The Workbench

Re: Rebuilding Beomaster 8000 Displays

geearr — Thu, 09 Jul 2009 22:14:42 GMT

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

Re: Rebuilding Beomaster 8000 Displays

geearr — Thu, 12 Mar 2009 17:34:15 GMT

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

Re: Rebuilding Beomaster 8000 Displays

GDSammet — Thu, 12 Mar 2009 13:39:58 GMT

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.

Re: Rebuilding Beomaster 8000 Displays

auric — Mon, 16 Feb 2009 23:41:40 GMT

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

Re: Rebuilding Beomaster 8000 Displays

GDSammet — Mon, 16 Feb 2009 17:41:11 GMT

Derek

Your explanation makes sense. I had broken wires at the LED side, not the pad side. I removed all of the broken LEDs from the board, so I cannot provide a picture of the broken wires. So, in my case the paste would not have worked as you explain.

Gerhard

Re: Rebuilding Beomaster 8000 Displays

auric — Sun, 15 Feb 2009 20:33:10 GMT

Hi Gerhard:

Well one side of the LED sits on the pad. And the wire runs from the silicon waffer outside to the other pad. The silicon junction is encapsulated in red epoxy. I believe its where the wire connects to the other pad (ie out side world) that gets severed. So you need to put a pool of silver solder paste over that pad to bridge the gap.

If the wire is broken on the LED side then there's nothing you can do.

Derek

Re: Rebuilding Beomaster 8000 Displays

GDSammet — Sun, 15 Feb 2009 12:35:05 GMT

Derek,

Thanks for the compliments on the picture. I love close up macro photoghraphy. I have a closeup shot of a single dew drop on a spider web. It's amazing!

I thought about your suggestion on the solder paste. I'm just not sure what the wire is connected to on the LED. I wasn't sure if there was some microscopic connection. Maybe I'm thinking of it like a normal lightbulb, and the LED has connectivity all the way around?

Gerhard

Re: Rebuilding Beomaster 8000 Displays

auric — Sun, 15 Feb 2009 05:07:09 GMT

Gerhard:

This is a beautiful picture. Your photography skills clearly exceed mine!

Perhaps you can take a picture of one of your faulty leds?

You are absolutley correct about the molded SMT Leds being more rugged. I don't think the LEDs actually "burn out." It's that wire that you show that becomes disconnected.

One less invasive solution (replacing all leds) that may work is to use silver solder paste (the type used in prototyping to draw conductive traces on PCBs or used to repair PCBs). Deposit a large amount of the paste on the pad and hopefully it will restore the connection.

Derek

Re: Rebuilding Beomaster 8000 Displays

GDSammet — Sat, 14 Feb 2009 17:44:15 GMT

I wanted to share my picture of one of the LED segments when it still works. The total width of the LED and wire is 1.0mm. The LED by itself is .5mm. Modern LEDs have the LED and wire molded into a plastic housing which makes them much more reliable and durable.

Re: Rebuilding Beomaster 8000 Displays

Craig — Fri, 13 Feb 2009 19:29:41 GMT

Derek, I take my hat off to you. Don't think I would even start to attempt a job like that.

Craig

Re: Rebuilding Beomaster 8000 Displays

Jandyt — Fri, 13 Feb 2009 09:10:12 GMT

Well done Derek!
I am impressed with your patience.
Thanks for sharing this with us.

Andy T.

Re: Rebuilding Beomaster 8000 Displays

soundchoice70 — Fri, 13 Feb 2009 08:40:14 GMT

Hi Derek and Martin,

Thanks for both your replies... obviously from what you both say, this job is not for everyone, I guess I'm just trying to understand from both of you the complexity, for both my own reference and of course the many beoworlders out there who may have units suffering from this... to determine the options available...

Derek, just to let you know this is not a job for me... I couldn't even handle a simple speaker cap replacement! (with Martins very clear instructions no less) But thanks for your detail description, it will definitely prove useful for many more capable owners...

The reason I was asking you both if an average 'technician' could handle this is to determine if the kits could be ordered from Martin or the parts you list for instance and installed ... From what you both advise its most likely a bit of a gamble, so its probably best to get the displays removed and send them to Martin for rebuilding...... unless of course you want to start this part time...

Thank you both and have a great weekend ahead!

Laurence

Re: Rebuilding Beomaster 8000 Displays

Dillen — Fri, 13 Feb 2009 04:06:53 GMT

Laurence,

I'm still doing most of the rebuilds here on displays and/or boards sent to me.
Handling, let alone soldering, 0402 LEDs (the whole component is only 0,5 x 1,0mm)
is not something "every technician" can do easily but there are some who can and
for them a DIY kit is fine. It also contains other components to convert the rest of the
machine for the rebuilt displays, these will have to be replaced regardless of
who rebuilds the displays, they are mainly resistors and are as easy as
the cap kits when the displays are done.
The displays will need to be dismounted from their boards.
It's very hard to do anything with tiny components on a sloping board.
Besides, in some machines some resistors that needs replacing are sitting right under
the displays so are not easily accessed otherwise.
But as Derek (and others) have just proved, I'm far from the only one who rebuilds
displays and geographically Derek is far closer to you than I.

Martin

Re: Rebuilding Beomaster 8000 Displays

auric — Fri, 13 Feb 2009 03:59:12 GMT

Hi Laurence:

I think you have to be more "creative" than simple capacitor replacement; the task requires much greater skill and dexterity.

First you must disassemble the LED modules which requires desoldering multi pin devices! The B&O pcbs are not very high quality and so you must be very careful because you can damage the traces! Best to use a desoldering pump to suck up the solder. Too much heat will also damage the traces.

Once modules are removed, you must then dismantle the lens which involves cutting off the plastic pegs. Later on you use epoxy to glue the lens back on.

Once inside you need to remove the old LEDs and solder the new ones. If you don't have stable hands, the task will be nearly impossible as the parts are very very small.

I guess if you are good at soldering and desoldering it shouldn't be a problem. The trickiest part is really holding the smt LED stable while soldering one end. Once you have one end soldered the other is easy.

You should also buy plenty of spares. I ruined several LEDs before I finally go the hang of it!

I hope this helps.

Derek

Re: Rebuilding Beomaster 8000 Displays

soundchoice70 — Thu, 12 Feb 2009 22:18:37 GMT

Hi Derek,

Thanks for your reply and additional information... I think your report on doing this made it sound relatively easy for someone who knows their way around the electronics. But it does look rather time consuming and requiring lots of patience and steady hands... no coffee before hand....

So I'm wondering, what would you rate this in difficulty/complexity/labour intensity compared to a capacitor replacement? I recently had my system recapped with one of Martins kits by a local service centre, so I'm wondering for those of us who would need to go this route, would they be able to do this kind of repair?

I had wondered about off the shelf segments myself, but I guess sizes, specs etc may be difficult to match and source?

Hi John,

Yes , actually i did know Martin was offering rebuilds on the displays. I actually had one of the tuning arrows fail on my system which I thought was LED, but Martin came to the rescue and supplied the simple lamp replacement required!

I think that perhaps I misunderstood, as I thought that Martin only offered the rebuild himself, so it would involve sending the displays, in my case to him half way round the world. It would also involve me dismantling / installing the displays which i really don't think would be a good idea... ... What struck me about this is that someone handy can tackle the whole process themselves.

Anyhow, we'll face this bridge when (hopefully not too soon) we get to it!

Hi Martin,

I didn't realise that you had formalised the DIY kits for the displays... Sorry, obviously behind the times, i was thinking you were still doing all the rebuilds yourself as per my reply to John... So the kits are similar to the caps kits, any technician should be able to handle the rebuild? Thats also very good news!

So it appears this is no longer a headache, as we have a couple of good options to choose when resolving the failing LEDs.

Thanks

Laurence