Beogram 4002 (5503): Installation of Upgrades - Internal RIAA Preamp, Commander Remote Control and a New Hood

After completing the functional restoration of a Beogram 4002 (Type 5503) that I had received from Oklahoma, it was time to install the upgrades my customer desired. He wanted the internal Beolover RIAA pre-amplifier that I recently updated to fit AC motor Beogram 4002s, the Beolover Commander remote control system and a brand new hood to give this Beogram a pristine like-new look.

I started out by preparing the keypad for the Commander remote system. This shows the complete Commander kit for AC motor Beogram 4002s:

The small narrow circuit board to the right in the above picture is the keypad adapter. Since AC motor Beograms still mostly rely on directly soldered wiring harnesses, the installation of the Commander is unfortunately not 'plug and play' like the DC motor version. Instead, a breakout for the keypad signals needs to be created that the Commander can communicate with the control system of the Beogram and take over the keypad functions. 

This shows the keypad PCB after pulling it out from its slot under the keypad:

The solder pads on the left side connect to the wiring harness that sends the keypad signals to the main board. This shows the contact pads magnified:

The keypad breakout fits onto these pads, but a 'corridor' needs to be generated by removing some of the solder that the adapter can be soldered in. This is shown here:

When I took the above picture I already had added some solder flux to the pads in preparation for soldering the adapter in. This shows the adapter (also with some flux on the pads):

The adapter essentially connects the small white connector 1:1 to the keypad pads. When soldering it in, it is best to first tack it on only on two of the terminals so the fit can still be corrected easily. This is shown here:

It is important to make sure the board sits orthogonally respective to the keypad board:

Once the orientation is satisfying the remaining pads can be soldered into place:

Before I continued with the Commander installation I plugged the Beolover RIAA preamp board in since this needs to be done while the keypad is removed. This shows the original output board still in place together with the new green RIAA board on the right:

Implantation is a straight forward board switch. The RIAA board has the same connectors as the original board. This shows the board installed:

Then it was time to slide the modified keypad board back into its slot under the keypad:

Then I bolted the Commander board in (it uses one of the main PCB bolt holes):

After this I plugged the Beogram in and pressed start on the Apple Remote that connects to the Commander board and the carriage started moving. After it had moved sufficiently to reveal the small plastic fixture that holds the output board in place, I unplugged the unit and bolted the grounding connector of the RIAA board on top of the plastic part. The bolt goes directly into the enclosure, i.e. this is a good spot to make a system ground connection:

The last step was the installation of a new hood (acquired from the Beoparts Store in Denmark - these hoods are faithful reproductions of the original ones, made by injection moulding - very beolovely!). The first step was the removal of the hood hinge assembly from the scratched up original hood. To get to the screws one needs to remove the aluminum trim from the sides of the hood. This can usually be done with a razor blade that is forced in-between the trim and the plexiglass:

After unbolting the hinge assembly, I removed the actual hinges and checked them with my template that I recently developed after bent hinges led to the catastrophic failure of one of these hoods. These hinges passed with flying colors and fit perfectly onto my template:

So, on to the installation. I put the hinges back into place and then prepared the reproduction aluminum strip for hood. I usually make a small mark across a strip of blue tape and the aligned aluminum strip with a pencil:

That helps aligning the strip once the hinge has been bolted in. This shows the final result after installing the aluminum strip:

Very nice! This Beogram is ready for pickup! What better reason could there be for a roadtrip from Oklahoma to Albuquerque?!?!...;-)

Beogram 4002 (5503): Complete Functional Restoration

This post describes the restoration of an AC-motor Beogram 4002 (Type 5503), which I recently received from a customer in Oklahoma. My initial assessment of this unit was posted earlier here.

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

When I received the unit it came with a few loose parts, one of them the spring of the shut off (SO) switch. This shows the switch without the spring:

Luckily, I was able to reinsert it and the switch still worked properly:

the first step of the restoration focused as usual on cleaning and re-lubricating the moving parts of the carriage assembly: 

I removed all the parts partaking in arm lowering and carriage translation:

This shows the components before I cleaned them in an ultrasonic cleaner:

With the carriage up, it was the perfect moment to rebuild the carriage PCB. This shows it in its original condition:

This unit had an incandescent bulb in the carriage position sensor. This shows the bulb after removal of its housing:

I replaced it with a white LED and a 3.3k resistor (the bulb runs on 24V):

This shows the LED implanted, as well as the new capacitor and solenoid resistor that also need replacing on this board:

In the meantime the parts had finished their cleaning process in the ultrasonic:

As usual, the solenoid arm extension was cracked around the rivet:

I replaced it with a 3D printed part:

An important item is the replacement of the damper gasket. This shows a new rubber washer installed:

This ensures that the arm lowering process is consistent. The original washers are often hardened or deformed, which can cause intermittent arm lowering with much less damping than usual. A hair raising experience when you have a $600 cartridge on the arm!...;-)

After re-installing all cleaned parts, I focused on the damper-to-tonearm linkage, which has its pivot point located on the sensor arm assembly. The linkage can be seen from the back of the arms. It is the small lever that pokes out from the V-shaped notch in the arm that is attached to the back of the tonearm counterweight:

For lubricating the pivot point the sensor arm needs to be unbolted from the carriage:

After cleaning and lubricating I put everything back together and re-installed the sensor arm assembly. As usual the small copper plate that helps the arm to laterally move when it is up was loose due to degraded double sided tape. I cleaned it and epoxied it back into place:

The final step was re-aligning the arms. They need to be parallel and orthogonal to the carriage rods:

As the final 'carriage task' I replaced the cracking-prone carriage pulley with an aluminum replica:

This shows the carriage back together:

The next step was restoring the AC platter motor. It is shown here below the big reservoir and motor capacitor cans:

I extracted the motor

and took it apart by drilling out the rivets that hold it together:

I immersed the enclosure halves in motor oil and pulled a vacuum. As usual strong bubbling started as the air was extracted from the motor bearings and various other porous components:

While the oil infusion process was proceeding I focused on restoring the remaining parts of this Beogram. I removed the output board 

and replaced the output relay and its time constant defining capacitor:

I also installed a switch with which one can connect system and signal grounds in case there is a hum. This is often a good way to get rid of hum when connecting a Beogram to an amplifier with RCA inputs.

Then I removed all other components from the enclosure

so I could vacuum out all the fragments from the completely decayed transport lock bushings. This photo shows the fragments around a lock that was removed:

I vacuumed everything out:

While the enclosure was empty, it was a good moment to replace the power transistors of the AC motor push-pull stage. I replaced them with stronger TIP41/42 types:

I also replaced the solenoid transistor with a new TIP41C, a high voltage version of the original TIP41:

My hope is that the higher voltage version will withstand the stresses imposed by the solenoid better.

Then it was time to put the floating chassis back in with new transport lock bushings. This shows the Beolover replacement bushings. They are made from two halves that can be installed easily by simply using one half in from the bottom and the other from the top:

This shows one bushing installed on the extracted chassis::

and after putting the chassis back into the enclosure:

Next came the restoration of the main PCB:

I usually replace all electrolytic capacitors, all power transistors, the RPM trimmers and the high gain transistor of the sensor arm circuit:

There are usually also two capacitors soldered to the copper side of the PCB. This shows the original tantalum types:

I replaced them with modern capacitors:

Then I focused on replacing the reservoir and motor capacitors. This shows the installed new capacitors neatly organized by a 3D printed fixture:

This shows the backside of the assembly as well as the re-assembled AC motor

There were still three light bulbs that needed to be replaced: First I focused on the two in the RPM adjustment panel. This shows the extracted panel from the back:

I removed the bulb covers:

As usual the 33 RPM cover showed traces of heat deformation. Clearly a result of mainly playing 33 RPM records...

I removed the bulbs and installed the Beolover LED assemblies. They solder directly to the bulb solder terminals:

They do not interfere with the bulb covers. This shows the covers re-installed:

The last bulb to be replaced was in the sensor arm compartment. This shows the pulled out compartment with the original bulb installed and the Beolover LED assembly next to it:

This shows the LED board installed and the extracted bulb:

This Beogram had the usual cracked plinth guidance washers:

I replaced them with 3D printed nylon replicas:

The black one goes up front so it cannot be seen through the crack between enclosure and plinth. This shows one of the white ones installed on the sides of the plinth:

Now it was time to do some measurements. First I checked the motor AC signal. This shows the ~57 Hz signal that is to be expected for 45 RPM,

and this the ~42 Hz signal for 33 RPM:

Next was the adjustment of the tracking feedback:

Unfortunately, at this point I had to realize that this deck was not tracking! A visual inspection of the circuit board that connects the tracking sensor assembly to the main circuit revealed a crack that severed the photo resistor in the sensor from the main circuit:

I soldered two bridges in,

which restored the tracking function. After adjusting the tracking feedback I set the bias for the sensor arm transistor (TR9). I usually install a 5MOhm trimmer replacing the fixed 1MOhm bias resistor (R33) so I can precisely dial in the 4V at the collector that the manual specifies:

After moving the adjusted trimmer 'below deck' I installed the platter and measured the sensor response at the collector of TR9. I saw a healthy >7V amplitude which is an A grade!:

All good in the important record detection department!

Next I adjusted the platter arm distance and leveled the platter relative to the arm movement. Then the floating chassis was adjusted to yield a platter that is flush with the surrounding aluminum panels.

Once these adjustments were completed I calibrated the tracking weight of the tone arm. First I replaced the circlip of the counterweight adjustment screw

With a M3 nut:

Then I calibrated the tracking weight dial to be reasonably accurate around 1.2g, which is the typical weight at which B&O cartridges track best:

Then it was time to adjust the arm lowering limit:

This is an important adjustment that acts as a safeguard for the case of a malfunctioning record detection circuit, which might permit the arm to be lowered onto the platter without a record present.

At this point I realized that this Beogram 4002 5503 had the typical wavy background in the 33 RPM adjustment scale:

I removed the RPM panel once more and opened it up. This shows the white background of the 33 RPM scale. 

The heat load from the bulb did not only deform the bulb cover as seen earlier, but also the plastic foil that serves as background. I replaced both 33 and 45 backgrounds with cut to size portions of 3M white electrical tape:

After reassembly the background was pristinely uniform:

Then I finally replaced the original corroded DIN 5 plug

with a modern all-metal type fitted with gold plated terminals:

The next step was running a 24 hrs RPM test with the BeoloverRPM device, which allows logging the RPM in 10s steps. This is the curve I measured:

An excellent result. Though as usual, since the AC motor Beograms only very rarely have issues with RPM stability. A consequence of the classic synchronous motor based design.

Beolovely! And now it was finally time to give this Beogram a first spin! I selected one of my favorite Eddie Henderson records, "Comin' Through" that he recorded in 1977 (Capitol Records ST 11671). Of course this vintage record was ultrasonically cleaned using a CleanerVinyl ProXL setup to restore it to its original glory! A perfect match for this beautiful Beogram 4002:

It played beautifully with the rare MMC6000 cartridge that came with it.

The next step will be installing the Beolover Commander remote control system to protect the still very nice keypad of this Beogram, as well as an internal Beolover RIAA preamp that will replace the output board and will allow connecting this Beogram to any high-level amplifier inputs like AUX or DVD. Perfect for using this classic deck with a modern amp that does not have a dedicated phono input anymore.