Beogram 4004 (5526): Full Functional Restoration and Installation of a Beolover RIAA Pre-Amplifier Board

This post discusses the functional restoration of a Beogram 4004 (Type 5526) which I had received from a customer in Georgia. The post also shows how to install a Beolover RIAA pre-amplifier board, which directly replaces the output boards of Beogram 4002 and 4004. My initial assessment of the unit is discussed in this post.

This shows the unit as received with the aluminum panels removed:

As usual, I started with the DC platter motor and extracted it for disassembly to extract the bearings, which, as usual, were in need of an oil infusion:

This shows the dissembled motor. The two bearings are up front on the black pad:

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

The bubbling represents air being drawn from the pores of the Oilite bearing material. As the air exits oil diffuses into the material, replenishing the oil loss that occurs during running the motor. This process usually takes 2-3 days. While it was in progress I focused on the other restoration tasks, starting with the carriage:

I removed all relevant moving parts for cleaning in an ultrasonic bath:

This shows the extracted lubricant encrusted parts:

And here a picture after completing the cleaning process:

Beolovely! It is important to replace the damper gasket with a new one:

This ensures a consistent arm lowering experience. Then I put the carriage mechanisms back together:

There is one more linkage that needs to be extracted, cleaned and lubricated: The damper-to-arm linkage. You can see it here sticking out the back of the arms assembly, sitting in the V-cutout of the linkage that connects it to the back of the tonearm assembly:

To get to the linkage the sensor arm needs to be removed:

After taking the circlip off the linkage can be removed and the pivot point cleaned and re-lubricated:

After re-assembly the arm needs to be bolted back in and its alignment with the tonearm and the carriage rods reestablished:

There are two more items to be addressed on the carriage: The tracking sensor bulb needs to be replaced with a LED assembly, and the plastic carriage pulley needs to be replaced with a machined aluminum replica. This shows the original black tracking sensor bulb housing still installed: 

I removed it. This shows the bulb housing together with the Beolover LED replacement:

And here it is installed. It is drop-in and directly replaces the bulb without any further modification:

The small blue 'box' on top is a trimmer that allows adjusting the intensity of the LED. This is helpful for fine-tuning the tracking feedback.

This picture shows the new precision machined aluminum pulley for the carriage drive:

On to replacing two more incandescent light bulbs: This shows the RPM adjustment panel extracted and flipped over:

After removing the bulb covers:

With Belover LED assemblies installed:

They directly replace the light bulbs and are soldered to the solder points of the bulbs.

They do not interfere with the bulb covers, which can be put back into place after the LED installation:

The final bulb that needs replacing is in the sensor arm. This shows the original setup with the small bulb in its compartment. Next to it is the Beolover LED assembly that replaces the bulb, together with its alignment guide:

This shows the board installed:

And in action:

The use of a warm white LED ensures emission of enough red photons to correctly illuminate the B&O logo at the end of the arm.

The next step was rebuilding the circuit boards. It is best to replace the two power Darlingtons that are on the solder side of the board first, while the board is still bolted in. This ensures proper alignment of the replacement devices. As example this shows IC1, a TIP120, that serves as the voltage regulator of the 21V power rail:

I replaced it with a contemporary TIP120 and put a 100nF capacitor across the output:

The capacitor is necessary since modern TIP120 for some reason introduce a high frequency ripple on the output, which can disable the record detection function.

After replacing the two Darlingtons, I removed the board. This shows the component side in original condition:

I replaced all electrolytic capacitors, all power transistors, the RPM trimmers, the RPM relay, and the sensor arm amplifier:

On to the output board:

On this board I usually replace the output relay and the capacitor that defines the time constant of the relay delay after arm lowering is activated. In 4004s there are three more electrolytic capacitors in the remote control circuitry that allows controlling the deck via the remote of a Beomaster 2400. This shows the rebuilt board:

With the boards and the keypad removed, it is a good moment to tend to the transport locks, which had the usual degraded rubber bushings:

This deck also had very bent tabs on the plinth. With everything removed from the enclosure it is a perfect moment to also take off the plinth and straighten such bent tabs:

This shows the empty enclosure, which was vacuumed to remove all the debris from the transport lock bushings:

This is important since the fragments can hinder the floating chassis from floating due to the limited space between chassis and enclosure bottom.

This shows the 3D printed replacement bushing parts:

Each bushing is replaced by two parts: One inserts from the bottom, the other from the top for easy installation:

After re-installing the locks, I replaced the original reservoir capacitor:

Before the putting in the keypad I had to replace the cracked assemblies that hold the RPM panel in place. This shows the original left/right assemblies:

Luckily, there are now identical replicas available from the Beoparts store in Denmark. Dillen of Beoworld designed and put them into production. Very awesome! Thank you!:

All one has to do is poking the little springs out of the original cracked parts and transfer them to the new ones, as shown here:

This shows one of them installed. Beolovely!:

Time for testing the record detection circuit. This shows the adjustment of the bias of the sensor transistor to yield 4V at the collector:

After that I put on the platter and spun it under the sensor, while measuring the collector signal with my oscilloscope:

An amplitude equal or larger than 6V guarantees a reliable record detection function. I measured a nice 7V, i.e. everything is perfect in this department!

The next step was making all the platter and chassis adjustments. The goal is to get the platter parallel to the arm motion, the proper arm to platter height, as well as a flush platter relative to the aluminum plates. This can be a bit of a fussy task that can take some serious time to get right. Often only repeat iterative adjustments can yield a perfect alignment of all the parts.

After this is done, the arm adjustments are next. When it comes to the tracking weight calibration, I usually replace the flimsy circlip at the counter weight adjustment screw

with a M3 nut that allows locking the calibration in place once the proper weight has been set:

Due to my recent move to Albuquerque, my digital tracking weight gauge was AWOL, and so I resorted to  an original B&O weight balance that came with the Beograms when they were bought new:

They are pretty easy to use: all one needs to achieve is to get it balanced level with the needle at the correct spot of the weight scale that is printed on the balance:

I checked my 'analog' adjustment the next day after having received a replacement from Amazon:

Pretty good! So there is really not much of a reason to go with a digital gauge, except for convenience purposes.

After the weight had been calibrated, I adjusted the arm lowering limit that the needle misses the lower parts of the platter ribs by about 1 mm:

This is an important adjustment as safeguard, should the record detection mechanism ever fail due to a circuit malfunction.

The final adjustment was the tracking feedback:

The carriage motor should start moving after about 2 turns of the platter after the arm has been lowered.

At this point the bubbling around the platter motor bearings had stopped, and I extracted the bearings from the oil:

Then I re-assembled the motor and bolted it into the Beogram. Then I performed a 24 hrs RPM stability test with the BeoloverRPM device:

The BeloverRPM allows logging the RPM in 10s intervals, perfect for spotting intermittent RPM variations. This is the curve I measured after 24 hrs:

This curve is pretty much as good as it gets with Beogram DC platter motors. The slow drift over the hours is related to thermal changes and the small peaks are related to the new bearing orientation relative to the shaft, which will go away over time as the shaft polishes the bearing.

This Beogram restoration was coming close to the end, and so it was time to replace the original corroded DIN7 

with a new DIN5 with gold plated pins (DIN5 was chosen since my customer will not use this 4004 together with a Beomaster 2400, which uses the two additional pins for the remote control functions):

My customer decided to have the Beolover RIAA pre-amplifier installed since the deck will be used with an amplifier without Phono input. This shows the RIAA board:

It directly replaces the original output board in a plug-and-play fashion. This shows the original board with the keypad and RPM panel flipped over:

Installation is very straight forward: Just unplug the three plugs that connect to the board,

take the board out,

and plug the Beolover RIAA board in:

Once that is done, drive the carriage a bit away to the left, then bolt the grounding wire from the RIAA board to the post that holds the small plexiglass alignment fixture for the board:

Now the keypad can be bolted in again:

And that is all there is to install the Beolover RIAA board!

Now it was finally time to give this fully restored Beogram 4004 a test spin. I selected one of my favorite Dexter Gordon records, "A Swingin' Affair" that he recorded in 1962. I only have a German re-issue from the 70s when I started buying records, but is still sounds great, especially after having been restored to its original glory by ultrasonic cleaning with a CleanerVinyl ProXL setup.

A perfect album for testing this lovely Beogram 4004! Both look great together: 

I will now play this Beogram 4004 for a couple more weeks to make sure it has no intermittent issues. During that time I will also install a new reproduction hood to replace the original one, which unfortunately has cracked around the hinges. Stay tuned!