Beogram 4002 (5523): Adjustment of Platter and Sub-Chassis Alignment, Installation of New Transport Lock Bushings and Adjustment of the Tonearm

After restoring all mechanical and electronic functions of the Beogram 4002 (5523) that I am currently working on it was time to give this baby a spin, and for that I wanted to have platter, sub-chassis and tonearm perfectly aligned to specifications. I started out by aligning the sub-chassis to be in the center of the transport locks. It turned out that a previous 'specialist' had installed the transport locks in a wrong way by not aligning the 'feet' of the lower locknuts with the matching cavities in the cast enclosure bottom. This prevented me from doing the adjustment. While I had everything apart I also put in new bushings since the original ones were completely deteriorated as indicated by the many pieces of orange plastic debris throughout the enclosure:

This shows the left lock with missing bushing:

This shows the new bushings installed in the left transport lock:

and here in the front lock:

There is a video about installing new transport lock bushings in my Beogram 4002 playlist. The bushings can be ordered directly from my Shapeways store. This is the link to the part. Two are needed per transport lock since one half is installed from the top and the other from the bottom.

After rebuilding the locks I was able to do the adjustments. There are two videos on my YouTube channel that show how to adjust the platter bearing and the subchassis (in a Beogram 4000, but the process is very similar in the 4002). This shows the Beogram after the procedure. The platter is flush with the surrounding aluminum panels and the platter is also centered within the main panel.

The final step was to adjust the arm lowering limits and then the tracking force. There is another video on my youTube channel that shows how to adjust the lowering limits. This is a very important procedure since the control system of the 4002 cannot guard against photosensor failure in the sensor arm. If the sensor fails the arm will be lowered whether there is a record or not, possibly endangering a very expensive cartridge. The correct adjustment of the arm lowering limit can prevent stylus failure if that happens.

The final step is always to adjust the tracking force to specifications. There is yet another video that shows this process. Here are a couple of impressions. I always start out by replacing the flimsy locking washer that holds the counterweight adjustment screw in the back of the arm assembly with a M3 nut and a washer. The original setup is way too wiggly for my taste and virtually guarantees that the adjustment changes whenever the turntable is moved. Not good for shipping at all. This shows the original setup:

and here after installing the nut and the washer:

this allows to reliably lock the zero force adjustment in place, which results in a stable weight scale reading on the small adjustment wheel.

After putting in the nut I adjusted the counter weight to yield 1g when the adjustment wheel is adjusted to 1g. This is better than adjusting the weight to yield zero for zero setting, since the adjustment wheel is not fully linear in its scale. Since most cartridges are in the 1-1.25 g tracking weight range, it is good to use 1g or 1.2g as center point for the calibration.

Then it was time to adjust the final setting with my B&O tracking force gauge:

and then it was finally time for some bliss: Playing one of my favorite records on this deck: Yellow Fields by Eberhart Weber on ECM.

Beogram 4002 (5523): Replacing the Incandescent Light Bulbs of the RPM Trimmer Scales with LEDs

Today I replaced the incandescent light bulbs that illuminate the RPM trimmer adjustment scales in the Beogram 4002 (5523) that I am currently rebuilding. I installed my custom designed SMD LED assemblies. LEDs last much longer than incandescent bulbs, i.e. this is a desired upgrade if long term use of the Beogram is the goal. This shows the latest re-design of the LED boards before installation:

These assemblies are available to other enthusiasts. This video shows how to install the LED boards. The first step is to take out the trimmer panel and remove the light bulbs:

Then the LED PCBs can be implanted:

The boards are designed that the original covers still fit perfectly over them:

Then the panel can be re-installed. These two pictures show the LED boards in action. Note the red scale hands. They show up red since the LED replacements are based on red/green bi-color LEDs whose intensities are calibrated to yield incandescent lookalike light, while containing red photons that can be reflected by the red scale hands.

If single color amber LEDs are used this does not work and the hands show up grayish and only turn red if there is red-containing light present from other sources such as incandescent room lights. 

Beogram 4002 (5523): Rebuilding the Control System and RPM Stability Qualification with the BeoloverRPM Device

After fixing the basics (tracking system and platter motor) in the Beogram 4002 (5523) that I am rebuilding right now it was time to get the electronic control system up to spec. An important part is to replace the electrolytic capacitors, replace the baseline RPM trimmers and the RPM and output relays. I also installed a grounding switch that allows to connect system and signal grounds, which is often helpful if there are ground loop/humming issues.

Here are a few impressions: 

This shows the main PCB before rebuilding:

A detail shot of the RPM relay and trimmer section before restoration:

These were the days when they still made relays in Germany...;-). Anyway, after 40 years even a Siemens relay has corroded contacts, and it is a great idea to replace it with a modern encapsulated Japanese quality relay. Another important upgrade for these turntables is to replace the single turn RPM trimmers with 25x multi turn units. Only such trimmers allow a precise RPM calibration. This shows the new relay and the two 33 and 45 trimmers:

They are implanted in a way that their trimmer screws are accessible from the other side of the PCB, that one can adjust them while the PCB is installed.

This shows the main PCB after rebuilding together with the exchanged parts:

I am always a bit sad when the colorful Ta capacitors are replaced by drab modern black aluminum cans. But it is a good idea to exchange the Ta units with modern Japanese 105C grade components since they can literally go up in smoke if their age related failure mode is a short circuit between their electrodes.

After doing the main PCB it was time to focus on the output board that carries the output relay. this shows the original board. It has the same Siemens relay like on the main PCB:

This shows the board after replacing the relay and putting in a new delay capacitor, and doing the ground switch upgrade:

The last step of the overhaul of the electronic system was to deoxidize the contact tabs in the keyboard switches:

This deck has unadulterated tabs, so I did not have to take them out for straightening. I pulled 2000 grit sand paper through the contact areas to clean them from oxidation. Then I coated the tabs with DeoxIT D100 which I applied using a cardboard strip coated with it.

After this it was time to put everything back together and check the motor RPM and do an adjustment of the baseline RPM settings with my recently developed BeoloverRPM device:

After adjusting the 33 and 45 RPM setting to spec it was time to do a RPM stability test. The BeoloverRPM device allows to log the RPM over many hours in 10 sec steps. It is also sensitive to sudden deviations and registers them at any time they occur via an analysis of the standard deviation of the measurement. Here is a graph of the RPM performance of this unit over about 8 hrs:

This is a pretty good result as far as I can tell. There are some small variations in the 0.05% range, which is about the 'wow and flutter' spec stated in the service manual. There is also a slow superimposed RPM drift of a similar magnitude, which may be temperature related.

Since I currently do not have any way to qualify the measurement error of the BeoloverRPM device other than putting it into my Beogram 8000 with uProcessor controlled RPM, I am thinking that the actual variations are probably a bit smaller than what is shown here since any measurement errors should add to the actual variations since they are independent.

Anyway, after this test, I plugged it into my Beomaster 6000 4-Channel and listened to my latest vinyl acquisition, "Aqualung" by Jethro Tull (Steven Wilson Remix), and thought that this deck sounds pretty lovely! This is Beolove!

Beogram 4002 (5523): Restoring the DC Platter Motor

Today was 'Motor Day' for the Beogram 4002 (5523) that I am rebuilding right now. The initial evaluation of this unit indicated the need for a rebuild due to the fairly loud running noise of the motor. It seems that most DC 4002s need some attention in this department these days. The sleeve bearings in the DC motor are usually dry due to aging lubricants, and so one needs to take the motor apart, clean it and re-lubricate the bearings. So I took the motor out and took it apart:

This photo shows the upper sleeve bearing after taking the rotor out:

and this one the lower bearing together with the feedback coils and the brushes:

This one shows me lubricating the upper end of the shaft:

and this one while cleaning the commutator with a fiberglass brush:

After putting the motor back together a test revealed that it ran much more quietly again. On to rebuilding the electronic system.

Beogram 4002 (5523): Rebuilding the Arm Lowering Mechanism, and Tracking Sensor Bulb Replacement and Adjustment

The first thing to do with a Beogram 4002 is usually a rebuild of the arm lowering mechanism and an adjustment of the tracking system. In this case the mechanical setup suffered from hardened lubricants and the tracking sensor sensitivity was much too high causing a runaway carriage after lowering the arm. Here is a picture of the solenoid and damper assembly:

The first step was to take it apart and clean and re-lubricate everything:

There is a video that shows the tracking sensor adjustment procedure in detail. After putting everything back together, I took the sensor arm out to get to the damper-to-arm linkage:

This video shows how to get to the damper to arm linkage and re-lubricate it. After putting things back together the tonearm aligned again with the sensor arm by means of the notch in the plate on the back of the counter weight assembly:

If everything is done properly, the arms should be fully parallel after this procedure and perpendicular to the back of the enclosure:

The next step was to fix the tracking system. I usually recommend to install a LED based light source into the system to ensure long term stability. This shows the original tracking sensor light source:

And here is the SMD LED based replacement unit that I recently designed:

The original incandescent unit is also shown for comparison. Like all my parts this assembly is available to other enthusiasts.

After putting in the new light source, I adjusted the tracking system feedback loop sensitivity. After a coarse mechanical adjustment using the excenter behind the light source, I fine tuned the sensitivity using the blue trimmer potentiometer that is integrated in the LED light source:

There is a video that shows the tracking sensor adjustment procedure in detail. It is a good idea to do this adjustment with an unwanted LP (some free jazz by Sam Rivers is a great choice for this task) and not your best cartridge. It is possible that the carriage drags the stylus across the record if one is not careful while doing the adjustment. After these procedures the tonearm and the carriage behaved normally again. On to a rebuild of the electronics.

Beogram 4002 (5513): A New Arrival on Beolover's Bench

Over the Holidays another Beogram 4002 (5513) arrived for some TLC. Today I did a first evaluation. The packing job was excellent and featured some new ideas how to safely package a Beogram. Here are some impressions:

The hood was filled with soft foam blocks to hold the sub platter and the RPM panel down:

One of the foam blocks contained the MMC20E cartridge, which traveled well:

Here an impression after taking it out:

I appreciated the precisely cut cardboard that held the sub-platter in place. The arm support also worked very well:

I took the hood off and the back part of the enclosure to give the inside an examination. It all looked original and pretty clean. Then I plugged the unit in and pressed start. The carriage started moving, but at the 30cm set-down point it lowered the arm, but then kept going at a rapid pace. An examination of the tracking system revealed a bent tracking sensor aperture which is stuck in the bulb housing. 

So that definitely needs rebuilding. Also the arm linkages are somewhat hard to move due to the usual hardened lubricants. Nothing that a good cleaning and re-lubricating could not fix.

I also noticed that the motor runs pretty rough, so it also needs to be taken apart and cleaned and it needs to get some fresh lubricant injected into its sleeve bearings.

Other than that, as far as I can tell right now this unit is in pretty good condition mechanically.

Cosmetically, the plinth is in great condition, the aluminum panels could do with a deep clean and the keypad has the usual three-finger usage pattern, but not too bad.

The hood, as usual, could do with some polishing.

All in all no obvious show-stoppers. It seems this unit is a great starting point for a restoration. This Beogram has an excellent potential to be as good as new once I am done with it.

Beogram 4002 (5513): Adjusting the Sub-Chassis and the Platter, and RPM Calibration

Today I it was time to give the Beogram 4002 (5513) that I am currently reviving a properly adjusted platter and sub chassis. The goal is to adjust everything that the aluminum surface of the platter is flush with the aluminum panels surrounding it, while having the sub chassis centered between the upper and lower limits of the transport locks and the arms being also parallel to the aluminum surfaces. This is usually a pretty delicate process since so many things need to align. I have now a bit of experience with this and so after a while this Beogram looked very nice and up to spec. I recently made a couple videos that demonstrate this process:

Once the platter was adjusted I did a baseline RPM adjustment for 33.33 and 45 RPM using my recently developed BeoloverRPM device. Here is a picture of it in action:

This shows the readout after I already had adjusted 33.33 and then did 45:

Stabilizing
Measurement	starts
time:	0:0:9	RPM:	33.381
time:	0:0:20	RPM:	33.3782
time:	0:0:31	RPM:	33.3904
time:	0:0:42	RPM:	33.3987
time:	0:0:53	RPM:	33.4052
time:	0:1:4	RPM:	33.3937
time:	0:1:15	RPM:	33.4039
time:	0:1:26	RPM:	33.3882
time:	0:1:37	RPM:	33.3958
time:	0:1:48	RPM:	33.3817
time:	0:1:59	RPM:	33.3982
time:	0:2:10	RPM:	33.4025
time:	0:2:21	RPM:	33.4117
time:	0:2:32	RPM:	33.4088
time:	0:2:43	RPM:	33.3933
time:	0:2:54	RPM:	33.3916
time:	0:3:5	RPM:	33.3879
time:	0:3:16	RPM:	33.3815
time:	0:3:27	RPM:	33.4003
time:	0:3:38	RPM:	33.4095
time:	0:3:49	RPM:	33.4057
time:	0:3:54	RPM:	35.24
time:	0:3:55	RPM:	38.32
time:	0:3:56	RPM:	40.9
time:	0:4:0	RPM:	44.4733
time:	0:4:11	RPM:	44.8362
time:	0:4:22	RPM:	44.8325
time:	0:4:33	RPM:	44.8564
time:	0:4:44	RPM:	44.8543
time:	0:4:55	RPM:	45.0447
time:	0:5:6	RPM:	45.1634
time:	0:5:17	RPM:	45.1921
time:	0:5:28	RPM:	45.1968
time:	0:5:39	RPM:	44.8451
time:	0:5:50	RPM:	44.8174
time:	0:6:1	RPM:	45.2279
time:	0:6:12	RPM:	45.2203
time:	0:6:23	RPM:	44.7694
time:	0:6:34	RPM:	45.1452
time:	0:6:45	RPM:	45.2124
time:	0:6:56	RPM:	45.1949
time:	0:7:7	RPM:	45.1759
time:	0:7:18	RPM:	45.1953
time:	0:7:29	RPM:	45.2055
time:	0:7:40	RPM:	45.1998

It turns out that it is pretty difficult to adjust the RPM precisely with the standard single turn RPM trimmers that are in the Beogram originally. You can see at the and how I tried to get close to 45, but I always missed it by 0.2 or more by just very slightly moving the trimmer. This demonstrates that it is a great idea to put in multi-turn trimmers to get this right. On the other hand, I think it is difficult to hear such small difference...so this deck sounds now pretty good, especially with the lovely MMC20CL cartridge that came with it. I am listening to 'Song for My Father' by Horace Silver on Blue Note on it right now while writing this post! Wonderful!

I will give this Beogram some more listening to make sure there are no intermittent issues, but I think it is ready for duty again. This is Beolove!