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LED Component Question: Total Newb Here

gallion311

Jul 13, 2012
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Hey whats up guys,

I admittedly not much of an electronics guys, but I understand the basics and I had a quick (and probably stupid) question.

So I have a party/DJ light thing (the Chauvet DJ Bank) that's just a small bar of LED banks that light up sequentially. One day the blue LEDs just stopped working and I'm wondering if it can be repaired.

So I opened it up and put a circuit tester on the +/- terminals of that bank and nothing.

When I put the circuit tester on the other banks it does light up when that color is lit (so the circuit tester blinks along with the light).

So what does that tell me about the problem? If it was just a matter of replacing that blue LED piece, would the circuit tester still light up, would it still be receiving power?

I imagine it's pretty simple to just order a replacement part for that blue LED piece, but because its not receiving power I'm wondering if that's even the problem (if its something to do with the board I wouldn't even try a repair...)

Thanks guys, any help is appreciated.

Ryan

*I can post pictures of the LED component if that would help, here's an image from the website showing the unit itself:
adjbank-l.gif
 

CocaCola

Apr 7, 2012
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Pictures of the insides would help greatly, both sides of any boards and what not... Try to make them a decent size and in focus, taken outside or with good inside lighting so that there is less reflection and wash out from a flash...
 

gallion311

Jul 13, 2012
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Sure thing, here you go:

image01
DJBank01.jpg


image02
DJBank02.jpg


image03
DJBank03.jpg


In all 3 images, the broken one is on the right. It's worth noting, the board on the broken one has some noticeable clear stuff coming out of each solder point, which is what originally lead me to believe it was fried and could be a simple fix (you can see this best on image02.)

Ryan
 

CocaCola

Apr 7, 2012
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Nothing like cheap Chineese engineering :eek:

Chances are only 1 single LED has failed but due to the craptacular way they wired them all in a single series that single LED will take out the entire display...

Do me a quick test, swap the blue and green lights locations aka unplug the blue and green board and switch them up... Is the blue still not lighting now? This will narrow it down to the LED panel or the circuit, if the blue still doesn't light it's the panel, if the green now doesn't light it the circuit...

The 'clear' stuff you see is just rosin flux, nothing to worry about...

Chances are you just need to unpopulate that blue board of all the existing LEDs and reload it back up with fresh matching blue LEDs... It's best to repopulate all the blue LEDs at this point, it will likely save you grief down the line...

Are you up to the soldering? If not where are you located? I would be willing to help unpopluate and repopulate the board for a small fee (it will only take me about 15 minutes) + cost of the LEDs, that is if you if you are in the US, International shipping would likely be cost and time prohibitive...
 

KrisBlueNZ

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It looks like all the LEDs are connected in series, which means a failed LED or a broken track anywhere will prevent the whole lot from working (like a string of Christmas lights - the older type).

You can unplug the board and test each LED individually, using three 1.5V cells in series along with a series current limiting resistor of say 470 ohms. Connect the ends of the series chain across each LED. You'll soon find out which polarity to use. Don't use a higher voltage because you can damage LEDs if you connect it backwards. A lower voltage won't work for blue LEDs; they have a forward voltage of more than 3V.

If one of the LEDs doesn't light, you could replace it, if you can find a good match or if matching isn't important. You could also replace it with a zener diode that will drop about the same voltage as the blue LEDs (measure this by temporarily shorting the failed LED and measuring the voltage across another LED while it's lit), or you could just short out the failed LED (this will increase the current in the string, and therefore the brightness of the other LEDs, by a small amount).

If all the LEDs are OK it could be a broken track, which could be anywhere. Use a multimeter on continuity range to check each track. Also, flex the board while the board is plugged in and the LEDs are supposed to be illuminated, as often a broken track will make contact when you flex the board (flex the board so it's concave on the track side).

If you're working on the board while it's plugged in and powered up, be careful not to touch the wires and tracks. That number of LEDs in series will have a significant voltage across the string, which could give you an electric shock.

Another possibility that you should check for first is dry joints on the LEDs. A bit of vibration, or heat cycling, or a bump to an LED, or just poor soldering or contaminated leads or PCB copper during manufacture, can cause the solder joint to break away, especially on single-sided boards with no through-hole plating. Examine all the leads carefully on the underside, and again flex the board, both ways, to see if anything has come loose. This would be my first check.
 

CocaCola

Apr 7, 2012
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You can unplug the board and test each LED individually, using three 1.5V cells in series along with a series current limiting resistor of say 470 ohms. Connect the ends of the series chain across each LED. You'll soon find out which polarity to use. Don't use a higher voltage because you can damage LEDs if you connect it backwards. A lower voltage won't work for blue LEDs; they have a forward voltage of more than 3V.

Quicker and easier just use a 2032 coin cell and wedge it into the two legs on the underside... No need to worry about current limiting for a short period as the battery will self limit internally well enough for this application...
 

KrisBlueNZ

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Quicker and easier just use a 2032 coin cell and wedge it into the two legs on the underside... No need to worry about current limiting for a short period as the battery will self limit internally well enough for this application...
Good idea :)
I've just checked on Digikey for high-brightness blue LEDs and the lowest forward voltage specified is 3.2V. I guess at 3V they would probably still illuminate slightly, and anyway a new 3V lithium cell will have a terminal voltage above 3V, so that method would probably work. Still, in this case, I would use a 4.5V test voltage.
 

CocaCola

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Works fine... Trust me 2032 coin cells have been my go to LED tester for many years now...

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gallion311

Jul 13, 2012
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Thanks for the help so far guys, its much appreciated.

Coca-Cola, yes I am in the US, right outside Baltimore, MD.

I have one additional question regarding your suggestions, I've pulled that plug pretty hard (enough to where I thought it was going to break) and they just don't want to disconnect.

Should I be lifting a tab or something, is that greenish liquid (which you can see in image01) some sort of glue that's holding them together?

I spoke with Chauvet today who said that part is $10 + another $10 for shipping so I'm not sure if thats worth it...

I'll keep you posted.
 

KJ6EAD

Aug 13, 2011
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Those connectors do appear to have some kind of locking tab and glue. The glue can usually be defeated with a knife and the locking tab with a small screwdriver or spudger tool.

I think it's more likely that the driver failed than the LED panel, but your swap test will determine one or the other soon.
 
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CocaCola

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I spoke with Chauvet today who said that part is $10 + another $10 for shipping so I'm not sure if thats worth it...

Not worth sending it around to get fixed at that price, if after you find it to be the panel that is a cheap fix...

As KJ6EAD you might have to work some glue on them plugs on the locking tab but they should give away, try lifting the locking tab as suggested with a knife or screw driver...
 

gallion311

Jul 13, 2012
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Alright, another update and unfortunately for me it's not a good one.

So I plugged the working green LED into the blue port and nothing.

Then I plugged the blue LED into the green port and and now it's working.

So this does appear to be an issue with the board, and for some reason that blue plug isn't working...

As stated above, that's just way out of my league and I wouldn't even know where to start in terms of really giving that a serious attempt at a repair.

Thanks for the help though guys, I did make some progress, just not the right result.
 

CocaCola

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Take it apart further and remove the circuit board and post some pictures of the board outside the unit, it might still be an easy repair...
 

(*steve*)

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There should be 4 almost identical looking drivers for the 4 lights.

The first thing to look for is any obvious differences, and then to decide if one of those differences on the blue channel looks undesired (like something burnt, or some odd white residue, etc.)

It could be that all the drivers are OK, ad the problem is a step further back, but best not to jump steps :)
 

gallion311

Jul 13, 2012
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Alright guys, I have some pics of the board, as well as an interesting update on the situation.

So I took the board out last night (but left everything plugged in) and was looking around at all the components to see if I noticed any burns/residue and didn't really see anything unusual.

So then I looked at the back of the board and again didn't see anything unusual.

So then I turned it back on (with the board still hanging out) and magically, all 4 LED's were working! I have no idea if or what I did so I put the board back in and now I'm bak to only 3 LED's working...I figured maybe it had something to do with the board hanging out so I took it back out, but still only 3 LEDs.

So what does that mean? Is there just a loose connection somewhere? My concern is that's probably tough to diagnose/fix...

Anyway, here's the pics:

Front1
Board_01.jpg


Front2
Board_02.jpg


Front3
Board_03.jpg


Back
Board_back.jpg
 

KJ6EAD

Aug 13, 2011
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Congratulations, you have an intermittent. It's probably a cold solder joint somewhere on the blue channel (circled). It could be in the connectors or on the LED board. You can probably locate it by poking around with a plastic stylus or small wood stick while the power's on. Don't use a pencil; they're conductive.

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