Gerhard:

Let us know how you make out and please!.. more photos.

Since you will be using SMT LEDs let me offer one additional piece of advice that has worked well for me.

Sometimes it is difficult to solder the SMT directly onto the pads because the copper has oxidized thus you should "tin" the copper surface first.

What you can do is to first apply solder to the pad to and then use a desoldering braid to soak up the solder so that you have a flat surface again. I find do this gives you much more even solder flow and makes soldering to the LED faster require less heat. It also looks nicer.

Derek

I have finally completed the LED display fix.  I tried several different SMD LEDs.  I started with 2.1mm X .6mm, 1.95v, 250mcd.  These were so bright I quickly discounted them.  I replaced them with 1mm X .5mm, 1.95v, 150mcd.  These were also too bright.  My goal was to find the closest matching LEDs without having to replace all the corresponding resistors too.

The final LEDs I used were 1.6mm X .8mm (0603 size), 2v, 14mcd.  I used these to replace all of the LEDs on the volume and balance displays.  As you can see from the pictures they are so closely matched you can barely tell the difference.  They are "diffused" lenses so you do not see a hot spot where the LED chip is.  Because of the low voltage and low mcd I was able to replace all of the LEDs without replacing any resistors.  Their size (1.6mm X .8mm) also made it easier to replace using a 1mm soldering iron tip and not have to use a hot air rework station.  To make it easier to see the parts I used a magnifying visor.  If your eyes are better than mine you could probably do with out that.  After soldering each LED I tested it with a work bench power supply set to 1.7 vdc.  That voltage is low enough to power the LED without a resistor.  I saved myself a lot of trouble by testing the LEDs before I assembled everything.  You will notice the board looks scratched.  I used a very small wire brush to scrape off the residue left from the original LED chips.

I decided to take the project one step further and added a header strip and socket strip to the display boards making them easier to insert and remove.

I order all of my parts from Digi-Key in the US (DigiKey.com).  They are fast shippers and have a great return policy.  Here are the part numbers I used:
67-1548-1-ND (0603 SMD LED) ($0.125 USD each)
SAM1002-11-ND (11 position Low Profile Header) ($2.59 USD)  These are connectors for the Volume display
SAM1109-11-ND (11 position Low Profile Receptacle) ($1.68 USD)  These are connectors for the Volume display
SAM1112-12-ND (12 position Header) ($2.08 USD)  These are connectors for the Balance display
SAM1122-12-ND (12 position Receptacle) ($1.51 USD)  These are connectors for the Balance display

I also replaced the Output Amp Trim Pots (R226 on the "5" boards).  I have posted information under the Hot Amplifier thread.

Hi

Thanks for all of the detailed information and photos.  It gives me a lot of incentive to do the same job myself.  The display has come up really well and looks fantastic.  I think that I will start on one of my old BC9000 displays first to get a bit of practice.

Well done - you have fixed an age old problem

Geoff

Hi everyone

Just an update on this project.  Using all of the information from this interesting thread, I have spent the last few months working on some of my faulty displays.  The following points might be useful to anyone who is thinking of undertaking a similar project.

The 0603 SMD LEDs (14mcd) were easy to get and have worked well.  It took me some time to develop a good soldering technique (I have now used 60 LEDs out of my reel of 100) but you do need a good iron and some very fine solder.  I also had to make a special shaped holder from a wooden barbeque skewer which keeps the microscopic LEDs in place during the soldering process.

Removing the display from the main PCB was fairly easy but I don’t want to do that too many times for fear of damaging the main board.  I purchased the parts that have been listed for the header and socket connections but never installed them for a few reasons.  The balance display on the BM8000 has pins which are very long and I thought that the header and socket assembly was too short.  Some of the pins are also bent which makes the job more difficult.  Finally, I wondered if I would ever be able to get the whole display reassembled because the plastic support only has limited flexibility.  Even reassembling the original pins was hard enough.  I’ll need to build up more confidence to do that job!

My balance display was suffering from three failures so I decided to replace all 11 LEDs.  This task was easy once the display had been dismantled and the small PCB held nicely in a vice.  With this job, I learned that any of the existing LEDs that are working can be very easily damaged when the white plastic part is removed.  The white plastic has to be lifted off very straight so that it doesn’t hit any of those small wires.  The same goes for putting it back in position.  On my first attempt, the number of failed LEDs increased from 3 to 5 simply during the dismantling process.  Thereafter, I took much greater care during dismantling and re-assembly.  Fortunately, the 0603 LEDs are much more robust and will take a lot more knocking – part of the benefit for deciding to replace the lot.

My TP8 display only had one failed LED so for this one, I decided to just replace it with the 0603.  I carefully took the display apart and was able to swap the bad LED without damaging any of the existing ones.  The only problem was the fact that the new LED is significantly brighter than the older ones.

During the reassembly process, I decided not to glue the red lens cap or the white plastic number mould to the back of the display PCB.  These parts have a very snug fit in any case and gluing didn’t seem to be essential.  It also means that when the complete display is resoldered back onto the main board, you can remove the lens cap and mould to access any faulty LEDs, without having to unsolder all 18 pins again.  This proved to be a useful approach when it became clear that one of my LED solder joints was less than perfect.

Being able to remove the lens cap easily, I then experimented with the problem of the single bright LED.  My final solution was to put a small section of photograph negative over the segment, on top of the white plastic and held in place by the lens cap.  This very simple solution has resulted in all of the segments in TP8 having a uniform intensity and the results look very good.  When I find a larger piece of suitable negative, I will slip it over the balance display and that will equalise all of the intensities between the four displays.  At the moment, the balance display is slightly brighter but as someone has already mentioned, this display is hardly ever switched on.

I now have some single segment failures to do on my BC9000 and with the techniques that I have learned so far, I am confident that I can get a good looking result that restores the full capability of the unit.  It is funny how much less satisfying these units are when the displays are faulty – restoring those little lights has somehow made the sound that much better.

Thanks again for everybody’s help, I continue to learn so much from you all.

Regards from

Geoff