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By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Wednesday, October 19, 2011

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.

Sunday, October 16, 2011

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.

Sunday, October 9, 2011

Beomaster 6000 Display Repair - Pain and Suffering!

****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 guess I was too happy too early with my Beomaster 6000 display repair...While the LEDs survived my 12 hrs stress test under full load, they did not survive putting the apertures and lenses back on...two solder joints failed. I realized that the low temperature soldering paste did not work very well...after watching a few more SMD soldering tutorials by Norman Meir (yes, I am a fan!!) on youtube it became clear to me that I had to re-solder all of them. I doused everything in rosin flux and re-soldered with a fine tip at 340C using standard 60/40 solder (sparingly). It turns out that one needs to put the tip on the pad for about 5 sec to heat the part high enough that the solder actually flows on the contact pads of the LED. I tried not to touch the LEDs directly to avoid damage. This seemed to work fairly nicely. After wiping the board with alcohol it looked like that:

I tested each LED with a toothpick for mechanical stability. They seem to hold quite a bit of force without damage now...I hooked them up again to my connection manifold and turned them on:
We will see tomorrow, if they survived this torture. I must have heated each of them up about 10 times by now...

Saturday, October 8, 2011

Beomaster 6000 Display Repair

****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 glad to report that I was able to replace all LEDs in the frequency display of my Beomaster 6000, which also had a dead segment. I decided to give my Beomaster 8000 some rest, and try my skills first at the BM 6000, which is, I have to say, not as dear to my heart than the 8000. This pic shows the display with missing digit 2e:

Here is the display in disassembled state (just cut the red and white circles on the backside of the display with a razor blade. Be careful to not destroy the traces on the PCB when you do this!

This pic shows the red diffusor removed. The next picture shows the board without the aperture:

This pic shows the old LEDs as close as I was able to go with my camera:


I ordered some 14 mcd SMD LEDs from Newark.com (Lumex SML-LX0603IW-TR). These LEDs have a turn on voltage of 2V and run 20mA. With a razor blade I scraped the dead LED from its pad on the 2e location. Then I soldered one of the new LEDs in that location. This was surprisingly easy: I put some solder paste on one of the pads with a tooth pick. Then I held the LED with precision tweezers in the right location and touched the pad briefly with the soldering iron tip (which was at only 200C - I used the low temperature paste). Then I put some paste on the other side and touched the pad again. This was it. This picture shows the display with this LED inserted under standard operation condition inside the Beomaster 6000:

Works, but is way too bright...not satisfactory! I ordered some more LEDs with 9 mcd and 2.8 mcd output. I replaced some of the other LEDs with one of each of them - unfortunately pretty much the same result. It turns out that the 2.8 mcd LED was the brightest due to its lower turn on voltage of 1.8 V...It seems the old LEDs have a higher turn on voltage than all of the new ones. The next step was to try to change the resistors. Indeed the 14 mcd LED had a similar brightness after adding a 220R resistor in series with the already present 68R resistor for the e digits. I chose to not remove the old resistor since its second lead is soldered right underneath the volume indicator plastic foil, which is quite flimsy. I did not want another disaster to happen. It is probably difficult to replace the volume indicator...Here is the pic with the 220R resistor in place:
In case you wondered: The paper clip at R24 is in there to play with the other segments in digit 3 and 4 with the lesser mcd LEDs inserted at the c locations...these are off in this picture since no resistor is connected.
I decided to go ahead and replace all of the LEDs with 14 mcd ones. Here is the display board with the new LEDs:

I made a custom connector for the pins of the display board with some female header pins to run all the LEDs for 12 hrs at full output to test if they made it o.k. through the soldering process (three died right when I soldered them, but at that point I still used 280C-after lowering to 200C none died anymore). Here is a pic of the display under full output at 2V...A beautiful sight!:


Let's see if they will still be running tomorrow...






Sunday, October 2, 2011

Beomaster 8000 Speaker Switch Repair

I guess I was happy too early. Two days after putting the beomaster 8000 back together, out of a sudden the left channel cut out...Headphones still worked properly, so I immediately suspected the speaker switch. I plugged the speakers into the #2 outlets...still nothing on the left channel. Strange! Both switches broken? I never tried the secondary outlets, though...maybe the #2 switch was already broken...

I opened the Beomaster up again and checked...indeed both speaker switches dead on the left channel. I tried to find exact replacements, but of course drew blanks wherever I looked. I finally settled on model S201031MS02Q made by C&K. I ordered them from Mouser.com (Mouser#: 611-S201031MS02Q). These switches have a very similar sliding knob like the knob attachments of the old switches. They also travel 4 mm, identical to the old ones. This is important that they fit into the slots of the heat sink cover. But of course these new switches are lacking the PCB base of the original switches, i.e. do not fit into the slots in the Beomaster 8000 chassis. The pictures show one of the original switches (with the knob attachment removed)





This picture shows the PCB base plate removed from one of the old switches:

I modified the base plates with a Dremel tool until the new switches would fit on there exactly centered

The next step was to glue the plates onto the new switches. I used superglue gel and secured the plates with two grip pliers:



The modified switches were exactly the same height as the old ones with their knob attachments in place, i.e. the heat sink cover fit perfectly on top, and held them snugly in place like the old ones. I put everything back together only to realize that another display segment died...time to get back to SMD LED soldering practice...;-)