Beomaster 8000: Display Board (part 1)

The last remaining board to work on is the display board. I guess I saved the easiest board to remove for the end. It only has two capacitors to replace so it should also be the easiest board to work on. However, the digital displays on this board often begin to have faulty LED segments after thirty five years. On the capacitor replacement we replace all of the electrolytic capacitors regardless if one still measures in spec. The reason for that is we know they can and likely will fail. The same reasoning goes for these displays.

Here is the display board for this Beomaster prior to the restoration.

I removed the four segmented display modules as those are the components with the LEDs that eventually start to fail.

There are also four incandescent bulbs (Clipping, Filters, Mono, Manual tuning) that will get replaced with Beolover LED replacement modules.

Here are the two electrolytic capacitors replaced (a 10uF and a 4.7uF).

Here are the before and after pictures of the incandescent lamp replacement.

Note that four 220Ω resistors (R34, R36, R38 and R40) are removed from the board.

The most time consuming task on this whole Beomaster 8000 project is the replacement of the LED displays. Since several Bang & Olufsen components from this early eighties time period use this type of display I made a test jig for bench testing them.

I always check whether any segments have started to fail or not.  It turns out all of the display segments are still functioning on this Beomaster.

Very nice and a key design element to these Beomaster units. However, we would really like to insure that this Beomaster doesn't have to come back to the shop in a year or two if these old display segments finally start to give out.

Changing out the original LEDs with modern SMD LEDs is a tedious task and I need to get back in the mode of working them so I will start with the smallest display module first...the channel balance display.

Here is that display with the red lens cover removed. You can see the tiny LED components in the display guide slots. Lining up the replacements in those slots is important.

Here is a further breakdown of the channel balance display. The display guide is now removed to better reveal the original LED components.

Those LED components are quite a challenge for eyes as old as mine. It's a good thing I have plenty of magnifying tools to help me.

Here is a closer look at the original LED component compared to its modern replacement.

For more detail on these displays you can check out an earlier Beolover Blog of a Beomaster 8000 project I did last year.

I soldered in three of the eleven new LEDs then did a quick test to check the work. So far so good.

After completing the replacement of the other eight LEDs on this lamp module I put it back on the jig for an overnight burn-in test.

The light guide fits perfectly over the new LEDs.

...and here is the lens cover snapped back on. After the burn-in test I will seal this module up better.

Three more display modules to go.

Beocord 9000: Seven Segment Display Board Reworked

It took a little longer than I expected to get my Beosystem display board rework station set up for doing repairs again but I finally got everything in place for repairing and testing the LED display. Here is my test setup for bench testing the display and running the burn-in test. I checked the setup with a working Beocord display.

Here is another look at the display board front and back. This time I have added markings for the segments and the polarities to follow.

There are thirty-one LEDs. This is what the original LED lights look like up close.

Here is the original LED compared next to the replacement SMD type LED.

To prepare the display board for the new SMD LED devices I will scrape off the old LEDs with a razor blade. I also discovered the new SMD LEDs solder in place better if the little pad the old LED rests on is removed.

That leaves the gap just right for the new LED device. Since I have quite a few Beosystem displays from this era waiting for repair I went ahead and ordered a reel of the replacement LEDs (Lumex SML-LX06031W-TR).

A little bit daunting when you first see how small those LEDs are. You must have magnifying equipment and SMD tweezers to work with these. Here is a picture of the Lumex SMD LEDs top and bottom.

I cannot see the cathode mark without the aid of a magnifying glass so I have to examine each one first as I pick it up with the tweezers. They are all oriented the same way in the reel packaging but I still double-check because I just want to make sure myself.

If you are just doing one display board then most people hold the SMD LED in place with tweezers and apply some solder with a soldering iron fitted with a small tip. I have done that before and it works well. However, I plan to do quite a few of these and with this Beocord display alone, that means sixty-two solder points.

Another option is to get an SMD rework station. I use an Aoyue SMD rework station.

The 853A is a heating system to preheat the board being soldered so you can lessen the amount of time the heat gun has to be applied to the board. I am currently using a temperature of around 180˚C.
After I let the board warm up, I use the 968A station heat gun at around 340˚C. I set the air flow on the heat gun to the minimum setting so none of the SMD components get moved out of position (by the heat gun air).

Here is the Beocord display board before and after processing with the heating station.

After that I cleaned the board with some isopropyl alcohol, examined with my magnifiers and checked continuity with a DMM. I found three bad board traces so I had to repair them with some thin magnet wire.
Finally, a successful board test.

I am going to leave the display board powered up in the test rig overnight to make sure everything is good. Tomorrow the display should be ready for full re-assembly and put back in the Beocord.
That will leave just a couple small tasks to do on this project and this Beocord will be done.

Beomaster 8000 Display Repair

Another Beomaster 8000 display repair marathon. I must have soldered about 280 SMD LEDs by now into these displays (it takes about 70 LEDs and this is my fourth display...;-). I basically repeated what I described in: http://beolover.blogspot.com/2012/09/beomaster-8000-display-repair-hopefully.html
Here is a pic of the outcome. I put them into my display test breadboards and ran them at 2V (~0.53 Amp):

All segments are present. It is a good idea to do a mechanical test while the LEDs are out in the open. I give them a pretty good push and pull with a toothpick in all directions to make sure they have good contact. Since there is no solder mask the solder has a tendency to distribute on the pads, and it can be difficult to create a decent solder bump at the contact pads. Inspection with a magnifying glass is also a good idea to make sure they are aligned and centered precisely. If they are not it is difficult to get the bezels back on in a way that they block the light laterally (if the bezels are not set well and there are gaps, then light enters adjacent segments and in a dark room this can be seen...not acceptable for the beolover!). Now I will give them a 'burn in' over night and then mount the covers back on. this Beomaster 8000 is hopefully soon ready for a test in the living room!

Beomaster 8000 Display Repair - The (Hopefully...;-) Final Solution

I finally had some time to get back to the Beomaster 8000. All that was left is to rebuild the display boards with SMD LEDs and to fix the keyboard (the TP2 button only worked intermittently, and that is the important button in the days of the iPhone as it allows to select the only input not used for its magnificent siblings, the Beocord 9000 and the Beogram 8000). Anyway, here a few pictures from my latest display repair process. I posted several times about displays in recent months, and if you care to pull them up, you can clearly see my progress in this matter. Here now, what I finally consider an acceptable solution to this fairly tricky issue with these units:

I used the same process to remove the red covers and white 'light conduits' (for lack of a better word) that I discussed earlier (I basically cut off the small plastic discs at the bottom of the PCBs with a scalpel, which immediately allows to remove the covers). Here a picture of the frequency display board after scraping the old LEDs off:

This picture shows the input selector board. Compared to the first two Beomaster 8000s that I refurbished this one shows a soldermask (green). Another 'advance' of this board generation is that the solder pads are now coated with another metal. Unfortunately, this metal coating did not survive the test of time too well, and it flaked off in several places when I removed the old LEDs. This is shown in the detail shot below.

I scraped the flaking parts off as good as possible to create a stable surface to attach the SMD LEDs to.

Here some pictures of the boards with soldered LEDs:

Nothing really new here, except that practicing improves skill...;-). I used MG Chemicals No Clean Flux Paste (8341-10ML) and standard Kester .4 mm solder wire (SN63PB37 #66/44). While it says "no clean" these boards defintely should be cleaned from residue in an Ethanol bath.

Now to the assembly process. This is the part of the process that did not satisfy me when I refurbished the first two Beomaster 8000s. Since there is no other way to get into the displays than to cut off the plastic discs that hold the red covers in place, the reverse process needs to inadvertently involve some kind of glue. Since I wanted to be sure that I could open the displays another time in case some of my solder joints would fail etc...I previously elected to attach the covers with Scotch tape. However, this did not look pretty enough in my opinion.

Another issue is that the 'light conduits' need to sit tightly on the PCB to eliminate optical crosstalk between individual LEDs. This is especially annoying when the Beomaster is off in a dark room. In this situation the single lit standby LED has a halo in the adjacent LED segments if the light conduit is not attached perfectly (o.k. I admit here that this type of concern is a sign of a severe B&O addiction, but what can one do??)

Here is what I cam up with for this set of displays:

This picture shows the light conduit of the volume display in place with a skirt of 5% window tint foil applied to stop light emission into the display-surrounding space

Seating the red cover squeezes the foil into place forming a tight light seal around the display block:

The last part of the process is to somehow fix the cover in place. Instead of taping it, this time I put dabs of super glue gel on the tabs of the covers where they emerge on the bottom side of the PCB. Then I put small squares of transparency foil on these glue areas. this has the effect that the glue is squeezed a bit into the surrounding space, similar to the plastic discs that I had to cut off to remove the covers. This is shown here:

Once assembled I pressed the entire thing together between two thick cardboard pieces using two carpenter's clamps as shown here:

After about 2 hours I removed the clamps and the displays were ready. Here some shots when I ran them on the breadboard set-up for a final test before reinstalling them in the Beomaster 8000:

Note the absolute darkness around the displays...no more halos. I should add that I also blackened the backs of the PCBs to stop light emission there, too.

After testing for 24 hrs I reinstalled the displays in the Beomaster. Before reinstallation I adjusted the display voltage to reduce the intensity to a level similar to the original displays like I described earlier here: 

http://beolover.blogspot.com/2012/05/beomaster-8000-display-brightness.html

This is a nice and fast method to get the intensity right without having to change all the current limiting resistors of the LEDs. 

On to the keyboard!