This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...
Saturday, April 30, 2016
The Beogram 4002 (5514) that I am currently restoring is making progress. In my opinion a Beogram restoration is only complete with a modern all-metal DIN 5 plug that has gold coated contact terminals. The original plugs are usually corroded and that is not a great thing for transmitting the precious signals from the MMC cartridge. Here is an impression of the original plug with oxidized terminals:
This shows the soldering job inside the new plug:
And here the final result:
Pretty, isn't it?? This is Beolove! On to adjusting the platter and sub-chassis...
Before I was able to adjust the platter and sub-chassis of the Beogram 4002 (5514) that I am restoring right now I needed to replace the disintegrated transport lock bushings. This deck had the orange type bushing and so it was not a surprise that they were gone:
Since the fragments were all over the place I took out the sub-chassis to make sure that there were none left underneath:
Rogue bushing fragments are sometimes an issue since the sub-chassis floats fairly close to the bottom of the enclosure, and if there are bushing splinters lodged between the chassis and the enclosure the chassis cannot float freely anymore, which impairs the vibration insulation of the turntable mechanism.
After cleaning things up I installed my 3D printed replacement bushings :
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 parts are needed per transport lock.
The next steps will be adjusting the platter and the chassis, and then do the tonearm weight calibration and arm lowering limit adjustment.
Thursday, April 28, 2016
A good day in Beolover's shop! Another Beogram 4002 (5513) looking sharp and performing like new! I finished up the unit by adjusting the sub-chassis and the platter to be freely floating and being flush with the aluminum surface of the deck. 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). Once that was done, I adjusted the tone arm lowering limit. There is another video on my youTube channel that shows how to do this adjustment. 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.
This shows the limit properly adjusted that the needle just misses the lower rungs of the platter 'ribs':
The final step was to calibrate the tracking force after upgrading the counter weight mechanism with an M3 nut. This shows the original setup with a circlip. Somebody added some glue to stabilize this normally pretty wiggly set-up:
I usually install a M3 nut and a washer, which allows to lock the mechanism after calibrating the tracking force, but makes it much easier to redo the adjustment should it ever become necessary again:
Once the zero weight is properly adjusted, the tracking force can be calibrated with a scale:
After this it was time to take this Beogram for a spin! I selected a recent acquisition from ebay, Idris Muhammad's absolutely wonderful 'Power of Soul' issue:
After cleaning this 'near mint' record with my recently developed CleanerVinyl record cleaning attachment for an ultrasonic cleaner it sounded like new again. In my opinion this is one of the best KUDU Records releases (KU-17). It is a beautifully arranged (Bob James) lush and melodic record that brings together some of the greatest jazz talent of the 70's. Grover Washington, Jr is in top form and even Randy Brecker sounds sharp and right on point (usually I am not such fan of his output, but here he is just awesome!)! Check out Loran's Dance and Piece of Mind. My only complaint is that these two tracks are not on the same side...;-).
O.k...pretty much done with this Beogram 4002! Polishing the hood is left, and I will need to find that perfect moment where a three-hour polishing workout on my work bench is just what I need...;-).
Tuesday, April 26, 2016
By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demonstrates how to take the motor apart and how to restore the Oilite brass bearings with an oil infusion under vacuum. If your Beogram has RPM fluctuations this is the video for you! Check it out:
The restoration of the signal path is only complete with a gold plated plug, and so I just did it for the Beogram 4002(5513) that I am restoring right now: This shows the sad original oxidized plug:
And here an impression of the internal configuration of the new Rean plug:
Well organized and pretty! And with the all metal enclosure on:
Even prettier! This is Beolove!
Monday, April 25, 2016
After rebuilding the DC motor and the control system of the Beogram 4002 (5514) that I am restoring right now, it was time to do a RPM performance test. I set up my BeoloverRPM device that allows the long-term logging of the platter RPM, and then did a 24 hrs test:
After the data was logged on my computer, I graphed it relative to a measurement that I took when I initially received the unit for restoration. This shows the two curves in comparison:
The red curve shows the performance before the restoration. The typical telltale sudden negative RPM spikes are visible that indicate failing brass sleeve bearings in the DC motor. This is very common for DC motor Beograms. In this case the spikes are still fairly moderate, but would have been audible since they are in the 1% range. The black curve shows the performance after rebuilding the motor and the installation of new RPM trimmers and RPM relay. The large spikes are gone and the variations are much smaller. There are still some variations, which are related to the intrinsically slightly erratic performance of the analog motor control system, which is affected by temperature changes and probably the moon phase (that was a joke...;-). Some Beograms show them others do not. At this point I do not have an answer why they sometimes occur. The good news is that they are fairly slow over time and also small enough that one cannot hear them. The short term 'wow and flutter' RPM changes (the high frequency 'noise' on these curves) are within the spec given in the service manual (0.05%). So this Beogram is back in business.
Beogram 4002 (5514): Replacing all Electrolytic Capacitors and Rebuilding of the Platter RPM Control System
After rebuilding the DC motor of the Beogram 4002 (5514) that I am restoring right now it was time to update the electronics. I usually replace all electrolytic capacitors, install new relays to further reduce RPM variations and give the RPM control circuit modern 25-turn potentiometers that the RPM can be adjusted reliably. It is important to replace the aging Ta capacitors since they can fail via short circuit and go literally up in flames. This shows the main board in its original condition:
After the rebuild it looked like this:
the extracted parts are on the left. This is a detail shot of the 'RPM section':
The old Siemens relay was replaced with my custom designed replacement relay based on a modern encapsulated Japanese SMD relay and a breakout board that precisely matches the pinout of the original Siemens relay. This shows the part in detail:
I have a similar part available for the National relays that can be found in certain 4002 units. They are available to other enthusiasts. Just send me an email of use the contact form.
After doing the main board I moved on to replace the reservoir capacitor. This shows the original can:
the two contacts at the front are the positive ends of two capacitors that have their common ground on the back:
Such double-capacitors are no longer available, and I usually replace them with a custom designed 3D printed fixture that holds two modern 105C grade capacitors in place and that fits to the mounting strap of the original capacitor:
This shows it installed:
On to PCB#8 (the 'output board'). This photo shows the original condition:
The output relay is also a Siemens version, i.e. can be replaced with the same relay as the RPM switch relay above:
I also added a grounding switch that allows to connect signal and system grounds in case there are humming issues when connecting to a amplifier with RCA inputs.
Sunday, April 24, 2016
While I am having the Beogram 4002 (5513) that lost its solenoid plunger on my bench, I decided to redo the DC motor. When I initially restored this deck I did not know yet that one needs to infuse the brass sleeve bearings with oil under vacuum if the fix is supposed to have lasting effect. Just putting some grease on the bearings quiets them down temporarily and stabilizes the RPM performance, but after a few weeks usually the effect of the grease wears off and RPM variations start occurring again.
Here are a few impressions of the process. The motor needs to be completely disassembled to get the bearings out (and more importantly, back in):
The next step is to infuse the bearings with oil under vacuum. I use a mason jar and a FoodSaver vacuum pump for that. As soon as the vacuum is established air bubbles arise from the bearings:
This is a result of the expansion of the air in the pores in the brass due to the low pressure in the jar. The escaping air makes room for the oil that can then diffuse into the bearing.
A typical Oilite bearing contains about 20% oil by weight. This is enough to provide an oil field on the bearing surface for many hours of motor operation.
Once the bubbles stop (typically takes about 12-24 hrs) the bearing is full of oil again and there motor can be reassembled. This shows the brushes carrier plate with the bottom bearing reinserted:
The top bearing is held in place with a ring whose tabs need to be forced back flat to hold the bearing in place securely. I designed a special tool for this task that allows me to use adjustable pliers to press the tabs down:
The red cylinder goes inside the motor housing and the orange part is used to press the tabs down against the red part. This results in a bearing that sits snugly in its cradle below the top shaft orifice:
Once the bearings are back in, the motor can be put together and the PCB soldered back on:
At this point the motor needs to be tested with a bench supply. It is imperative that the brushes carrier plate is installed in a way that the rotor rotation is not impeded. This can be reliably quantified by observing the current that the motor draws while spinning freely at 5V. In my experience the lowest current that can be achieved is below 30mA. If there is too much friction the current will be higher. If that is the case the bottom plate needs to be loosened and carefully retightened while turning the screws in small steps in sequence until they are tight. It can take a few attempts until the lowest current can be achieved. This shows my bench supply with the motor running after I was done with this process.
Once the current is right, the motor can be inserted into the outer noise canceling shell and then reinstalled in the Beogram.
It is a good idea to test the motor for a few hours to make sure that everything is stable and up to specifications. I did that with my BeoloverRPM device that allows to measure the RPM over time and log it via the serial port of a computer. This is the graph that I measured for this motor over about 8 hrs:
This looks as it should! This Beogram 4002 is ready to be shipped back! Hopefully this time it will stay away a bit longer!
Saturday, April 23, 2016
Oh well...a sad moment: A Beogram 4002 (5513) that I recently sent back to a customer already returned. A few weeks after a happy report of enjoying vinyls on the newly restored 4002 (via my recently developed internal Beogram RIAA pre-amp) an email reached me stating that the tonearm would not lower anymore. So the deck was packed up again and it came back to my bench. What I found was pretty astonishing:
If you look closely, you see that the solenoid plunger went missing. No surprise that the arm did not lower anymore...nothing to there for pulling the linkage that activates the damper, and with that the arm lowering mechanism. So I went looking for the plunger. After taking out the sub chassis
I finally found it:
The amazing thing here is that the end of the hook that grabs the linkage broke off...I never saw such thing before, but I guess material fatigue can hit the most unlikely places.
The only solution for this issue was to replace the solenoid with a unit from a parts 4002 that I bought on ebay a while ago:
After this implantation the mechanism worked again. While I had the sub-chassis out it became apparent that the transport lock bushings did not survive the return trip and that they needed to be replaced. This shows the detritus of the front lock bushing:
I should have replaced them during the first 'visit' of this Beogram, but they looked o.k. then and so I left them. I think it can be said with some certainty that all orange looking bushings need to be replaced at this point in time. The grey ones seem to survive better.
I replaced all three bushings with my nylon replacement parts printed by Shapeways:
Each bushing is replaced by two of these parts, one goes in from the top and the other one from the bottom:
This shows the left-side lock put back together:
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.
Allright...this Beogram is on the mend. However, before I send it back, I will give the DC motor my oilite bearing oil infusion treatment. When I initially 'rebuilt' the motor of this Beogram, I did not know yet about the necessity of infusing the brass sleeve bearings of the Beogram DC motors with oil under vacuum. This is the only way to re-lubricate the bearings with lasting effect that the motor can serve another 30 years...this is Beolove!
Wednesday, April 20, 2016
Most Beogram 4002 with DC motor need the motor rebuilt at this point in time. Sudden RPM drops or a noisy motor performance are signs that the time has come. In this particular Beogram 4002 (5514) the motor was fairly noisy when running without load. I rebuild all DC motors when I restore a 4002 since these problems will sooner or later hit all of these motors. The main cause for these performance issues are drained oil infused brass sleeve bearings with 'permanent' lubrication. these bearings are made from porous brass, which are infused with oil under vacuum. This type of bearing is good for many years until the infused oil runs out. While the motor is running the infused oil continuously replenishes the oil film on the bearing surface. The spinning shaft slowly distributes the oil to locations outside of the bearing, eventually depleting the oil.
Since such low voltage DC motors with appropriate inductive tacho control feedback appear to have vanished from the marketplace, the only solution is to replenish these bearings with oil to give the motor another lease on life. The extraction of the bearings requires a complete disassembly of the motor. Otherwise it is not possible to get the bearings back in properly. This shows the motor disassembled. The bearings are the two small round items in the 'front row':
Once I had the bearings out I immersed them in a mason jar and pulled a vacuum with a FoodSaver pump. Immediately, air bubble started emerging from the bearing indicting that the infusion process had started:
After 24 hrs the process had abated and no more bubbles could be noticed:
I read that about 20% of the weight of such a bearing is the infused oil.
I extracted the bearings from the jar and reinstalled them. This shows the bottom bearing installed in the brushes carrier:
The top bearing needs to be installed by clamping the holding ring down on the spring that holds the bearing in place. This shows the bearing with the spring:
After slightly bending the tabs of the holding ring,
I used my special tool with adjustable pliers to clamp the tabs fully down:
This ensures that the bearing is held in place snugly as it was before disassembling the motor.
Then I put the motor back together:
After soldering the PCB back on it was time for a test with my bench supply:
A properly assembled motor should draw less than 30mA at 5V. If the current is higher the brush career plate needs to be loosened and the screws carefully tightened in several small steps in sequence around the motor (as you would tighten a vacuum flange).
These motors are very sensitive to improper alignment of the shaft with the bearings and they will not run well if this is not done properly. Another frequently encountered issue is that the motor runs in the wrong direction after assembly (or it runs not at all). This is caused by the brush carrier plate being mounted at the wrong angle relative to the permanent magnets in the motor. If that happens remove the screws, rotate the bottom plate by 120deg and try again. If it still not works properly, do another 120 deg and then it should run int he right direction. Generally, it is a great idea to make an alignment mark with a Sharpie pen before taking the motor apart...;-).
Alright, it seems this motor is running well again...the grinding/screeching noise went away. I will give it a RPM test with my BeoloverRPM device after I rebuild the main PCB with a new RPM relay and RPM trimmers. These items are the other leading trouble spots causing unstable RPM performance of DC motor Beogram 4002s.