Beomaster 6000 Heat Sink Temperature

I recently fixed the output stage of a Beomaster 6000 and adjusted the quiet current to specifications. I thought it would be interesting to know what the corresponding heat sink temperatures are for future diagnostic purposes. Here is what I measured with a digital IR thermometer on the top of the 'cooling tower' in the back of the BM6000:

After ~1 hr of listening to the radio (volume set to 10) the right half of the cooling tower measured about 42-44C, while the left half measured 38-40C. The reason for this difference is that the right side houses the power supply, i.e. more heat is dissipated there. I expect that these numbers vary depending on the ambient temperature of the location. When I measured, it was about 20C.
If the BM6000 delivers temperatures significantly higher than the above values, I would think that the quiet current needs some adjustment.

Beomaster 8000 Display Repair Marathon

****note: This post is 'historic'...Please, visit this page for my latest display repair procedure: http://beolover.blogspot.com/2012/09/beomaster-8000-display-repair-hopefully.html****


I am on a roll!!! Today, I did the displays of my second Beomaster 8000 in one setting. Desoldering all the displays at once, opening them up, putting the SMD LEDs in...it took a few hours, but they look very nice. My best result so far...I guess practice pays off...;-).

I made one further change to the procedure: I used "No Clean Flux Paste" from MG Chemicals. I realized that paste does not evaporate as quickly as the liquid flux does. This makes it possible to put flux on all locations at once and then put the SMD LEDs on in one setting. It is recommended to do them in sequence by orientation, i.e. do all vertical ones in one setting, then the horizontal ones. This speeds the process up considerably. Also reliability increases. This time I had no failed LEDs. They all withstood the toothpick stress test (yes, not only European banks get this test...;-). The "No Clean" aspect of the paste did not work. I probably put too much on there. Therefore, I washed the boards in ethanol with a toothbrush. This worked very nicely. Here some pics of the completed boards:

I like doing the balance display best now. I realized that the smaller pads in combination with the green solder mask stops the solder from spreading.  This makes it much more straight forward to get enough solder on the contact pads of the LEDs. It also prevents the solder from obstructing the bezel, which fits perfectly after the refurb without the need for Dremeling the slits to allow for the solder thickness...These pics show the balance display board:

Beomaster 8000 Display Brightness Adjustment for New LEDs

This post describes what I did to adjust the brightness of my refurbished beomaster 8000 display units (see previous posts) to the brightness of the original displays (as compared side-by-side with my second 8000):

After studying the circuit diagram for the display PCB (#8) I tried to adjust the brightness of the display with trimmer R15. Unfortunately, even fully turning it down only reduces the display voltage from the originally prescribed 5V to about 4.5V (measured at TP 14). This did reduce the brightness a little, but by far not enough.

This led me to change R14 from 4.7k to 3.3k, and R16 to 1.5k. This pushed the voltage range of R15 down to about 3.6V-4.7V, while keeping the voltage divider intact (to not affect the "reset" circuit). Consequently, the supply voltage for the LEDs also dropped. This allowed a significant reduction of  the brightness. Adjusting the display voltage to 3.85V yielded a brightness similar to the original displays (maybe a bit higher, but I always felt the original displays are a bit low for daylight situations, i.e I decided to leave it at that; if desired the new voltage divider allows to go considerably lower with the intensity, but care needs to be taken to avoid dropping the keyboard strobe below ~2.7V). Here is a cutout from Diagram 3 from the service manual showing the discussed components:

It is interesting to note that R14/R15/R16 also control the strobe voltage for the keypad (measured across R24,27 or 30). Accordingly, my 3.85V setting at TP14 reduced the keypad strobe pulses to ~3.12V (from an original 4.2V). Here is a screen shot from my oscilloscope (after modification):

It turns out that this new lower voltage does not cause any trouble. The reason for this is that the 6500 microcontroller is based on TTL logic. TTL logic accepts HIGH signals down to 2.7V. Turning R15 fully low pulls the strobe below 2V, and the keyboard consequently stops working. This demonstrates that there is enough safety margin if the strobe is at 3.12V, i.e. no further modifications are necessary.

Beomaster 8000 Display Restoration

It has been a while...I finally had some time to take on the display of my first  Beomaster 8000. Some segments were out and this had to be done.

I used the same soldering approach like with my Beomaster 6000 displays. Dry tack per Norman Mier and then a quick soldering at 340C with regular leaded solder after dousing the tacked LEDs (I used again the LUMEX SML-LX0603IW-TR model with 14 MCD) with no-residue liquid flux (Kester #951). The most significant difference to the BM6000 experience is that one has to take out the entire 3-display bar at once. This is not possible without using of a professional desoldering pump (I use a Hakko 808). Serious damage to the fragile boards could occur if one tried to do this with de-solder braid or a spring loaded pump. 

The volume, program selector and frequency displays are very similar to the Beomaster 6000 displays. This picture shows them after repair during the test run. A test run is highly recommended. In fact, it is a good idea to run them without the diffusors on and test them for mechanical stability. I did this with a toothpick. I pushed them relatively hard on all four sides. Indeed a couple of the 54 LEDs flickered during this test and had to be replaced. It appeared that these two were damaged during the soldering process (the plastic cap wiggled on the metal base - I guess they got a bit too hot). 

Another thing I did different was that I did not use the brightness-reducing window tint foils to adjust their luminance to the original spec. I rather modified the display board enabling a proper reduction of their current to achieve the right intensity. More about that later.

The balance display is differently constructed. The tracks are much thinner and there is less space for the new LEDs. This means that one needs to be pretty accurate with the positioning of the new LEDs to avoid having to significantly Dremel the bezels out to make room for misplaced SMD LEDs. This picture shows the balance display after disassembly with the original LEDs.

These two pics show the display after repair:

And here the final result after adjusting the brightness. I will report about this process in the next posting.

Beomaster 6000 Display Repair - The Final Solution!

It took me a while to get back to my Beomaster 6000 displays. I was still not happy with the safmat filter. The brightness was not perfect. Also due to the laser printer resolution, the intensity distribution was not the same as before. The reason, it appears, is that the filter so created is not homogeneous, but rather black spots surrounded by fully transparent areas. This seems to result in a noticeably brighter center in each display segment than in the original ones. this may also have to do with the potentially more directed emission angle of the modern SMDs...
It occurred to me that I needed a color-neutral filter that is homogeneous on a as thin as possible foil. Some hard thinking yielded the idea to use automotive window tint. This material is completely homogeneous, and, a great plus, it is available in a variety of absorption coefficients. I bought a roll of "WINDOW TINTING FILM 50%" on ebay from a seller named "jollefemme" (after testing some darker tints from a local shop which did not do it for me), and it turned out that this worked perfectly. The additional benefit is that this material is also thinner than the safmat foils, i.e. fits more snugly on the LEDs.
To kill the light coming through the back of the PCB I put a sheet of 95% tint on the back. The pics show the difference between front and back filters:

I also changed the re-assembly method to minimize the light that would come from the crack between red cover and the PCB. It turns out that the window screen film is soft and pliable enough, that a few days of pressure applied with a couple of carpenter clamps practically eliminated the cracks altogether, creating a situation nearly as good as the original. Here a pic of the clamped display (I put it between two flat surfaces to avoid damage to the surfaces):

After a few days I took the clamps off, and secured the red cover in place with some Scotch tape around the non-contact sides. This worked very well.

After installation, I was hardly able to see a brightness difference between by still original Beomaster 8000 displays and the refurbished 6000 ones. Finally done! On to the 8000 displays...;-).

Beomaster 6000 Display Repair - Intensity Adjustment

After refurbing the TP8 display of my Beomaster 6000 I had another idea how to adjust the brightness of the new LEDs to the dim glow of the old ones. I did not like the 'halo' around the assembled displays coming from the small crack between the aperture plate and the PCB of the displays. Furthermore, the new (brighter) LEDs actually created quite a bit of light intensity behind the displays through the PCB. This caused a slight glow behind the displays even with the black cover 'bezel' mounted on top of the displays. I remembered that I had some "Safmat" laser printable foil. This foil is very thin and flexible, much more so than a standard transparency. It is also adhesive.

The idea was to put the grey filter right on top of the LEDs and not on top of the aperture plate. I printed one for the foils with the same "75% black" that I used for the transparency based filter (see last blog entry). Then I cut a strip a bit wider than the PCB, and of about twice the length and adhered it to the display:

Then I cut Safmat foil and wrapped it around the back:

Now I wrapped the remaining part also around the back:

Then I poked holes into the Safmat film where the mask and red filter positioning pins needed to be inserted into the PCB. These holes were small, with the idea being that the remaining material in the holes would help hold the mask and filter in place with a press fit. This worked fairly well, but I also secured the red filter with Scotch adhesive tape on three sides. This seems to do the job quite well. I did not want to use epoxy or similar since I wanted to be able to take things apart in the future if need be...here is the result:

Note that with the Safmat approach the segments are visible as they were before, even if the display is off...The transparency filter on top of the mask obscured the segments, i.e. the displays were not visible without illumination. Maybe that is more perfect, but certainly not original. Here is the display fired up:

Quite nice! the intensity is very close to the original LEDs. No crosstalk around the segments either-another advantage of the Safmat filter approach, since it covers the LEDs on all sides, i.e. they cannot shine light into adjacent segments.

Here is a pic of the installed TP8 display (sorry for the jitter-the camera was a bit slow due to the low light level). Note the halo around the frequency display-it still has the "transparency based filter" on top of the mask instead of the Safmat filter. The TP8 display in contrast is completely dark around except for the segments.

A note with regard to installing the cover bezel: The displays need to fit perfectly into the black clamps of the bezel. It took me a few approaches to get the angle and orientation of the displays right. After this experience it dawned on me that the better way would have been to just tack the displays on on the left and right most pins. Then adjust the angle and position as good as possible according to the marks that were hopefully made before taking them out. Now put in the bezel, and see if the displays fit in there. If not, adjust them by heating the two solder joints and moving the display into a better position while the solder is soft. Once the bezel fits smoothly, solder the remaining pins into place.

Beomaster 6000 Display Repair - Practice Does It!

I decided that I also needed to put new LEDs into the input/program selector display of my Beomaster 6000 to make both displays appear exactly the same. There is a very slight color difference between the old and the new SMD LEDs...the new ones are very slightly more orange...I am thinking one could probably fix this by using a bluish filter instead of the gray one I put into the frequency display...well, something for the next days. Now on to replacing the LEDs:

After removing the display and opening it up, I scraped the old LEDs out with a scalpel. This works very well. If it is moved parallel to the pads, it is virtually impossible to damage them. Then I studied a few more SMD soldering videos by Norman Mier on You Tube. I used his "dry tack" method to first fix the LEDs in place. To do this one first places a generous amount of rosin on the pads. Then grab the LED with precision tweezers and put it in an aligned location between the pads. Then take a very small amount of solder with the iron tip and briefly touch one side of the LED. After doing this with all of the LEDs, I then did Norman's "put solder wire halfway across the SMD tab to be soldered, and move the tip quickly in from the outside towards the pad". I held the tip for about 0.5 sec in place touching the LED to ensure good solder flow and bonding. The temperature of the iron was set to 340C. Here are a couple of pics of the result-much nicer than the mess I generated with the frequency display:

Even if some of the LED pads appear to be not coated by solder on the pic, they are. It seems that the pads usually only get a fairly thin coating during this soldering process. I tested the LEDs for mechanical stability with a tooth pick, and I was not able to damage the bonds even with quite some force.

Here is a picture of the display running. I plugged the pins into the female plug of an old parallel computer cable. The female plug at the other end of the cable was then connected to a breadboard's pos and neg rails with individual breadboard jumpers.