How to tell if a pixel is going bad?

[akakfreeman]

I saw something on one of my strings last night that has never happened in 4 years! I have a strip of WS2811 with 40 nodes, 3 pixels per node (bad choice, but I didn't know what I didn't know at the time). At the end of that string I have an extension to some candy cane props with a booster between the first string and candy canes. 

I ran the show for an hour + and all was well. Sunday and Monday these same lights worked well from 5:30 to 11pm. Then I noticed that the candy canes were not working well. Just a few lights were coming on and I noticed that the first string of 40 nodes (the led strips) looked to have power injection issues. The top of the string was white, but as you got to the end it was turning yellow. The Red, Green and Blue looked reasonably okay. I'm only running lights @ 20%.

I turned the show off. Waited a while and turned it back on and all was well again.

I'm wondering if someone of the pixels in the led strip might be starting to fail as they get warm or something? Does that happen? Yesterday was also very warm (hit 78 degrees). Today I did a test and all is well, but it's only 48 degrees (Texas 30-40 degree swings in temperature). I'm leaving them on for a while to see if it starts to degrade again.

I've wondered if I should inject more power, but since it works fine at times I'm not sure that is the cause of the problem. Any ideas?

[JonD]

5v lights, 12 lights, how many lights are on the string, how long are the extension cables between the controller and lights?

White to yellow, could certainly be power issues.  40 nodes is not very many lights.  20% power is low, you might try bumping up the power to 30-40% or more to see if it makes a difference.

Typically bad pixels are obvious.  All the lights work to a certain point, then something bad happens.  They display the wrong color(s), don't turn on.

[rayster]

I do a voltage test at the end og every group of lights. I took a connector and put banana plugs on the wire end so I can just plug the connector at the end of the string an plug the banana plugs into my volt meter. Using 12 volt string I will test at the end of each string if it is under 11.5 volts I add power.

[akakfreeman]

Thanks for the ideas. The show has been running fine since this one-time anomaly. I like the idea of making a connector with banana plugs to make it easy to check the voltage (12v).