Beogram 4004 (5526): Full Functional Restoration, Installation of the New Beo4 Enabled Commander Remote and a Test Spin with Mr.T.!

This post summarizes the work done during the full functional restoration of a Beogram 4004 (Type 5526), which I recently received from a customer in California. This post discusses my initial assessment of the unit.

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

As usual, I started with the DC platter motor. They all seem to need their dry bearings vacuum infused with fresh oil. Otherwise they produce significant RPM variations that can ruin any listening experience. This shows the removed motor:

I took it apart to get to the bearings. They are the small donuts on the black pad up front:

I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

The bubbling is indicative of air being drawn from the porous Oilite bearing material to make room for oil diffusion into the material. This process usually takes about 48-72 hrs.

In the meantime I focuses on the other restoration tasks. I began with the mechanical systems on the carriage, the arm lowering and the carriage transport assemblies. This shows the original setup:

I removed all moving parts and secured the carriage on a foam pad to protect the filigrane wires at its bottom side:

This shows the extracted parts ready for the ultrasonic cleaner:

While the carriage was separated from the floating chassis it was the perfect moment to check the cartridge connections (when I received this deck the tonearm was loose, suggesting there may be an issue with the connections that someone had a look into). I measured the continuity for all 4 cartridge connector traces (note: for this measurement the plug needs to be pulled from the output board) from the MMC tab to the connection terminal on the bottom side of the carriage. And indeed one of the traces was not connected through:

I pulled the arm off its base and had a look, and indeed there were only three wires connected (excluding the system ground wire). The green wire was awol:

Luckily, it was just pushed a bit into the arm tube

and I was able to pull it out with narrow tweezers. I soldered the wire to its terminal on the base:

It was probably ripped off when the arm was pushed back onto the base during a repair attempt. This easily happens if one is not careful since the wires can hang out below and then when the base is pushed in they can get caught and rip off.

Anyway, this was fixed and so I moved on to replacing the incandescent light bulb in the tracking sensor. This shows the original black tracking sensor bulb housing in place:

I removed it, which revealed the tracking feedback aperture:

Depending on the lateral arm deflection, it exposes a photo resistor in the lower part of the housing to more or less light, which is the control signal for the carriage advancement. This shows the original bulb and the Beolover Tracking Sensor LED Light Source in direct comparison:

The LED sits in the same location as the filament of the light bulb. This shows the part installed:

In the meantime the parts came out of the ultrasonic sparkly clean:

When I assembled the damper, I installed a new damper gasket:

The original black gaskets are usually hardened, which can result in inconsistent arm lowering speeds. So it is a good idea to replace this gasket whenever the damper is disassembled.

This shows the cleaned parts re-installed:

Beoshiny! I also put on a new precision machined aluminum pulley replica to replace the original cracked plastic one:

The final step on the carriage assembly was cleaning and re-lubricating the pivot point of the damper to arm linkage. It is mounted on the sensor arm assembly:

The linkage sticks out from the small V-cut in the metal piece bolted to the back of the counter weight. The sensor arm assembly has to be taken out for this procedure:

Thispicture shows the linkage removed:

I cleaned the small shaft on which it moves and re-installed the linkage:

As usual, the small copper plate that helps the arm move laterally in its up position came loose with a slight tweezer tug:

I removed the degraded double sided tape residue and glued it back in place with a dab of epoxy:

After re-aligning the sensor arm assembly it was time to restore the circuit boards. I usually begin with the main board. It has two power Darlingtons installed on its solder side. It is best to replace these transistors first with the board still installed. This simplifies aligning the replacements correctly that they line up with their mounting holes. This shows TR1, the TIP120 Darlington that regulates the 24V power rail:

I replaced it with a stronger TIP102 and also installed a (yellowish) 100nF capacitor between its emitter and ground. This capacitor quenches some strange high frequency oscillations that modern Darlingtons produce in this circuit configuration:

After also replacing TR4, the Darlington that controls the current through the solenoid, it was time to remove the board and focus on the component side. This shows the board in its original condition:

And after replacing all electrolytic capacitors, power transistor and the RPM replay and trimmers:

This show the rebuilt RPM section in detail with the new Beolover RPM relay (National style):

Next came the output board. This shows it in its original condition:

This board is the essential difference between Beogram 4004 and 4002. The 4004 version contains additional circuitry (on the left) that allows rudimentary control of the deck via the remote control of a Beomaster 2400. The actual output relay section is identical to what is usually found in 4002s:

I replaced all electrolytic capacitors and the output relay:

I also installed a (red) switch that conveniently allows connecting signal and system grounds in case there is a hum:

Then I focused on replacing the incandescent bulbs in the RPM panel above the keypad. This shows the panel removed and flipped over:

I removed the bulbs and prepared the assembly for the Beolover RPM Panel LED Backlights. They are the two small green/orange components in front the the panel:

The removed bulbs are below the LEDs. I installed the LED boards:

This shows one of them in more detail. They solder directly to the pads where the bulbs are connected, sort of an extension of the small PCB that makes the connections for the RPM panel:

The bulb covers can be reinstalled. There is no interference between the LED panels and the covers:

The final LED needing replacement is in the Sensor arm. This shows the small sensor compartment pulled out from the end of the arm. The original bulb is still in place and the Beolover Sensor Arm LED Light Source with its alignment piece is next to it on the right:

This shows the LED board implemented:

At this point pretty much everything was removed from the enclosure except the floating chassis. The next step was also removing their chassis to replace the completely degraded transport lock bushings. This shows one of them:

And hear the left-behind debris after taking out the floating chassis. A nice mess!:

I also removed the big reservoir capacitor that stabilizes the 21V rail:

And with that the enclosure was empty:

If you look closely you can see all the bushing fragments strewn around. Their removal is crucial during a restoration since they can impede the floating motion of the chassis and that reduces its capability to protect the turntable from vibrations. I vacuumed everything out:

Then it was time to install a new Beolover Transport Lock Bushing Set. These replacements are designed for easy installation. They each come in two identical halves that can installed by simply pushing one half in from the top and one from the bottom:

This is shown here:

Here one of the restored bushings is shown during the installation of the floating chassis:

And a photo of the completed lock:

Another advantage of the Beolover bushings is that they are a little thinner than the originals. This gives more leeway for adjusting the floating chassis properly.

With the chassis in place, it was time to install a new Beolover reservoir capacitor assembly. It comes with a red alignment piece that securely holds the circuit board with the capacitors in place:

Since this beogram had one of the later single capacitance type reservoir capacitors only two connections needed to be made, the white and black wires from the original capacitor need to be soldered to the respectively labeled solder pads on the PCB. With that done, the board can be bolted in with the screw that held the original capacitor in place:

Before I put the keypad back in, I replaced the cracked RPM panel holder on the right

with a new one from the Beoparts-shop in Denmark:

These parts are nice reproductions. All that needs to be done is move the metal spring parts over from the old cracked one.

After installing the keypad and the PCBs, I adjusted the bias of the new sensor arm transistor to yield the prescribed 4V at the collector:

After this adjustment I adjusted the platter height relative to the arms and made sure that the platter was also parallel to the arm travel. Then I adjusted the floating chassis in a way to get the platter flush with the aluminum panels. After this iterative and time consuming process, I focused on the remaining adjustments:

First I calibrated the tracking weight. Before I did the calibration I replaced the flimsy locking washer that holds the counterweight adjustment screw in place with a square M3 nut. This allows locking the calibration in place so it survives the rigors of shipping:

Then I adjusted the counterweight that the small weight dial was approximately accurate around 1.2g, which is the typical weight B&O cartridges demand:

The next step was adjusting the arm lowering limit to prevent desaster should the needle ever be lowered on a spinning empty platter due to a sensor malfunction:

Then I adjusted the tracking feedback.

My customer decided to get the original convertible DIN7 plug 

replaced with a modern gold plated DIN5:

DIN7 is only really needed if a Beogram 4004 is to be used with a Beomaster 2400. The two additional pins carry the remote signals to start/stop the deck via the Beomaster remote control.

All that was left to be done before a first test spin was putting the platter motor back together. The bubbling in the oil jar had stopped at this point and so it was time to extract the freshly re-infused bearings:

I installed them back in the motor enclosure:

And then I put the motor back together and installed in the Beogram for a 24 hrs RPM stability test with the BeoloverRPM device. This shows the BeoloverRPM installed on the rim of the enclosure performing a measurement in its 'slow' mode:

The 'slow' mode is perfect for precisely tuning the RPM and for longterm RPM stability measurements. It sends a RPM measurement every 10 sec to the serial port of the computer it is hooked up to. This is the curve I had measured after 24 hrs:

This is a pretty good result for a freshly restored Beogram DC platter motor. There is some longterm drift that is most likely related to temperature changes, and there are a couple small peaks that relate to the replenished bearing settling in place. The shaft needs to polish it in its new orientation. It can be expected that the RPM will still get a bit more stable after playing the deck for a few dozen hours. The 'noise' visible in this graph is a measurement artifact that comes from slight variations of the rib spacing around the platter. The BeoloverRPM essentially measures the time between ribs passing under its sensor.

This phenomenon can be more closely observed in the 'fast' mode of the BeoloverRPM, which plots an RPM value every time a rib passes under the sensor. The picture below shows the device in action and you can see a periodically repeating pattern on its screen:

This graph shows this measurement for about 60 platter rotations, i.e. the graph has about 60x24 measurement points (there are 24 ribs on a platter):

Each 'peak' corresponds to a platter turn. The repeating 'fine structure' of the peaks is essentially a fingerprint of this particular platter. In my experience it looks different for each Beogram. The superimposed sinusoidal looking curve shape is essentially a wow and flutter measurement. It shows the variation of the platter speed caused by the feedback based motor control system. The platter motor essentially feeds its speed back into the motor circuit, and whenever the speed is too high, the circuit regulates it down until it is too low, and then it gets faster again until the process repeats. This yields small periodic RPM variations that can be seen in this graph. Evaluation of the wavy part suggests that the wow and flutter variations are about 0.1%, which is about 2x than what the manual states (0.05%). This may be a real discrepancy, but it could as well be systematic since back in the 70s no digital RPM measurements were possible and this was done by measuring variations of a test tone on a test record. At any rate these fluctuations are way too small for humans to discern, and so we can conclude that this motor is back in business and can be used for listening to records!

And with this it was time for a test spin of this restored Beogram 4004!

I selected one of my favorite CTI records, "Don't mess with Mister T." (CTI 6030). The T of course stands for Stanley Turrentine! He recorded this album in 1973, a perfect contemporary for this lovely restored Beogram 4004! And what an awesome cover picture this album has. You definitely don't want to mess with Mr. T!...;-). Of course this lovely record was cleaned ultrasonically using a CleanerVinyl ProXL setup to restore its sound to its original glory. Here an impression of this great moment when everything came together:

After this test it was time to install the new Beo4 enabled Commander remote control:

The installation is exactly the same process, like for the standard Commander that uses an Apple remote. 

More info about the Beo4 Commander can be found here.

I will now play this deck for a while and if nothing new comes up, this Beogram will be ready to return to its owner!