Faulty LED in LPD8806 strip

[rintaun]

I recently ordered 5m of the addressable RGB LED strip, and I've gotten it working great, powered by my Raspberry Pi (super simple with the SPI driver).

There is, however, one caveat. When unrolled, there's one LED right in the middle for which the green simply doesn't work. If I press on it (even very, very lightly), it begins to work, which makes me suspect that one of the connections is loose in there, either on the chip or one of the resistors, I'm not sure -- it's hard to see clearly. Here's a video showing the problem: http://youtu.be/4Txgf4lEuJI

And here are a couple pictures:

http://i.imgur.com/BeRLv.jpg
In this picture, the entire strip should be yellowis (green + red), and it is, except for this one little sad LED

http://i.imgur.com/vMHiy.jpg
And here's a closeup of the chip/resistors in question. It seems there's a bit of dust or something in there; that's why it loos so nasty. But this is the best I could get.

[pburgess]

Sounds like a cracked solder joint. If you can get by without the strip being 100% waterproof, you can slice open the covering with an X-acto blade and touch up the suspicious solder connection(s) with the tip of a soldering iron.

[rintaun]

Yeah, I'd thought that might work... I'm a bit hesitant to do it, though, as I'd like to do my best to preserve the waterproofing -- I was considering using the strip as part of my Christmas lights this year. So I'm at a bit of a loss what to do.

[pburgess]

Cutting the end off a silicone cap to make a sleeve might work, then seal it with silicone glue.

[rintaun]

So I went ahead and cut open the waterproof casing to fix this, and I believe the problem is a little bit more complicated that just a cracked solder joint. It looks like one of the components (a capacitor?) itself is cracked. I took a couple pictures that show the problem -- you might not be able to see it at the lower resolution, but if you view the full resolution images, it's pretty dramatically visible. How should I proceed from here?

On a side note, it's amazing the detail missed by the naked eye -- I can just barely see a crack without magnification, but zooming in, it looks pretty smashed.

[adafruit]

try removing the capacitor with a soldering iron

[rintaun]

Will removing the capacitor fix the green LED? Won't I still just have the same problem? I'm pretty inexperienced when it comes to electronics, but it seems that if removing the capacitor would fix it, it should already work with a broken capacitor... Am I missing something?

[adafruit]

if its cracked it could cause problems, id remove it, then you can try resoldering that resistor next to it or replacing the resistor with a small piece of wire (its OK to do this)

[Snapper]

similar problem with a broken resistor:

RB , RG and RR on LPD8806 Stripes has 1,5 Ohm 1R5 for all colors the same ?
Forward Voltage is for the red led different !
Red 1.80 --- 2.40 V
Green 2.80 --- 3.60 V
Blue 2.80 --- 3.60 V
for HL1606 stripes use for Blue - 130, Red - 150 and Green - 180 ohm ?
Forward Current is 20 mA for all colors the same !
somehow confuses me that all !

1r5.jpg (51.43 KiB) Viewed 1603 times

[adafruit]

its a constant current chip, the resistors are there mostly for 'show'

[rintaun]

Out of curiosity, what would the motivation be to include the resistors, in that case?

Wouldn't omitting them reduce the cost and complexity of production, in addition to reducing the number of possible points of failure?

[adafruit]

could be a small resistor helps avoid a total short, or maybe it helps with balancing?

[rintaun]

Well, I tried everything suggested in this thread, but as it turns out, even after removing the faulty resistor/capacitor, one of the colors in the RGB LED was burnt out. So all told, I ended up just cutting out the offending section and reconnecting the other ends back together, which worked well enough, and I only lost about two inches off the total length, which isn't that big a deal.

Thanks for your help!