How to troubleshoot a (possibly fried) ws2812b led strip

Question

I have a 4.5m, 60led/m Ws2812b strip, hooked up on a raspberry pi running hyperbian.

Raspberry works on its own psu, and I have a meanwell 5v 18a for the leds with common grounds.

The setup was working great for some time until I decided to inject power at the end of the strip as it had some dfferences on high brightness whites.

I soldered the extra 5v and ground at the end of the strip and it worked wonderfully.

While trying to cable manage, the 5v+ wire got loose and short-circuited something. Probably the signal line?

I should note that the end of the strip is very close to the start, so that loose 5v could have touched anything.

Since then I cannot get the leds to work.

I multimetered along the strip, it seems to have a constant ~5v power everywhere.

I have tried a second raspberry pi (in case I fried the gpios on the first one) but I get the same behavior from the second rpi too

What are the steps to figure out if it's fried or if it's repairable?

Thank you.

Answer 1

The first two leds were the problem.

I tried everything, connect power and ground and move the signal cable around, trying in every position, even cutting the first led didn't fix it.

I had to remove (cut off) the first two leds in order for it to work.

Thank you

Answer 2

To explain the other answer, typically if you short out the data input to a given IC, then often only that specific IC will be fried. The input buffer or circuit could burn out while the rest of the chip is fine, or in this case the rest of the circuit/strip/ics are fine.

It's common to provide the first led ic in a stripe a lower voltage when using a 3.3V microcontroller as a level shifter, to take advantage of the isolation between the ICs. In a short situation, the same happens. The ICs become sacrificial and help save the rest of the strip.