram had damaged holders on both sides:

Luckily, the Beoparts-shop in Denmark has nice replacement parts that directly replace the originals. Here you can see the new ones next to the darker original ones:

All that needs to be done is to move the original metal springs over to the new plastic parts:

And then it was finally time for a first spin! I selected the lovely Herbie Hancock album "Thrust!" from 1974. Jazz-Funk at its finest and a perfect contemporary complement for this lovely Beogram 4002!

My favorite track is "Butterfly" on Side 2. Smooth but with a nice melody and a funky rhythm. Perfect for spending time at the bench restoring Beograms!...;-). Of course this nice original pressing was ultrasonically restored to perfection with a CleanerVinyl ProXL setup!

Here an impression of the Beogram and Herbie in action together:

I will now play this deck for 1-2 weeks and if nothing intermittent comes up it will be time to send this Beogram back to South Korea!

While I was testing this deck, I still had to come up with a replacement for the damaged hood:

Unfortunately, many original hoods have hinge areas that are developing cracks. The reason is that they used flat head (countersunk) screws to bolt the plexiglass to the metal hinge. The 45 degree cone shape of last heads causes outward stress that over time cracks the plexiglass around the bolt holes. The hood that I had available also had started developing such cracks on both sides:

Luckily, I still have a few of my hinge patches and installation clamps:

I had homed to never have to use them again since newly reproduced hoods became available at the Beoparts-shop. Sadly, they are out of stock already for more than six months and it seems it may take another half year until they may come back. So in the meantime I am back to restoring hoods!

I glued the patches to the cracked areas and pressed them in with the clamps:

After letting the glue harden for 24 hrs I removed the clamps and drilled out the counter sunk holes to remove the squirted out glue remnants:

This hood also needed new rubber bumpers. As usual the original ones were completely degraded. I usually drill them out with a 2mm drill bit:

And then I install a 2mm thick O-ring snippet and cut it to 1mm length. This works very well:

Here an impression of the repaired hood:

Not perfect, but it will tide my customer over until the Beoparts-shop gets its act together and new hoods hopefully will become available again!