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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, May 7, 2024

Beogram 4004 (Type 5526): Full Functional Restoration of a Trade-In

I recently accepted some trade-ins towards a Beogram restoration. This post discusses the restoration of one of the units, a Beogram 4004 (Type 5526).

This fully restored Beogram 4004 is now available for purchase.

This shows the Beogram as extracted from the shipping container. Since it traveled in a Beolover double box, everything went well:

Unfortunately, the hood of this unit was completely shot with both hinge sides beyond repair:
Minus the hood, this unit was in pretty good condition with almost flawless aluminum panels and a platter that has only minor scuffs. Even the keypad is in almost new condition with only very light finger smudges:
Sadly, one of the plinth corners is a bit shaved, i.e. this plinth has to be replaced:
Under the panels everything looks original, a perfect starting point for a full restoration:
As in most Beograms of this vintage the carriage pulley was cracked and someone tried to glue it:
This never works and it is much better to replace it with a precision machined Beolover aluminum pulley!
Further inspection yielded the usual degraded transport lock bushings as is evident from the many orangish fragments strewn around the enclosure:
After this visual inspection, I plugged the unit in and pressed start. The carriage sluggishly started moving to the LP setdown point and the solenoid engaged. Encouraging signs!

As usual, I started with the DC platter motor. It can take a few days until the oil-infusion of the motor bearings is complete, i.e. the rest of the deck can be restored in the meantime.
This shows the extracted motor:
I disassembled it to get the bearings out:
The bearings are the two small items on the black pad upfront. I immersed them in motor oil and pulled a vacuum. Immediately, strong bubbling started:
This bubbling comes from air being drawn from the pores of the Oilite bearing material. As the air is sucked out, oil diffuses into the vacated space. This replenishes the oil storage in the bearings getting them ready for another few decades of service. While this process was underway I focused on the rest of the deck. 

I started with the mechanical systems on the carriage. The arm lowering mechanism and the carriage transport assemblies are often encrusted with hardened lubricants and dirt. This shows the original condition of the setup:
I removed all the moving parts:
This shows them ready for the ultrasoinc cleaner:
And after about an hour of cleaning:
Beoshiny! Then it was time to put everything back together with fresh lubrication. Before I re-assembled the damper I put in a new plunger gasket:
This ensures a consistent arm lowering speed. The original gaskets are often hardened or deformed, which can cause sudden high-speed arm droppings. A fairly hair-raising experience when a $800 cartridge is mounted on the arm...;-). This shows everything back in place:
I realized that the carriage motor was wiggling in its enclosure. I opened it up and found this mess: Completely degraded damping foam:
I replaced it with some polyurethane foam and re-assembled:
Then I implemented a new aluminum pulley and carriage belt:
Then I replaced the incandescent light bulb in the tracking sensor with a LED assembly. This shows the original setup. the bulb is in the black box in the center of the picture:
I removed the bulb housing, which revealed the aperture that controls the amount of incident light on the photocell below depending on the arm deflection as the needle moves inward on the record:
This shows the (red/green) Beolover LED assembly in direct comparison with the light bulb. The small SMD LED is in the same location like the filament of the bulb:
This shows the LED assembly installed:
The final task on the carriage was re-lubricating the damper-to-arm linkage, which is bolted to the sensor arm assembly. You can see the linkage sticking out in the V-cut on the part that is bolted to the back of the tonearm counterweight:
I unbolted the sensor arm assembly and removed the linkage:
Then I cleaned the pivot point and re-lubricated it prior to re-assembly. As usual, the small copper pad that helps the arm move laterally when it is up came loose after a light tug with my tweezers:
I removed the degraded double-sided tape and glued it back into place with a dab of epoxy.

The next step was rebuilding the electronics. I usually start out with the power Darlingtons that are mounted on the solder side of the main PCB. This shows IC1, which usually is a TIP120:
I replaced it with a stronger TIP102 and added a (yellow) 100nF capacitor to its emitter:
This quenches some unwanted high-frequency oscillations that can be introduced by modern TIP packages in this circuit configuration. I also replaced IC4 with a TIP107 and then removed the board. I usually replace all electrolytic capacitors, power transistors, RPM relay, RPM trimmers, and the sensor arm transistor. This shows the rebuilt board with the extracted components:
A detail shot of the RPM section with modern 25-turn trimmers for precise RPM calibration and the Beolover RPM relay replacement assembly:
Then I removed the keypad to get the output PCB out. This shows it in its original condition:
A detail shot of the output section consisting of output relay and delay circuit:
I removed all electrolytic capacitors and installed a new output relay:
As usual, I added a (red) switch that allows connecting signal and system grounds:
This is useful when there is a hum after connecting to an amplifier.
Then I removed the original reservoir capacitor
and the floating chassis. This left the empty enclosure ready to be purged of the many transport lock bushing fragments:
This must be the best example ever of degraded transport lock bushings! What a mess!:
I vacuumed everything out:
Then it was time to install new Beolover transport lock bushings:
They are very convenient to install. Simply push in one half from below
And add the second half from the top:
This shows the new bushing with the lock screw installed:
After putting the floating chassis back in with the new bushings, I installed a Beolover reservoir capacitor assembly:
In this case the original main capacitor was a regular single capacitor, i.e. all that was needed to be done was to solder the white and black leads of the power entry plug to the correspondingly labeled solder pads of the capacitor assembly and bolt it in:
After installing the output board and keypad I powered the Beogram up to adjust the sensor transistor to get 4V at its collector:

On to replacing the remaining incandescent light bulbs. First I did the one that is in the sensor arm. This shows the bulb still in place, together with the Beolover LED replacement and its alignment aid:
This shows the LED assembly installed:
After replacing the bulb I did a measurement of the sensor signal at the collector:
Every dip of the trace corresponds to a platter rib passing under the sensor. This is how the electronics determine whether it is safe to lower the arm (no dips) or not (dips). The amplitude of the dips should be >5V, which was nicely exceeded in this Beogram!
The final bulbs were in the RPM panel above the keypad. This shows the panel removed and flipped over, revealing the two bulb covers:
I removed the covers:
And then removed the bulbs:
Then it was time to solder in the Beolover RPM LED assemblies:
They directly attach to the solder points of the original bulbs:
The bulb covers can be re-installed after the exchange:
At this point the bubbling of the bearings had stopped, indicating that the infusion process was complete. I extracted them from the oil:
Then I re-assembled the motor and also replaced the damaged original pulley with a beautiful new Beolover DC motor pulley. This pulley is a faithful reproduction of the original pulley including its 'crown' bulge that holds the belt centered:
This shows the motor installed:
Next I focused on the adjustment of the platter height and parallelism, followed by an alignment of the floating chassis to get the platter flush with the surrounding aluminum panels.
After this process it was time to adjust the tone arm. First I adjusted the arm lowering limit. When lowered on the naked platter, the needle should miss the lowered parts of the platter ribs by about 1 mm:
This is a safeguard in case the arm gets lowered on an empty platter in case of a circuit malfunction.
After this I adjusted the tracking force. But first I replaced the flimsy locking washer that holds the screw in place that allows adjusting the counter weight position:
I usually replace it with a M3 square nut:
This allows fixing the weight calibration in place so it withstands the rigors of shipping.
I use a digital gauge to measure the tracking weight accurately. I usually adjust the counterweight in a way that the weight adjustment dial is accurate around 1.2g, the weight that most B&O cartridges demand:
Then I performed a 24 hours RPM stability measurement with the BeoloverRPM device:
In its 'slow' mode, the BeoloverRPM allows logging the RPM in 10s intervals for long periods of time. This is ideal for detecting intermittent RPM changes, which can be very difficult through listening to records. This is the curve I measured after 24 hrs:
This is a pretty normal result for the DC motor based Beograms. There is a slight longterm drift caused by temperature changes of the analog motor control circuit. The noise superimposed to the curve is partially a measurement artifact coming from minute variations of the spacing between the platter ribs. The BeoloverRPM measures the time between platter ribs passing under the BeoloverRPM sensor and it calculates the RPM from these measurements. Hence, if the spacing varies, the determined RPM varies proportionally.
This can be seen more clearly in a 'fast' mode measurement with the BeoloverRPM device, where each rib passing generates a logged measurement:
This curve covers about 60 platter rotations (~120 sec of measurement) and we see that the 'noise' is actually a pattern that repeats every 24 measurement points (there are 24 ribs on the platter...). This pattern varies in intensity which is caused by real variations ('wow and flutter') of the platter speed caused by the feedback-based control circuitry of the Beogram. From the amplitude of these sinusoidal variations it can be deduced that wow and flutter is about 0.1% for DC motor Beograms. That is 2x of the stated 0.05% in the Beogram service manual. This discrepancy may be a consequence of the entirely different way this was measured in the 1970s, where precise digital measurements were not possible yet. Whether they are 0.1% or 0.05% these fluctuations are much smaller than what humans can discern, and so nothing to be concerned about. This Beogram is ready for duty again!
Since this unit will be sold I did not put on a new output plug yet. This unit came with a still pretty nice original convertible DIN7:
These DIN7 pins can be converted to DIN5 in case the Beogram is not used with a Beomaster 2400 (which is able to remote control Beogram 4004s via the two additional pins). The two additional pins are threaded in, i.e. can be unscrewed and the plug becomes a standard DIN5:
This shows the two removed pins. The threads at their bottom end can be clearly seen:
After this educational inspection of a convertible DIN7 plug, it was finally time to give this beautifully restored deck a spin. I selected one of my favorite Grover Washington, Jr. records, "Inner City Blues" that he recorded in 1971 for the awesome Kudu label (KU-03). Of course this album was ultrasonically cleaned with a CleanerVinyl ProXL setup, which restored this lovely vinyl to its original glory. What a perfect combination!:
At this point you probably wonder why this plinth looks so awesome?!

I replaced the original plinth with the chafed off corner with a brand new solid Granadillo (aka 'Mexican Rosewood') frame. I think it looks very awesome!

The other issue with this trade-in was the completely shot hood. Unfortunately, the nice reproduction hoods designed by Martin Olsen in Denmark are currently not available due to some production issues. Therefore, I installed a 'new original stock' (NOS) B&O hood that I purchased from an Italian gentleman a few years back. Here are a few impressions of the final 'product' of my efforts:

A pretty lovely Beogram 4004 would you not agree?? But of course it is not perfect! Such is life!...;-). The NOS hood had a small flaw, a scratch up front:
It almost looks like a production flaw, and the hood I bought may have been discarded back then during inspection after production. But of course now, almost 50 years later, this hood is a valuable find that elevates this Beogram to an almost original like-new condition.



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