Beomaster 8000: New uProcessor Crystals, Improved Decoupling of the uProcessors, and New IC Sockets

A Beomaster 8000 that I restored in 2014 recently returned to my bench due to some erratic behavior. Apparently it turns itself on spontaneously once in a while. While I was not able to reproduce this behavior for several weeks, I experienced it once with one of my own Beomaster 8000s, and there are some sporadic reports on the internet about similar issues.

Since I was not able to find anything wrong with this Beomaster, I am left with a hypothesis, namely that the uProcessor once in a while suffers from a power fluctuation or that one of the clock crystals is going bad, and that puts it into an unexpected state.

So I decided to replace the crystals and add 100nF decoupling capacitors to the power supply pins of the uProcessor IC, which only carry 1 uF from the factory. These days most of the time one finds 1nF in parallel with 100nF, which allows filtering a broader frequency range.

This shows the inside of the uProcessor can in original condition:

I removed the precious processor ICs from their sockets to ensure that they would not get damaged during the surgery. The crystals and also their capacitors can be charged with a high voltage out of the box, and that can damage the ICs. Therefore, I normally discharge all components against GND and I remove the ICs before working on this board. 

This shows one of the crystal setups in more detail:

I removed the crystal and their two 22pF oscillator capacitors and implanted modern crystals with their specified 18pF capacitors:

I also replaced the IC sockets, while I was in there:

This shows the an original and a new 2 MHz crystal in comparison:

When putting in the new 18pF capacitors, one needs to remember to solder one of the pins from both sides, since it serves as a via.

The final task was to add the 100nF capacitors. This is an easy thing to do since the 1uF cap is soldered between the 5V and GND pins on the back side of the PCB. This shows the original setup for IC3:

I simply soldered the 100uF cap in parallel across the 1uF cap:

After this step I put the board back in, and the Beomaster still worked...let's hope the new parts help suppressing the sudden-on phenomenon. Only the future will show...

Beomaster 8000: Step Six - Rebuilding the uProcessor Board

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ACHTUNG: Please, note that the crystal exchange procedure described here can damage the microprocessor chips on the uProcessor board. It is recommended to remove the chips before replacing the crystals and the capacitors. Due to the inherent capacitance of these devices, high voltages can be present between their terminals, which upon release, can burn out the gate that forms the oscillator together with the crystal. Make sure you short circuit the leads of the parts before installing them.

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After completing the display board rebuild with new SMD LEDs in the displays themselves, as well as replacing the incandescent light bulbs in the indicator cabinets with SMD LED based assemblies, it was time to do the uProcessor board.

The uProcessor PCB is the main source of operational trouble due to a few shortcomings in its design. In the 80s double sided PCBs were only beginning being standard in consumer electronics, and the earlier 8000s have boards without through plated vias. This made it necessary to insert metal plugs into the vias and solder them. Many 8000s have startup trouble due to these solder joints cracking. Luckily this Beomaster 8000 already had an updated board where the via plugs were replaced by soldered in colorful wire jumpers. This shows the processors, the jumpers and the crystals:

Another source of trouble are crystals that stop working reliably. This can cause severe malfunctions in the start-up circuit potentially damaging the main transformer. I started replacing them as a standard restoration item since I had a malfunction in one of my own Beomaster 8000s that caused the uninterruptible power supply (UPS) I run this Beomaster on to go in protection mode. This indicated that very high currents were flowing in the main transformer while the malfunction occurred. More here about this phenomenon. When the exact same condition happened in another Beomaster that I restored a few years ago, I took it as a sign that this is an issue that may be prevalent in many 8000s.

So here we go. This shows the old big crystals replaced with smaller modern 2MHz units. 

You can pretty much use any 2MHz crystal, as long as you also install the correct capacitors. The original crystals use 12pF capacitors to resonate, while modern units usually have 18-22pF. If you look closely, you will see that I also exchanged the two small capacitors directly underneath the crystals. They are now 18pF. 

I also replaced the two electrolytic capacitors on the board with high quality 105C grade Japanese units.

Here are some more photos: This is a detail shot of crystal X1

and a picture showing the solder side:

This shows the solder side of X2 for reference:

After this I plugged everything back together, and it was time for a test run! This shows the display board in all its glory:

Beautiful! Very Beolovely! By the way: One can 'provoke' the clipping light (left most) to come on, too, by setting the tuner to a station and then cranking up the volume. Above about 5.0 the clipping light usually comes on (make sure you do not have speakers connected during this test...;-).

On to replacing the speaker switches!

Beomaster 8000: Rebuilding the Power Supply Board and an Inspection of the uProcessor PCB

After the display PCB of the Beomaster 8000 was happy again, I focused on getting the basics on a sound footing. This means doing the processor board upgrade and a full recap of the power supply. So I started with the power supply PCB and replaced all electrolytic capacitors with 105C-grade capacitors from main Japanese manufacturers. Here are a few photos:

Power supply PCB extracted before recapping:

After recapping:

And installed:

After this was settled, I looked into the shielded microcontroller compartment to look into the B&O recommended upgrades. This is what I found:

It is obvious that this board came already with the jumper wires installed. These serve to bridge the often problematic vias, which are the main cause of operational inconstancies such as sudden stand-by or turn off of the output stages. Therefore, all I needed to do was to replace the two decoupling capacitors on this board. Here is a picture after putting the new caps in:

Next step is to open up the heat sink cover and replace the speaker switches and the four 10mF output reservoir capacitors...they seem to bulge a bit, a sure sign that they are about to go.

Beomaster 8000: Frequency Dial Not Working

Today one of my friends came over with his Beomaster 8000 in his arms...I restored this one a few years ago, so I felt responsible. The nice bottle of Napa cabernet that came with the Beomaster also helped...;-).

So I put it on the bench and opened it up. A quick test whether the infrared LED in the encoder is toast is by shining a flashlight into the encoder to temporarily 'replace' the LED. The IR receivers in the encoders are somewhat sensitive to white light, i.e. they work with a strong LED flashlight. If the encoder works with the flashlight, the LED is toast (see my entry about fixing these LEDs: http://beolover.blogspot.com/2012/07/beomaster-volume-encoder-repair.html)

In this case the flashlight did not do anything....so I checked the encoder outputs on plug P79. There I got the proper 5V square waves, i.e. the encoder was working.

The next step was to measure the signal at the Schmitt trigger (HEF40196B, 9IC7). The signal arrived there...so on to 9IC3, the master microcontroller. And bingo: no signal at pins 13 and 14. This meant that in both A/B signal paths from the encoder the vias died...

It occurred to me that back then when I fixed this Beomaster up, I did not yet routinely rework the vias on the microprocessor board (PCB #9) when restoring the 8000.
So, I re-soldered all the vias on the board (I assumed the others were probably also close to no-contact...), and everything was fine!

Beomaster 8000 Suddenly Cuts Output Stages Power

It has been some time that I had to post something noteworthy of my B&O efforts. I guess this means that all my Beos are in a happily restored state. However, like with classic cars, one needs at least two of each no matter how perfectly restored they are. This showed last night when we indulged in one of the new Longmire episodes and suddenly in the middle of the show the Beomaster 8000 output died. A quick on/off cycle indicated that the ramp up relays on the main transformer did not switch anymore: The Beomaster was quiet like a lamb, but still turned the display on and off in an orderly way. This suggested that there was an issue with the communication between the microcontrollers and the relays. I switched out the Beomaster with one of my other units and we continued watching.

Today I opened the Beomaster up. After plugging it in and turning it on, the relays clicked like never anything happened. An intermittent problem...don't we love them?? Well, on the other hand this suggested immediately that there was a simple contact issue somewhere in the path between the responsible microcontroller (IC4) and Relay 2 on board 7. I slightly bent the microcontroller board back and forth, and promptly the relays cut out again. I followed the path from the plug to the microcontroller with my multimeter (IC4 pin #16 should pull the line to the relays down to ground when the Beomaster 8000 is on). What I found was that the via that connects the trace from pin #16 through the board right above the pin of the microcontroller had become an intermittent contact. The photo shows the three vias (in the center of the pic between "9" and "C97"). Please, note that getting there requires removal of the bottom part of the shield can that limits the RF emissions from the processors - this can be done by carefully inserting a screw driver in various positions around the can and turning its blade, thereby prying the lid off without bending it.

I had a similar problem before with the first Beomaster 8000 I restored. That one would out of a sudden go into stand-by, and not wake up anymore. In that case the pin #14 via was the culprit. I think the lesson here is that a complete restoration of a Beomaster 8000 should include the preventive measure of resoldering these vias.

Fixing was quick: I put small dabs of flux paste on the vias and then simply heated them until liquid with my soldering iron (at 380C). This restored the Beomaster to its original reliability and it is now happily back in our living room.