Beomaster 8000 (1903): Updating the LED Displays with a Roslinde Beomaster 8000 Display Kit

I am in the process of selling a Beomaster 8000 (Type 1903) that I restored a while ago. When I set it up for testing I realized that I did not replace the original LED displays back then. The reason was that this Beomaster did not have any missing display segments. Since I used it in my house I thought why not wait until the first segment would go out. But now I need to ship this unit and so I thought it prudent to replace the displays with modern LEDs. The original ones are pretty fragile at this point in time and frequently fail. I used to do this process manually by scratching off the original LEDs from the circuit boards and hand-soldering 0603 LEDs into their place (see here for an example of this approach). This process usually kept me busy for a few hours.

Annoyed by the thought of having to do all this microsurgery I got ready to get professionally manufactured display PCBs with surface mounted LEDs made. But then I was made aware that Roslinde Electronics in Denmark already had beat me to the task! They even designed similar PCBs fitting the Beomaster 6000 and the Beocord 8000-9000 displays! Very Beoawesome!

I ordered a set of the Beomaster 8000 PCBs. This is what I received:

In the kit were the four PCBs matching the four original LED displays of the Beomaster 8000. There were also board headers that needed to be soldered in place and bent to match the headers on the original boards. Since modern LEDs are a bit brighter than the 1980s types mounted on the original boards, there are also cut-to-size filter foils that reduce the intensity of the new LEDs to a level matching the output of the original ones. 

Let's see what needed to be done to install them:

The first step was extracting the display PCB from the Beomaster. If this is a mystery, have a look at the service manual that is widely available on line.

This shows the extracted board:

I unsoldered the top right display that shows the FM frequency:

This shows it from the side. Note the bent pin header that enables the display to be mounted at an angle relative to the board:

This shows the backside of the assembly:

The red and white 'thermo-squashed' plastic bumps hold the red display cover and the underlying light aperture in place:

For the removal of the red cover the squashed part of the bumps needed to be removed. I did that with a razor blade. This shows the red bumps liberated:

After removing the red cover the aperture piece that shapes the segment appearance is revealed:

After cutting off the white plastic bumps the aperture could be removed, too, which revealed the PCB with its non-encapsulated LEDs:

Installation of aperture piece and red cover on the new boards is straight forward. I elected using white wood glue for fastening the pieces into the mounting holes since I am a believer in 'reversible' modifications, i.e. modifications that can be again restored at a later point in time (think about this Beomaster being unearthed a second time in another 40-50 years with a new generation of Beolovers rebuilding it once again!...;-). I just put a bit of the glue into the mounting holes with a toothpick and then I pressed the aperture and cover into place. Then I secured everything with carpenter clamps on my bench top until the glue had hardened:

This shows the reassembled display:

After soldering in the headers and bending them with pliers to the approximate angle of the original boards I implanted the newly rebuilt frequency display in the Beomaster and fired it up: 

Way to bright, as expected! I just wanted to see the difference relative to the original displays before applying the provided filter foils. This shows the display after I put the filter on: 

An excellent result! The new display looks very similar to the original ones! Beoperfect! This encouraged me doing the remaining three display assemblies. Here you can see them clamped while the glue was drying:

This time I soldered and bent the headers before re-assembling the display units. Note that the balance display header has a different angle than the other three. Details, details!...;-). This shows all four rebuilt displays in place and illuminated:

Very nice! In summary, I can only recommend using Roslinde Display Kits for Beomaster and Beocord restorations! 

Beogram 4002 (5513): DC Platter Motor Not Spinning Anymore

I restored the PCBs, DC platter motor and RPM panel of a Beogram 4002 from a customer in California in January 2021. Recently he contacted me stating that the platter motor stopped spinning. I asked him to return the parts so I could have a look.

After I received them I implanted them in my bench 4002. Indeed the platter motor did not spin anymore! The culprit was found quickly after checking the motor voltage at the red wire of the motor harness. I only measured 2.4V. It should be around 9V if everything is o.k.

The motor voltage is stabilized by 1TR2, originally a TIP31 power transistor. Since the Zener diode still made ~10V, it was most likely the transistor. I replaced it with a stronger TIP41:

And everything was good again in the motor voltage department. 9.6V at the red lead!:

In 2021 I had not understood yet that the power transistors on these boards often have issues. Maybe age related, maybe just wear from years of playing records. Informed by repeat transistor failures that I encountered over the years, I now always replace them all when I restore a Beogram 400x. So I set out to update this board to my current state-of-the-art. It is best to replace the two power transistors mounted on the solder side of the board when the board is installed. It makes it easier to position them correctly that the mounting holes match up. This shows 1IC1, which regulates the 21V power rail. It is usually a TIP120:

I always try replacing power transistors with stronger types for enhanced longevity. In this case a TIP102 is a good choice:

For some reason modern TIP replacements need some capacitance at their emitter in this circuit configuration to prevent high frequency oscillations superimposed to their emitter output. That is why I soldered a 100nF cap (yellow-orange) between the emitter and a conveniently located GND solder point nearby in the above picture.

The second transistor on the solder side, 1IC4, is usually a TIP125, 

whose stronger cousin, the TIP107, makes a good replacement:

After this I removed the board and also replaced the often fail prone H-bridge transistors with new types. this shows the updated board with the extracted parts:

I installed the board again and successfully tested all functions. These parts are ready for duty again and will soon travel back home to their Beogram 4002 in California!

Beogram 8002: Repair of a Dead Display Digit

Another issue plaguing the Beogram 8002 that I am finishing up right now was that the fourth digit of the RPM display was dead. This shows the sorry state of affairs before my repair:

Since all segments of this digit were not working the most likely root cause of the issue was a missing strobe signal for this digit. A measurement with my oscilloscope at the strobe pin (14) on the display confirmed this hypothesis. Time to 'follow the signal', which is not the most straight forward thing to do in this setup since the unit must be running to do the measurements. I installed some micro-grabber leads in the microcontroller can at strategically important points and then did the measurements with the board installed. It turned out that the trace that connects processor pin 13 to the base of IC6 (the Darlington that drives digit 4) was interrupted midway (between the solder points of the white and ground leads):

The way this looked suggested that this was probably the result of 'human interaction', and of course one wonders what may have compelled anyone to poke around there with a sharp object causing the trace to come off. Anyway, I reestablished contact with a piece of magnet wire:

and the display digit came to life again:

Time to put the hood back on, do the mechanical adjustments and then do some 'reliability testing' (= listening to some awesome vinyls I recently bought...;-) on this lovely Beogram 8002.

Beogram 8000: A New Arrival and Restoration of the Control System

A Beogram 8000 in need of some TLC recently arrived. It had been purchased on ebay with two MMC20 CL cartridges...very nice!. Unfortunately, it did not work anymore upon arrival at its new owners location. So it traveled on to my place and here we are:

The unit has the usual fallen off aluminum panels. Luckily someone catched them before they hit the floor and they are unscathed. Overall this unit is in pretty good condition and all seems original (if there just weren't the tough layer of Gorilla glue on the hinge of the smaller aluminum panel):

I opened it up and found a slightly dusty interior, but nothing otherwise unusual:

Then I had a look under the sub-platter where I found a metal tacho disk:

This is great news since the original plastic disks tend to delaminate, which causes severe RPM instability.

So far so good. When I tried to run it the platter would not spin, and the carriage showed some reluctance to move. Nothing unusual at this point in time for a Beogram 8000 in original condition. When the platter has trouble moving, it usually has to do with bad power block connections or a dead motor phase capacitor.

I decided to go ahead and rebuild the electronics. This involves replacing all electrolytic capacitors with modern Japanese major brand 105C types and reflow all the board to wire headers solder points. They are often cracked and this causes intermittent operation of the deck. Here are a few impressions. This shows the main boards taken out:

Most of the capacitors are straight forward to replace. The one that is usually a bit of a pain is the processor power supply decoupling capacitor in the EMI can. I took the can off the board and opened it up:

The processor was stuck to the can lid and popped out of its socket...In those days these chips were quite expensive, and so they used sockets instead of soldering them in directly. For exchanging the capacitor a removed processor is perfect. So I left it stuck to the lid for now. The picture below shows the original 47uF capacitor in question. It makes the GND connection (left) on top and not on the bottom solder point, which are not connected by a through plated via like one would expect on modern boards. This can be confusing since failure to solder it to the top contact pad will cause erratic processor behavior. I once spent an entertaining evening with an 'exploration' of this issue...see here for a description of that Beolover adventure...;-).

Anyway, I exchanged it:

and then I removed the processor from the can lid and inserted it back into the socket and replaced the lid and mounted the can back to the board. This shows the recapped board with the removed original components placed next to it:

After that I reflowed the solder points of the headers. This is best done by adding a bit of solder to each point. The boards were soldered with relatively sparse solder application, which may be one of the reasons that so many Beogram 8000s have bad joints. Indeed, I found several cracked points, mostly on the main power block header. This shows the pins where the motor phase capacitor is connected:

Both have a telltale ring around the soldered pin. This probably explains why the platter behaved erratically. I resoldered everything and then it was time to put the board back in. The next step was the replacement of the motor phase capacitor that is located in the power block:

I usually replace this big can with two modern 47uF bipolar units back to back. This turns them into a single 23.5uF unipolar capacitor, which works perfectly. Since modern capacitors are much smaller I recently designed a 3D printed insert that holds the two caps neatly in place:

After reinstalling the power block I rebuilt the power supply board that is next to the sub-platter:

It has only two reservoir capacitors that need exchanging:

This concluded the restoration of the PCBs, and it was time to do the carriage servo control voltages adjustment to the prescribed 620mV (err on the smaller side if you must, this adjustment can be a bit sensitive):

And then it was time for a test! And as expected the Beogram fired up normally with the platter moving smoothly and the carriage looking for a record. All good in control system land! On to the mechanical parts of this lovely deck!

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...