As many of you know, there’s been a dead pixel on the LED wall for a while. I took it down and fixed it tonight. It appears as though the pixel was replaced once before (solder job and missing corner pixel), so I don’t know why it might have failed again. The pixel was receiving data and displaying fine, but it wasn’t passing data out to the next pixel (although sometimes you could coerce it to with enough fiddling).
I swapped the faulty pixel with the last pixel in the strip (because the last pixel doesn’t need to transmit data). Note that the other 8x8 grid of RGB LEDs on the shelf with all-black wires are probably a different chip, as I tried to use some of those, but the bit pulse timings seemed to be incompatible with the LED wall’s LEDs (checked with the oscilloscope). It would (almost) never light up, and would transmit nothing but zero-bits to the next pixel.