Beomaster 6000 (2253): First Contact and a New Volume Belt

A Beomaster 6000 (2253) arrived on my bench for some TLC. It came with an indication of 'the volume adjustment makes strange noises'. I opened it up and as expected I found a slack volume servo belt that was not able to drive the volume potentiometer all the way anymore due to slipping. This phenomenon was responsible for the noises when the potentiometer got stuck. I replaced the belt with an EPDM O-ring of the correct size and that restored the volume function. Here is an impression of the new belt installed:

While I tested the units other functions I noticed that the heat sink very quickly developed a pretty high temperature in the center area. This indicated that the right channel at least runs at a too high quiescent current. This is a common phenomenon in this generation of Beomasters due to the often corroded quiescent current adjustment trimmers. As they increase their resistance due to the formation of an oxide film the current gets ramped up. In the extreme this results in a burn out of the output transistors of the respective channel. This means this Beomaster should quickly receive modern multi-turn encapsulated trimmers for long-term stability.

Beogram 8002: First Contact, Exchanging the Electrolytic Capacitors and a Lesson About the Importance of Decoupling Capacitors for Microcontrollers

I recently obtained a Beogram 8002 in decent cosmetic condition. As usual, the aluminum panels had come loose, though:

After loosening the transport locks, decoupling the suspension springs, taking out the plate below the arms and removing the two screws that hold the top part of the enclosure to the bottom part on the left, I put the unit into service position. Then I plugged it in. Nothing. No red LED dot in the display and no response to any of the buttons. It appeared that, as is often the case with unadulterated Beogram 8002 (or 8000) that come out of storage, the reservoir capacitors of the power supply had gone bad. This usually prevents the processor from operating and that is the end of it.

I decided to replace all electrolytic capacitors and then do some more troubleshooting in case that would not fix the issue.

This shows the circuit board after removing it from the Beogram:

Here some details. This shows the reservoir capacitors of the power supplies:

I replaced all the electrolytic capacitors with quality Japanese 105C grade units:

There is one more big capacitor that needs replacing. It is located in the power transformer 'brick' that can be removed from the units and allows configuring them for different grid voltages. This shows the original 47uF unipolar capacitor (C1):

This capacitor acts as coupling capacitor for the two linear motor coils and gives them the desired phase shift. This is similar to the phase shift capacitor found in the AC motor Beogram 4002 and Beogram 4000 models which have run on two-phase motors. Probably due to the large size of 1980s unipolar capacitors this unit was put into the power brick. I replaced it with two modern bipolar 100uF units connected back to back in series:

Due to their small modern size it was necessary to design a fixture to hold them in place. I designed a 3D printed part that filled the vacant space in the power brick:

What was left after exchanging these capacitors were the two 5V voltage regulator capacitors soldered directly to the board that holds the 5V regulator and the +15V TIP32 transistor mounted to the bottom of the enclosure for heat transfer purposes. Unfortunately, I forgot to take pictures of these caps.

The final capacitor to exchange was the sole 47u electrolytic decoupling capacitor in the uProcessor can. It sits under the small board that holds the 4013 flipflop (IC7) that stores the tacho disk readout coming from the speed sensor (IC1) for evaluation by the microcontroller.

This shows the original capacitor after pulling up the flipflop board:

I replaced it with a new capacitor:

Note the solder point to the left of the capacitor where it is supposed to connect to GND. I forgot to solder it on the upper side, and that is where an interesting journey began that allowed me to 'explore' the 8000 and 8002 Beograms a bit more in depth...;-).

At this point I finally put the PCB back into the Beogram and then plugged it in. On the positive side it gave me a life sign on the display, indicating that power was restored. On the negative side the life sign was not a singular LED dot indicating readiness to operate, but it showed me "0.0.0.0." instead. Pressing buttons on the keypad yielded no response. Disappointing! 

I unplugged it and then plugged it back in and the display showed "1.1.1.1.". Very mysterious I thought! After a few more plugging in and outs it assumed the normal state and I was able to activate "Play". The arm started moving and everything seemed fine. Well, I repeated the plugging cycle one more time and I was back to "0.0.0.0.". At this point it dawned on me that the microcontroller had a hard time to start into its 'ground state' when power was connected, and that it rather entered a random state preventing it from executing its firmware. Since it seemed to occasionally end up in the proper state and then worked, I thought there was a problem with the controller itself. So I did an interesting experiment:

Since I only had one 8002 at hand but several 8000s, I extracted the uProcessor from a 8000 and plugged it into the 8002 instead of its original processor. The result was that nothing changed. Occasionally it would work but mostly not. I then replaced the entire 8002 processor can with the one from the 8000. And everything was normal! This is an interesting result by itself since it establishes that one can indeed run a 8002 with the processor of the 8000. Even the "<" and ">" arrows on the 8002 sensor arm work properly since they get their power via an analog circuit that depends on the direction of the carriage movement. There may still be some minor differences with regard to updated operational or control behaviors but basically the 8000 processor seems to have a very similar if not the same firmware on it.

This told me that the 8002 processor was o.k. but that it had a difficult time to reset during the establishment of the 5V power rail during power-up. I then figured out that by manually resetting the processor (via briefly connecting the junction between R74 and R76 to GND) after plugging the deck in, I was able to reliably start it up into the 'ground state' and after that everything seemed normal.

All this finally got me thinking about the power supply of the processor and I finally realized that the 47u coupling capacitor was not connected to GND due to the missing solder point on the component side, which is the only connection to GND of this capacitor. The bottom solder point is not connected, i.e. is only there for mechanical stability. 

I added some solder to the top point and then the deck worked (mostly) normally. The only issue I could see immediately was that the carriage moved at significantly different speeds in in- and out-directions. But this is the topic of another post...

Beogram 4002 (5513): Final Adjustments and a Test Drive with Freddie Hubbard's "The Love Connection"

My current Beogram 4002 (5513) restoration has come to an end. I did the final adjustments  I adjusted the platter height and did the sub-chassis alignment. 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).

Then I performed the arm lowering limit adjustment. There is another video on my youTube channel that shows how to adjust the lowering limits. This is an important adjustment to make since it can help protecting the cantilever in case of a record detection malfunction. The record detection circuit is not able to detect a light sensor failure by design and therefore if this issue should occur, and the deck is started without a record, the arm would be lowered on the platter (a painful thought!). That is the reason that the 'ribs' on the platter are designed with lowered sections where the arm would lower for the different record sizes.

Here is an impression of the effect of the lowering limit protecting the needle from touching the lower parts of the ribs:

Once the arm lowering limit is set, the tracking force can be calibrated. There is also a video about this process. This shows the tracking force gauge in action during the adjustment:

And then it was finally time for a test of this beautiful Beogram 4002! I selected a recent acquisition to my rapidly growing selection, Freddie Hubbard's "The Love Connection". In my opinion a great record. Unfortunately, it is widely derided for being too 'pop' and having too many pleasing melodies. Surely, it is not real jazz in a traditionalist interpretation of the genre, but it is absolutely great music. I even like Al Jarreau on "Little Sunflower" (I am not usually a fan of his own records). Check it out! Most of the tracks are on YouTube. This is the link to Little Sunflower. Now if they only had come up with a less tacky album cover...;-):

At any rate, this Beogram 4002 looked and sounded great while playing this album via the Soundsmith SMMC20 EN cartridge that came with it from ebay:

Time to send this beauty on to its new owner!

Beogram 4002 (5513): End Groove Detection Not Working

When I thought I was close to be done with this Beogram 4002 (5513), I set it up to play a first record on it. All went well until the side was through and the needle approached the end groove. The needle went all the way to the record label and then remained there playing an eternal "tk....tk.....tk....". Like in the old days with fully manual turntables...not very beolovely, though!

I removed the platter and had a look. I connected my oscilloscope to the collector of TR17, which translates the optosensor (4IC1) response from the position sensor into a 0-21V 'digital' signal that can be used to tell the control system where the carriage is located. The signal was all good for the major black bars on the position indicator, but was very weak for the run out groove area. This is usually a sign of a poor alignment of the IR diode relative to the light entry slit on 4IC1. The reason that the end groove marks are more critical in this regard is their small width. This creates a situation where a slight misalignment of the diode sends light into 4IC1 from the side, thereby 'muddying' the bright-dark sequence, which lessens the response of TR17. Another reason for end groove detection malfunction is an incorrect distance between position indicator bar and 4IC1. It needs to be pretty close to ensure that the narrow end groove bars really cover the light entry slit.

Anyway, I tried to reposition the IR diode a bit. This shows PCB 4 removed from the enclosure:

The IR diode is right in the center facing the black front of the sensor (this picture is actually from a different Beogram 4002 than the one that was fixed here...I forgot to take a picture before I repaired things).

When I tried to align the diode a bit better, it promptly broke in two:

I guess the old plastic got a bit brittle over the years...what now??

I tried replacing it with modern IR diodes that I had in stock, but to no avail. The circuit that drives the IR diode did not have a low enough impedance to drive the modern high output IR diodes that I had available. Even with 1R88 fully turned the voltage did not reach the prescribed 1.7V across the diode. I elected to not alter the circuit with a smaller resistor, but rather chose to use a classic red 5 mm LED, which had an appropriate low output and power consumption. This worked very well. Here you can see it implanted:

And in action:

Looks pretty, doesn't it? After this repair the end groove was detected nicely. It is interesting to note that the end groove issue probably was there for some time and omitted on the ebay description for this Beogram: It appears the previous owner tried to fix it by adding a thicker line to the end groove markings with a Sharpie pen:

The end groove markers are the narrow lines to the right. The Sharpie line is the wiggly hand drawn thicker line to the left of the narrow lines. The other lines on the left are the singles set-down marker (narrow) and the 45 RPM change marker (wide band).

It is interesting how they used different widths and the end groove lines-array to be able to elicit different and appropriate responses from the control system depending on the carriage position. Ah, the joys of analog control systems. Microcontrollers are so much more effective, but also much more boring...;-). This is Beolove!

Beogram 4002 (5513): Installation of New Gold Plated RCA Plugs

No Beogram 4002 restoration is complete without replacing the original DIN or RCA plugs. The original plugs are usually a bit corroded since they were not gold plated. It is a great idea to install modern all metal plugs with gold plated terminals. This increases protection against EMI interference and also ensured low contact resistance to let those small MMC20 signals travel to your amplifier unimpeded. This gives an impression of the original RCA plugs that were on the Beogram 4002 (5513) that I am restoring right now:

Pretty grim...I cut them off and installed nice Amphenol plugs with a full metal body and plated contacts:

And fully assembled:

Very nice! 

Unfortunately, this Beogram also had its grounding wire shortened:

What is it about cutting off cables?? A significant number of Beograms that found my bench in recent years had severed cables, either the power cord or the output cables. How about just curling them up into a neat coil and leaving them alone if they are too long?? Oh well, I replaced the cable fragment with a new pristine 16 gauge wire matching the RCA cables in length. All good again!

Beogram 4002 (5513): Oil Infusion of DC Platter Motor Bearings and RPM Test

A rebuild of the platter drive system of a DC motor Beogram 4002 is only complete if the motor bearings are relubricated. Most of the DC motor Beograms experience some form of intermittent RPM variations. The motor bearings are made from oil infused porous brass ("Oilite") and the oil in the pores runs out over time. These bearings can be 'refilled' under vacuum, which draws out the air so the pores can be replenished with oil. The difficulty with this process is mainly to get the bearings out of the motor without damaging other parts. I recently made a video that demonstrates this process in detail.

Here are a few impressions of the process while executed on the motor of the Beogram 4002 (5513) that I am restoring right now:

This is the motor extracted from the enclosure:

And after complete disassembly:

I changed my approach a little in recent restorations when it comes to taking out the bottom bearing. I now unsolder the feedback coils on the side that I lift up to extract the bearing:

I came to this conclusion after accidentally ripping off one too many of the flimsy wires that connect to the coils. they are extremely fragile, and the slightest stress will break them. Hence, it is a good idea to take one of the coils out that one can lift up the board to get the bearing out:

The next step was to infuse the bearings. For this I use a FoodSaver vacuum pump and a mason jar filled with SAE30 motor oil. This shows the bearings after pulling the vacuum. The air bubbles indicate air is leaving the bearing. 

After about 12 hours or so the process stops and the motor can be put back together. Then it was time for a test with my BeoloverRPM device:

The BeoloverRPM allows RPM logging over extended periods of time. Great for spotting intermittent issues. This graph shows the before and after restoration RPM curves over about 24 hrs:

The bottom curve was measured before the restoration and the top curve after. The negative spikes of the original curve show that the motor bearings had issues. After the oil infusion the spikes are gone. Happy listening! This is Beolove!

Beogram 4002 (5513): Installation of New 3D Printed Transport Lock Bushings

Before doing the platter and sub-chassis alignment adjustments I needed to replace the degraded transport lock bushings of the Beogram 4002 (5513) that I am restoring right now. It is important to have the bushings in place since the sub-chassis adjustment can only be done properly if they are in place. This Beogram was outfitted with the orange type of bushings,

which all seem to be in various states of degradation at this point in time. The gray looking bushings usually seem to be in much better condition. But these orange ones had to go. I removed the plates that hold the transport locks together, which revealed one of the brittle bushings:

I removed it,

And installed one of my custom designed 3D printed replacement bushings:

Each replacement bushing has two identical parts, so it can be installed by putting in one half from below

and the other half from the top:

Then the threaded rod and the top plate can be installed again:

There is a video about installing new transport lock bushings in my Beogram 4002 playlist. The replacement nylon bushings can be ordered directly from my Shapeways store. This is the link to the part. You would need two per transport lock.