Beomaster 8000: Display Board (part 3)

The plastic mounting tabs of the light guide and lens cover for the display modules were originally long enough so the ends could be melted. The melted ends of the mounting tabs flattened out to hold the light guide and lens cover to the display PCB. Obviously those flattened ends had to be cut in order to remove and replace the LEDs.

The reassembly of these LED display modules could just involve gluing the light guide and lens cover back in place. What we like to do is go a little bit further. In testing the displays we notice that LED illumination exits the back side of the display boards and could end up being visible from other areas of the display. To prevent that we wrap the display in black tape and use some black hot glue to help seal the module together.

Here is the balance display as an example.

That seals the display module pretty well I think. The same thing was repeated for the other three display modules.

Re-attaching the displays to their plastic holders and inserting the connection leads through the display board is a little difficult. It can take a surprising amount of manipulation (and time) to get the modules reinstalled on the board. 

Finally this one is done.

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.

Beomaster 8000: Display Board Rebuilt

The reworked Beomaster 8000 display modules have spent enough time on the test jig. All of the new SMD LEDs passed the burn-in test so I can finish up the last circuit board in this restoration project...the display board.

Here is the board with its original components. The arrows designate the board components that will be replaced: The four display modules, the four light bulbs, a 10uF electrolytic capacitor and a 4.7uF tantalum capacitor. The four light bulbs will be replaced with Beolover's direct replacement LED component. That means also removing four 220Ω resistors (R34, R36, R38 and R40). As with all of the other Beomaster 8000 board restoration, I reflow the solder on all of the board connectors.

Here are the lamps and resistors alongside the new Beolover indicator light modules.

Here we go, the last board re-installed in the Beomaster...and everything works. An expected result but always a relief to actually see.

Note that it is always difficult to get a good photograph of the LED displays the way they really look. If I turn down the ISO and shutter speed I can get a better representation of the displays but then everything else is too dark. The display segments all look uniform and will match the Beocord 9000 I did earlier.

This Beomaster is about ready to close back up for the bench, system testing phase. However, I do need to rebuild the lid damper before I can put this unit back together so it is time to start that repair.

Update: Here are some better photos of the new displays in the Beomaster. They look quite good I think. I followed Beolover's basic restoration method of blacking out any sources of stray light from the LED using various materials like black vinyl tape and black hot glue.

Beomaster 8000: Updating the Displays - Completed

Today I finished replacing a set of Beomaster 8000 display LEDs with SMD LEDs. This set had numerous faulty display segments so it was badly in need of repair.

I was a little disappointed that my SMD work station method of doing this task fell short of expectations. In my earlier restoration of the Beocord 9000 displays the work station method worked quite well and I felt like I only needed to perfect the process a little before it became my new way of doing these displays. Now I think that was just beginner's luck. Since that first display repair the SMD work station technique has meant a lot more rework and waste of new SMD LEDs (that had to be tossed when the installation failed).

The problem with the SMD work station is that even with minimal air flow, the SMD LEDs can shift during soldering. Even in the case where the solder pads are small I usually run into over half the LEDs not soldering in the position they need to be. With these Beosystem LED displays it is critical that the LEDs stay within a narrow range in their positioning. The reason for that is they have to fit nicely in the slots of the plastic housing that guides the light.

So after that hopeful experiment I have reverted to the tried and true manual soldering process.

To show what I am talking about here is the preparation for the Beomaster 8000 channel balance display. This picture shows the SMD LEDs in place on their solder paste ready for the heat to be applied.

After the board heater and heat gun melted the solder, the result was quite unsatisfactory.

The LEDs circled in red were not successful. I had to toss those LEDs as I don't trust them to be reused once I remove them. These SMD LED devices are pretty delicate so I don't want to risk them failing later on.

Here is the reworked board after manually repairing it with old fashioned tweezers and soldering iron. I used my de-soldering gun to clean up the excess solder.

Now that I decided to change over to the manual soldering method I prepared the next board by cleaning with alcohol and tinning the solder pads. This is the Beomaster 8000 volume level display.

Before placing the SMD LEDs I apply some solder flux with a syringe. The SMD board heater at least provides a nice way to hold the board in place while I work on it.

Here is the completed volume level display. As I did each display I was able to refer back to my photos I posted in the previous post that show the LED orientation on the pads. That was very helpful as I could just look at my smart phone for the reference photo as I placed and soldered these LEDs in place.

Next is the Beomaster 8000 function display. Here is the prepped board.

...and the finished board.

Finally the last board, the FM frequency display board. These display restorations are probably the most difficult job of the entire restoration. The work is very trying on one's patience as it is easy to get frustrated if you can't keep a steady hand. You have to be in the right frame of mind when doing this. 

Here is the last board before tinning. The marks between the pads is where I used a razor knife to cut the tiny pad the original LED mounted to. I found that trying to leave in place is risky because it is such a narrow gap. It is easy for solder to bridge that gap and cutting it out leaves a perfect gap for these SMD LED components.

Here is the board tinned and with solder flux in place on the pads.

The last board is now complete. One other note about the manual soldering process. I often just solder one side of the SMD LED to hold it, then test fit the light guide piece to make sure the LED component is centered in the slot. That is an extra step but it actually saves rework time and risk in destroying a good SMD LED. After I verified the fit I solder the other side of the LED.

Now it is time for the display burn-in test. I reworked my test jig since the last post and I am now going to leave these displays operating for 24 hours to make sure none of them are faulty.

Just for a reference I put the channel balance display completely back together (just pressed together, not permanent yet), the volume display and function display with just the light guide attached, and the FM frequency display bare. You can see the progression that the parts play in the final look of the display.

While these display modules are testing I can start work on the Beomaster display board recapping and the Microcomputer board recapping.

Beomaster 8000: Updating the Displays - Preparation

The next task on the list is updating the Beomaster 8000 displays. For the big, segment displays that means replacing the original Beomaster LEDs with modern, surface mount type LEDs. It would be great to be able to leave the original LEDs  (and sometimes an owner will do that), but eventually those LEDs fail. These units are thirty-five years old now. It is expensive to ship a Beomaster 8000 due to its size and weight plus it is a good idea to keep shipments (as in re-shipment) to a minimum. Lessen the chance of something bad happening in transit.

Here are the segment displays from some Beomaster 8000 units.

The first step is to get a test rig set up for these Beomaster displays. The work will be just like I did earlier on the Beocord 9000 display (...just more LEDs). You can setup a jig without load resistors and use the current limiting of the bench power supply but I want to set up my jig with individual control lines and load resistors like the Beomaster. I came close on this initial test set up but ran short of 68Ω and 82Ω resistors. I will have to add them to my next Mouser order which will probably be this week. Anyway, though not completely like I wanted, this test rig will allow me to check the reworked display boards. This picture shows the rig with a set of Beomaster 8000 displays that have all working LEDs.

Here are the individual Beomaster 8000 display pin mappings.

Now I am off replacing the LEDs with new SMD LEDs. Once that is complete I will use the test jig to run the displays for a few hours so I will know they are good. Then they will be assembled and re-installed in the display board. While the LED burn-in test is running I will be able to do the recapping of the display board and the microcomputer board.

Beomaster 8000 Display Issues

Today I looked into the display issue on Beomaster 8000 #4 (see http://beolover.blogspot.com/2013/09/beomaster-8000-first-inspection.html). The initial suspicion that there is something wrong with the communication between the microprocessors and the displays turned out to be wrong...the missing displays segments are just broken, like in most Beomaster 8000s when they come from ebay. I extracted the balance display and inserted it into my display test fixture and biased it with ~1.7V. Only four segments showed up for the party:

It is interesting to note that there are two 7 segment display decoders (IC1 and IC2 on the processor board (=#9)). IC1 addresses both balance and volume displays, while IC2 drives the frequency and the input displays. Which one of the two displays is on depends on the phase signal, which turns them on alternatingly at a frequency that is imperceptible by the human eye. It follows that the segment drivers are both o.k. if one of the two attached displays is showing a coherent data display (even with some display segments missing). The same is valid for the phase signals. Oh well: On to another display repair session (check out: http://beolover.blogspot.com/2012/09/beomaster-8000-display-repair-hopefully.html). I just ordered the SMD LEDs...for a consistent brightness across all four displays, I will have to do them all.

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!