Possibly defective NeoPixel strip

EL Wire/Tape/Panels, LEDs, pixels and strips, LCDs and TFTs, etc products from Adafruit

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azimmy
 
Posts: 6
Joined: Thu Feb 06, 2014 9:57 pm

Possibly defective NeoPixel strip

Post by azimmy »

I bought 3 meters of the 30 pixel/meter sealed NeoPixels (product 1376) for a light project I'm working on. As soon as they arrived I cut 6 LEDs off of the tail end of the strip and used them to test my LED control code and power supply hardware. The rest of the strip went back in the box. Once I perfected my hardware and software using the short test strip, I hooked it up to the 90 LED (now 84 LED) strip, but couldn't get any sign of life from it. It's the same hardware and code that works 100% of the time with the 6 LED strip, but can't get any sign of life out of the larger strip. I've confirmed that the long strip is receiving power and verified on an oscilloscope that the signal is being received. The signal looks good and matches the expected timings. I even hooked up the Dout pin of my 6 LED strip to the Din pin of the long strip, then sent it 10 lights worth of data, but this still didn't work.

I suspected that the first pixel in the long strip was defective and not passing data on to subsequent pixels, so I cut it off and tested it individually. Even by itself, the pixel wouldn't work at all. I noticed that the pixel was almost off of it's solder pads, it actually looks like the pick and place machine was misaligned. I touched up the pixel solder a bit by hand and it works perfectly. Here's a before and after of the single pixel I cut off of the long strip:
Single LED before soldering. Possibly misaligned solder joint is difficult to see in this photo
Single LED before soldering. Possibly misaligned solder joint is difficult to see in this photo
IMG_20140217_181445151.jpg (58.22 KiB) Viewed 272 times
After soldering the joints on the right side by hand
After soldering the joints on the right side by hand
IMGP0654.jpg (271.29 KiB) Viewed 272 times
Once I realized that the LEDs might not be soldered properly I took a closer look at my test strip of 6 LEDs and the long strip that won't work. All 6 LEDs in the test strip are perfectly centered on their solder pads and each pin is clearly visibly soldered down. All of the LEDs in the first segment of the long LED strip are all nearly off of their solder pads, just like the single LED I repaired by hand. Here's a picture of the long LED strip. I've hit the limit of 3 attachments per post, so I'll post a close-up photo of the long LED strip in a reply.
Long LED strip and power connector
Long LED strip and power connector
IMGP0648.jpg (340.77 KiB) Viewed 272 times
I'm open to suggestions about what could be wrong here, but I strongly suspect that the first segment of my LED strip is improperly soldered, especially since the only thing I changed to get one of the lights to work was touch up the solder joints. I've followed all of the best practices from the Adafruit NeoPixel guide (http://learn.adafruit.com/adafruit-neo ... /overview), and I'm very certain that I didn't somehow "fry" the whole LED strip.

azimmy
 
Posts: 6
Joined: Thu Feb 06, 2014 9:57 pm

Re: Possibly defective NeoPixel strip

Post by azimmy »

Here's a close up of the first pixel in the long pixel strip. It's difficult to get a decent photo through the weatherproof strip, I apologize. This pixel has never shown any sign of life.
IMGP0642.jpg
IMGP0642.jpg (288.89 KiB) Viewed 271 times

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adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Possibly defective NeoPixel strip

Post by adafruit_support_mike »

That looks like a sign of uneven heat in the reflow oven.

A little misalignment from the pick and place machine is acceptable.. once the solder melts, its surface tension tends to pull the components into place. The surface tension can also cause problems though. If the solder on one side of a part melts or solidifies before the solder on the other side, it can pull components out of position.

It sound like your strip had some marginal joints, and that's a quality issue we'd need to discuss with out supplier.

Send a note to [email protected] with a link to this thread and the folks there will get you a new strip. They may also want to arrange return shipping for the one you have so we can take a closer look at the joints ourselves.

azimmy
 
Posts: 6
Joined: Thu Feb 06, 2014 9:57 pm

Re: Possibly defective NeoPixel strip

Post by azimmy »

Great, thanks for the fast reply! I've confirmed that the solder joints on some of the pixels are bad by poking through the weatherproof strip with a header pin soldered to some wire and poking the Din line. The front 5 pixels are indeed defective.

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