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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Tuesday, February 21, 2023

Beogram 4004 (Type 5526): Complete Functional Restoration

This post covers the work done on the Beogram 4004 (5526) from California that I recently put on my bench. My initial assessment of this unit is posted here.

This shows the Beogram with the panels and platter removed:

I started out with the DC platter motor. Pretty much all of them need their bearings re-infused with oil at this point in time. This shows the motor as installed:
I extracted it and took it apart to get the bearings out. They are on the black pad up front:
I put them into motor oil and pulled a vacuum. Immediately, strong bubbling began:
The bubbles represent air drawn by the vacuum from the porous bearing material. Each bubble makes room for an amount of oil to diffuse into the bearing during this process.
While this process was going on I focused on the rest of the Beogram. I removed all the essential mechanical parts from the carriage, i.e. the arm lowering setup as well as the rods and spindle for moving the carriage:
I thoroughly cleaned everything and also installed a new rubber gasket in the damper plunger:
I realized a while ago that these rubber discs can harden and then the damper does not damp the arm lowering motion reliable anymore. It can come to intermittent failures where the arm drops suddenly without or not enough damping, and that can result in scary moments where one fears for the cantilever.

Another item to take care on the carriage is replacing the bulb in the tracking sensor with a LED assembly. This shows the original black bulb housing on top of the sensor:
I removed it, which revealed the aperture that controls the light on the sensor depending on the arm deviation from normal:
I installed a Beolover tracking sensor LED light source:
The small white box is a trimmer that allows controlling the light intensity of the LED. This is very helpful for fine-tuning the tracking feedback.
Another item to be replaced on the carriage is the usually cracked plastic pulley that is driven by the carriage motor. In this case it already had received an impressive repair job:
I extracted it and replaced it with a precision turned aluminum pulley:
Beolovely! The final stroke of the carriage rebuilding effort was to re-lubricate the damper to arm linkage that often seizes due to hardened lubricants. Unfortunately, one has to take the sensor arm out to get to the linkage. This shows the arms from the back: 
And here with the sensor arm assembly removed and the linkage taken out:
I lubricated the pivot point and then put everything back together, making sure the sensor arm was again parallel with the tonearm.

After completing my work on the carriage I moved on to the electronics. A while back I started replacing all power transistors along with the capacitors and certain other items since I had received a few units back over the years where one or more of these transistors had given out after I restored the units. Live and learn....The Beolover shall not rest until his restorations are 100% perfect!..;-).
I usually start the main-PCB restoration now by replacing the two power Darlingtons that are accessible from the solder side, i.e. from the top. It is best to replace them while the board is still bolted in. This shows IC4 as example:
Someone already had replaced it with a BD898 at some point in the past. To be on the safe side I replaced it anyway with a new TIP107, a beefier version of the original TIP125 pnp:
After also replacing IC1 I took the board out and replaced all electrolytic capacitors, the complete RPM adjustment section, the sensor arm transistor and biasing resistor and the H-bridge power transistors. This shows the completed board and the extracted parts:
A detail shot of the 'RPM section' with the new relay and new RPM 25-turn trimmers for a more precise RPM adjustment:
Before this board was ready for duty again the sensor transistor had to be properly biased: I adjusted the newly installed bias trimmer to get 4V at the collector of the transistor
And then I moved it to the component side (small blue horizontal box at lower end of photo):
The other board that needs rebuilding in the 4004 is the output board. This shows it in its original condition:
And here rebuilt with a new output relay and delay capacitor:
This Beogram had already been updated with new transport lock bushing from the beoparts store. In my opinion they are a bit thicker than they should be, which limits the range of motion of the floating chassis when it is unlocked. The Beolover's own flavor of this part is much thinner (but also less rubbery, since it is made from nylon). But this can definitely be used:
Unfortunately, when they were installed, the debris from the degraded original bushings had not been fully removed, so I took the floating chassis out that I could give the enclosure a good vacuuming. It can be a problem if there are crumbs of the original bushings under the floating chassis, since they can impede the motion of the chassis:
And indeed, there were some pieces under the chassis:
I put the chassis back in and also replaced the original reservoir capacitor
with a new (smaller) replacement, held in place by a 3D printed adapter and the original clamp:
After this it was time to replace the remaining incandescent bulbs. First I tended to the RPM panel which contains two bulbs. This shows the removed panel with the original bulbs installed as well as the to be implanted Beolover LED assemblies:
This shows the LED PCBs installed:
They directly solder to the pads where the bulb wires are soldered in. The covers install exactly like before:
The final bulb to replace was the one in the sensor arm. This shows the original bulb with the LED assembly:
I removed the bulb and installed the LED:
This shows the LED in action. It is a warm white type and so emits enough red photons to illuminate the B&O logo properly:
After this it was time to do all the adjustments. As usual I adjusted platter height and level relative to the arms first. The next step was to get the floating chassis to cooperate to get the platter perfectly level with the surrounding aluminum panels. This can take significant time until it is perfect. After this was done, I focused on the arm adjustments. I usually replace the flimsy circlip that holds the counterweight adjustment screw in place with a nut. That way I can lock the calibration in place that it survives the rigors of shipping. This shows the square nut in place:
Then I adjusted the arm lowering limit with the goal that the needle will miss the platter ribs should the arm ever be lowered on the spinning platter due to a malfunction in the record detection circuitry or similar:
Then I calibrated the tracking weight dial to be accurate around 1.2g. It is notoriously difficult to get this scale completely right, and so my recommendation is to always check the weight with a digital scale:
On to adjusting the tracking feedback:
After all these adjustments were in place I checked on the motor bearings, and after about 4 days they had stopped bubbling. This indicated that the infusion process had completed. I extracted them from the oil:
Then put the motor back together and installed it int the Beogram for a 24 hrs RPM stability test with my BeoloverRPM device:
The BeoloverRPM allows logging the RPM for extended periods of time. This is the curve I measured during ~24hrs:
This is a pretty decent curve, but we see that the bearings are still settling in their new positon, hence some small peaks and a small step can be seen. It can be expected that this will improve after another 100 hours of runtime or so. 
Before giving this deck a first listening I replaced the original convertible DIN7 with a new gold plated DIN5:
My customer had decided that he did not really need the early Beolink functionality that was introduced with the 4004. It uses the two additional pins on the original DIN7 for a simple form of data transmission to control start and stop of the Beogram via the remote control of a Beomaster 2400 receiver.
The original DIN7 plugs have two screwed in pins that can be removed to convert the plug to a DIN5 that will fit into non-B&O DIN receivers. In this case this conversion had already been done at some earlier point, and as usual the pins went missing.

Then it was finally time to clean the aluminum surfaces and put the deck back together for a first listening!
I selected one of my favorite MPS records, George Duke's "Faces in Reflection" from 1974 (MPS MC22018). Of course it was ultrasonically cleaned with a CleanerVinyl ProXL setup on a UC-3360 multi-frequency cleaner prior to playing it. Here is an impression:
Beolovely! I will now play this Beogram 4004 for a few days and if nothing else comes up, it will soon be time to send it back to its owner.

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