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...

Beogram 4000: New Arrival from Italy

Exciting! Another Beogram 4000 found its way to my bench for a full restoration! TNT brought it over to the US in an amazing three days. I extracted it from the box. It was quite well packed and arrived safely. The exterior of the unit is pretty decent. No damages to the veneer and the hood is absolutely polishable:

The aluminum trim in the back of the hood came off on one side, but that can be fixed with double sided tape. After I opened it up and removed the aluminum plates (which are in dire need of a deep cleaning) I found that the carriage pulley had come off during transport:

Luckily the parts were easily found in the enclosure:

As usual the main key of the control pad extracted itself from the spring that holds it in place. This proves that it is absolutely necessary to tape the keys down for transport. I reinstalled the pad, switched the unit to 110V and plugged it in (keenly watching for potential smoke...;-). Nothing happened, so I pressed 'ON' and the carriage set itself into motion in search for a record. It stopped as expected at the set-down point for 12" vinyls. So far so good. However the solenoid did not engage. I moved the assembly a few times up and down by hand and then tried again, and there was a life sign. Very reluctantly the tone arm lift engaged after a tired motion of the solenoid plunger...

The unit came with the indication that the arm would not lower. It is clear that this unit needs a full clean and rebuild of the solenoid/arm mechanism. Also the solenoid looks strange and may be a non-B&O part. Other than that I found that the RPM switches are oxidized and do not work every time one presses them. The restoration will cure all that. On the good news end a working strobe light can be noted. 

In my opinion one of the intriguing features of the 4000. The position indicator, which is another remarkable design feature, was already broken once and glued back together. This indicates that this unit was in 'expert' hands at some point. The glue job is fairly well, done, though. 

Furthermore, the indicator light bulbs are dead. My SMD LED replacements will fix that for good. All in all I am pretty confident about this project. This Beogram 4000 is a good starting point for a full restoration, which will take it to near-new performance and looks.

Beomaster 8000: Display Restoration with SMD LEDs

After I replaced the indicator light bulbs of the Beomaster 8000 that I am restoring right now I did the 7-segment displays. The 7-segment displays are essential for the signature looks of the 8000 and dead segments are at best annoying. I usually recommend to rebuild the displays even if they are still o.k. since the death of individual segments is virtually unavoidable considering the age of the units and the potential rigors of shipping. The original LEDs in these displays are not encapsulated, i.e. the bonded contact wires are not protected against vibration and thermal challenges etc.... Therefore, the usual failure mode is loss of contact at the bonding locations. Final failure is often preceded by intermittence as these wire bonds. This Beomaster had a few segments in this stage, which may or may not explain the claim by the seller that the displays were in good working condition. I posted many entries in the past about my restoration process, a summary can be found on my dedicated Beomaster 8000 page. The pictures shown here are posted to document the work done on this particular Beomaster 8000.

This shows the display board after I extracted it:

This shows the displays after unsoldering them. It is mandatory to use a desolder gun for removing them to prevent damage to the fragile pre-FR4 age PCB:

Then I liberated the displays from their plastic mounts,

and opened them up:

Then I removed the original LEDs and then soldered SMD LEDs into place. Then it was time for my 24hrs test where I power the boards from a test-jig that I set up with a couple solders breadboards:

Then I put the covers back on and tested them again to make sure all segments survived the procedure:

Then it was time to solder the displays back in. Here you can see them mounted back on their plastic mounts:

And back on the PCB: 

And fired up together with the newly rebuilt indicator lights (unfortunately I forgot to use a FM preset, so the source display is dark in this picture). The volume is a 6.0 to get the clipping indicator to light up:

On to the uProcessor board.

Beomaster 8000: Replacing the Incandescent Indicator Light Bulbs with SMD LEDs

I always enjoy rebuilding the display board of Beomaster 8000s. So much of the signature looks of these units depends on the gorgeous large 7-segment displays and the masked indicator lights for clipping, filters, mono and manual tuning. With this particular unit I started out by replacing the indicator bulbs with my recently designed SMD LED based replacement boards. There are two versions of this board accommodating the two left and right incandescent bulb cabinets. The contact pads for the bulbs are mirrored in these compartments, while the polarity remains the same. This mirror symmetry requires different boards to accommodate polar devices like LEDs. Here is a picture of the boards that I installed:

When I developed these boards I made a video how to install them:

It is important to keep in mind that the LED boards run on a much smaller current than the light bulbs, and this requires the removal of the resistors R34/36/38 and 40 on the display board. Otherwise the LEDs will always be on.

This shows the original light bulbs in their cabinets:

And after replacement with the SMD LED boards:

And in on condition:

On to rebuilding the 7-segment displays.

Beomaster 8000: Left Channel Volume Cuts Out Above 2.9

Here we go again. My second Beomaster 8000 lived happy in the living room for about 8 months. We used it everyday, and it performed like new. After all, it had a full recap and restoration and also looks basically like new! Well, now it sat on the bench again. The issue: When cranking it up above 2.9 the left channel suddenly cut out, while the right one behaved normally. I swapped it out with BM8000 #1 and we partied on on that afternoon. It is like with classic cars: You need at least two if you want continuous service...;-). Today I opened it up. The problem was quickly identified:

The volume is digitally adjusted via a 6 bit attenuator made by Analog Devices. This AD7110 chip is able to attenuate the input signal in 1.5 dB steps based on a 6 bit digital input. This gives it 64 attenuation steps, which would amount to a total of 96 dB attenuation. However, the design of the chip assigned the highest four numbers (1111XX) to an infinite attenuation. With 000000 being fully open, this gives us an attenuation range of 88.5 dB in 59 steps. This explains the 0.0-6.0 volume scale of the Beomaster 8000. The beauty of this design is that the volume display directly correlates to the binary information sent to the chip. Each ±0.1 step corresponds to a ±1 change of the binary number sent to the chip. Form follows function!

Knowing the above, the fact that the volume cut out at 2.9 immediately suggests that the most significant bit (MSB) of the 6 bit data bus was not connected anymore. A glance on the circuit diagram of board 4 shows that pin 3 (the MSB) is pulled up with a 220 Ohm resistor to 5V. According to the circuit description this is a precaution to prevent the AD7110 from opening up fully if the data bus is disconnected. In this case MSB would be set to 1 through the resistor, effectively causing an attenuation of 48 dB, preventing potentially disastrous effects should a speaker be connected in this circumstance. I concluded that the MSB must have gone open circuit, resulting in a permanent MSB=1 setting due to the resistor. Hence, after passing from 2.9 to 3.0 the attenuation reverted back to 88.5 dB. In presence of the right channel blasting loudly, this appeared as a complete loss of the left channel. In fact, after disconnecting the right speaker, the volume on the left channel recovered to the 3.0-equivalent level when increasing the volume from 3.0 to 6.0, confirming the hypothesis.

The problem was easily fixed by cleaning the pin header contacts at the left channel AD7110. The location of the chip is shown here:

The two ribbon cables connect directly to the AD7110 for each channel. The right plug is next to the AD7110 regulating the left channel. This picture shows the chip and the 6 headers connected to the bus pins of the chip:

It is strange that the chip is not labeled AD7110, but rather AD13/002 8201. But the pinout seems to be exactly that of the AD7110. Anyway, after cleaning the pins of the header (I also bent them a bit alternatingly up and down to increase the tension in the female connector), everything was fine, and the Beomaster is back in the living room!
It is interesting to note that this chip was apparently $10 in 1981(see Analog Dialogue 14(2), pp. 7, 1980 - http://www.analog.com/library/analogdialogue/cd/vol14n2.pdf) if purchased in the "100s", i.e. a single chip would have run about $20. Adjusting for inflation this corresponds to maybe $50 in todays dollars. This helps explaining why these Beomasters were quite expensive back then (but also quite advanced for the time!).