Canada Beomaster 8000: Rebuilding the displays

I have the new smd LED components installed in the Beomaster 8000 segmented display boards and I am running a burn-in test on them.

It is a little difficult to capture (in a photo) what the rebuilt displays look like without the top lens cover on but the purpose of this test is to make sure all of the segments work. I usually run this burn-in test for twenty-four hours. That gives the new components a decent amount of time to fail if they are going to. I would hate to bundle everything up then have to disassemble the displays again.

To get to this point I removed the display modules from the Beomaster 8000 display board.

There are white and red tabs on the rear of the display board modules that hold the light guide and lens cover in place. Those tabs were originally part of the plastic sub-assemblies and melted down to secure the full display assembly. Since those cannot be removed and reused I have to just cut them off and use a different way to re-assemble the display modules after I rebuild them.

Here is the channel balance display board with the light guide and lens cover removed.

You can see these Bang & Olufsen display modules were very custom and the tiny, smd-like LED components cannot be replaced. We could locate the LEDs that have failed and just change those. However, that would result in a noticeable difference in the red illumination because the new smd LEDs are not exactly the same as the originals. They are very close but not the same. So it is best to change all of them. Another equally good reason to change all of the LEDs is because you can bet that if you only changed the failed LEDs the remaining good ones will likely fail as well. It's definitely better to get everything done while the Beomaster is open.

Here are some pictures from previous Beomaster 8000 display repairs that I use as a reference for this task.

This first picture shows the new smd LED component next to the original B&O LED.

This picture shows identifier markings on the replacement smd LED component for reference.

The next step in the display rebuild after removing the light guide and lens cover is to cut out the original LED component.

I gathered a number of my Bang & Olufsen display modules that I have been wanting to rebuild and hope I can take the opportunity, while I am display repair mode, to get them done as well.

To prepare each display board for the new smd LED components I cut off the small solder pad that the original LED cathode rested on. That makes the gap between the anode and cathode pads better for the new components.

It is important to "tin" the solder pads before mounting the smd LED components. That will ensure a good, reliable connection.

Now for the actual mounting of the new smd LED components.

I have to say that this task is one of the most time consuming restoration tasks and requires a lot of patience to handle the smd LED devices while soldering them in place. The technique I use (and recommend) is to mount the smd LED components just on one lead. The reason is because the LED component must fit just right in the plastic light guide of the display module. There are always several LED components that I have to reposition slightly to correctly function inside the light guide. That also means the soldering process is to first position the smd LED with tweezers, solder one side to secure it, check the fit with the light guide, reposition if necessary and finally, solder in the other side. Quite labor intensive and hard on the eyes.

Here is a fit check of the smd LED in the light guide.

Once all of the new LED components have been fit checked I finish soldering the LEDs to the board.

Here is the completed FM tuner frequency display board.

On to the remaining three modules.

Another tip is to have a reference picture or (even better) a spare display board to use as a reference when mounting the new LED components. This task is very tedious so be disciplined to check the polarity carefully with each LED mounting.  It is also another good reason to only solder one side initially.

Here is the completed LED replacement on the Beomaster 8000 selected source display board.
Note: The glare from my lighting off the no-clean flux residue makes a couple of the solder connects appear shorted.

The volume level display board is next.

Finally the channel balance display board. This board is the easiest to position the smd LED components on because it doesn't have pads where the LED mounts. However, the narrow trace makes soldering in the LED components a little tricky and this board is usually the one to have a connection problem.

Once the twenty-four hour burn-in test is complete I can reassemble the four display components and wrap up the display board. Then it will on to functional testing with this Beomaster.

Beomaster 8000: Repairing The LED Segmented Displays

The Beomaster 8000 has very distinctive, large, red LED segmented displays that are part of its modern design Bang & Olufsen created in the early eighties. The same type of displays were used in the Beomaster 8000, Beocord 800x & 9000 cassette decks as well as the Beomaster 6000 (225x).

Here is a Beomaster 8000 with restored displays.

Here is a Beomaster 8000 with original displays already starting to fail.

Now a picture of the display components removed and a view of the front and backs together.

After disassembly of the display modules here are the various pieces.

The next photos show the details of each display (balance, volume, source selection and FM frequency). The segment identifiers are shown as well as the display component connector information (+5V or Ground) to illuminate the LEDs.

As you can see the actual LED component is not a typical, discrete LED device from that era that was soldered onto a circuit board. These LED devices were manufactured special and attached to the board by some special process. An early form of surface mounted components?

Take a close look at the original LED device on the board.

Now look at the original LED device compared to its modern surface mount LED replacement.

The SMD replacement is like a nice packaged version of the original. A perfect replacement.

The mounting of the new SMD LED devices is critical. The construction of these B&O segmented displays is such that the LED must fit right in the small slots of the plastic light guides. The bottom of the light guide piece must press flat against the surface of the circuit board to block any light from illuminating adjacent segments.

This picture shows the display components better. The top left picture shows the slots the LED must fit completely inside of.

That precise positioning spoiled a plan I had to quickly install the replacement SMD LEDs using an SMD work station. I wanted to place the whole set of LED devices on the board in some SMD solder paste then use the work station hot air gun to perform the soldering all at once. As you can imagine some of the LED devices moved off line due to the air flow from the solder gun.

The tried and true technique is to solder each LED in place by hand using a two step process. After applying generous solder flux (I use no-clean flux) to the board solder pads followed by tinning the solder pads, I gently hold the LED down with a flat metal blade as I apply a dab of solder with my soldering iron (using a very small tip). I check the position of the LED with the light guide. If it is correctly in position I solder the other side of the LED and move on to the next one. Very tedious and labor intensive for sure but it works every time.

Here is a display board with the replacement LEDs soldered in place.

Now repeat that for the other displays. For the Beomaster 8000 that is sixty-five SMD LEDs to install.

There is also some preparation of the circuit boards before installing the SMD LEDs. Some of the original LED mounting pads are a little too close together for my liking to try and fit in the new LEDs.

Here are some photos from a Beocord 9000 display restoration I did that shows what I mean about the mounting pads.

Here are the pads after the original LED devices have been cut out.

The small tabs marked in red are the pieces I want to remove.

I use a razor blade to cut the original LED device from the board trace pads. I also use the razor to cut out the small trace tab shown by the red X above. You have to be very careful and steady while doing both steps. A slip of the razor and you have a broken trace to repair. Not a good scenario. However, with the removed tab the SMD LED fits much better. Perfect really.

Here is the Beomaster 8000 volume display board after the traces have been prepared (trimmed and tinned).

And here are the SMD LEDs soldered in place.

For reference, the SMD LEDs we use are Lumex SML LX06031W-TR devices.

After the display components have been retrofitted with the new SMD LED devices they need to be tested to make sure all of the LEDs illuminate. We use a home-made test jig to perform a 24 hour burn-in test of the displays before we go to all the trouble of sealing them up and re-installing them in the Beomaster.

I use a test jig where I have duplicated the Beomaster load resistors. I use a bench power supply for 5V power and ground.  Here are the displays being tested in various stages of assembly.

An optional step we do on our display restorations is to fully black-out the display component when we put everything back together. We found that by doing this we eliminate any stray light from the displays illuminating Beomaster areas that should be completely blacked out.

The sealing is necessary anyway as the original display components sealed together via a one-time-use plastic tab that was melted in place. To open the display for repair that plastic tab can only be cut off.

This display is now mechanically re-sealed and light beam sealed.

That is the whole process of restoring the display component.

Two other Bang & Olufsen audio components from this era share this LED segment display design. The Beomaster 6000 (225x) receiver and the Beocord 8000 - 8004, 9000 cassette decks.

At first look people (myself included) hoped that the displays are common and interchangeable. They are not. Here are some pictures of the displays from the various audio components side-by-side.

Even though the display segments for the display components above share the same look and number of LED segments, you can see that the mounting connectors are different and the control lines (on the rear trace side) of some of the boards are completely different. The only two that might actually be wired the same are the Beomaster 6000 and 8000 selected source display. But to try and swap those would mean a mechanical challenge of trying to get the connector leads attached properly.

The best thing to do if you have one of these components with faulty LED segments is to properly replace all of the display component LED devices with new SMD LED devices.

I hope this information is useful to other Bang & Olufsen Beomaster and Beocord owners out there.

Beomaster 8000: Display Board (part 2)

I completed installing the new SMD LEDs in the remaining three Beomaster 8000 display modules. It was pretty much the same as with the first display module except a lot more LEDs to solder. The job is quite tiring on the eyes.

If you are looking at refurbishing your own display modules I can tell you that the best method I have found is to solder one side of the SMD LED first, then check the fit of the display light guide. Last year I tried using an SMD work station that has a hot air gun and a board heater along with SMD solder paste. Unfortunately the solder pads on these display board are too wide and the hot air gun would blow the SMD LEDs out of alignment (but still on the solder pad).

The result was a lot of rework by hand so it is better to just do the LED soldering manually to begin with. One side first, a fit check and finally the other side. Tedious for sure but the displays work the first time this way.

I started with the largest display module, the FM channel display and worked my way down to the volume level display. Here is the FM channel display  beginning its testing.

Here are all four displays powered up on the test jig.

I will let them burn-in for twenty-four hours before I seal up the modules for re-installation on the Beomaster display board.

Once the displays are back on the display board it will be time to reassemble all of the refurbished boards in the Beomaster 8000 chassis and try this restored receiver out.