Beocord 9000: Ready for Bench Testing

This weekend I completed the seven segment display rework. I didn't run into any problems with the LEDs during the twenty-four hour burn-in test. After re-assembly of the display I checked the LEDs again. My test jig has two sections for testing the Beocord display. The one shown on the left runs tests with every LED illuminated. The section on the right is when I want to check one LED channel at a time. Or I can check just one LED at a time if I move some jumpers.

During the individual display test I noticed there was a little bit of LED bleed through from the middle "dot" LEDs into the adjacent segments. This would be a noticeable thing when the Beocord is in standby mode.

I checked that all of the SMD LED components were centered in the light guide. The base of the guide was not resting on any part of the LED. Then I remembered this board has three trace repairs. The thin repair wire must be preventing a perfect mating of the light guide base to the board. To fix this I applied a thin coat of black automotive weatherstrip adhesive to the bottom (base) of the light guide. I made sure no adhesive could get into the LED slots. This was also a good thing because the three, white, plastic mounting pegs of the light guide had to be cut away to dis-assemble the display. This adhesive would now block bleed through light at the base as well as attach the light guide to the base. I apologize for not having any pictures of this step but the adhesive has too short of a working time to allow for stopping and taking photographs.

The result worked very well although the short work time of the adhesive made for some assembly stress on the repairman. To prevent any LED light bleed through anywhere else on the assembly I taped up the back as Beolover does on his display repairs. For the outer sides of the light guide though I added a coat of black 1-Shot enamel paint.

The final step was the mounting of the red display cap. I used black hot glue to secure the cap to the rest of the display.

Here is the result.

At the lower right of the picture above you can see the Beocord's lithium battery. That supplies offline power to save any cassette calibrations the user has stored in the Beocord. The battery is soldered to the board via a couple of solder tabs so it requires de-soldering and soldering to change. This battery measured okay but it is a good idea to change the battery install to use a battery holder. That makes changing the battery a much simpler job in the future and no worries about a battery explosion (when de-soldering).
Here is the reworked Beocord battery.

Now I can button up the Beocord and move it over to the test bench. I might still have some tweaks on the Beocord before I send it back to its owner but we'll see what comes up during testing.

This frees up my workbench so I can now start on the Beocord's master...as in Beomaster 8000. That will be the next step in this restoration work. I will do a quick check of the pre-restoration state of the electronics. Then I will start in on the work.

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.