Hi, I have two neopixel matrix 8x8 each. If I test each one separately with the Adafruit strandtest example, everything works perfect, change and try the other one, and everything is great; BUT when I connect them nested, I mean DOUT from first goes to the other DIN and +/- are connected to external power supply and all - are ground common, only the first one shows.
I changed the from 64 to 128 (#define LED_COUNT 128) but nothing. I can see that is looking like is taking some extra time to process the other 64, but nothing. I tested in Arduino Mega and ESP8266 with same result. Anyone expirenced this behavior?
Please post your test sketch, using code tags when you do
Could you post a pic of the soldering connections you made?
When you ohm out the connections they all looked good?
What I did wrong the first time was that I connected from DOUT instead of DIN, first led had low light, then when I recheck I found that I did backwards. Did I burn? Cause it's rare that individually, they do work perfectly. 
2 panels, pA, which works and pB, which has not worked. Unplug pA, Plug Pb into Pa's slot. Does Pb work?
Both of them (pA & pB) separately, they run perfect. If I nest, only the first works. I also tried pA(DIN),pA(DOUT)- to pB(DIN), nothing and the just switched pB(DIN),pB(DOUT)- to pA(DIN). Nothing happens, only first.
The ONLY thing I changed in the example code is the LED_COUNT.
Also, if I put them in parallel, the both run perfectly (they do same thing, of course and led count =64)
Please post the code that you ran when you had 2 panels in series, ie Arduino pin to Panel A DIN and Panel A DOUT to panel B DIN with both panels powered, of course
Can you please check that you are actually getting 5V into the second panel when they are connected in series ?
Coolies, we now know the program can run a panel and that both panels are good.
Oh nesting means something different, but daisy chaining, as in this case, works.
Waiting to see what the V's are on the pin going to the daisy chained matrix. And you might as well ohm out the ground and data pins. Now you may need to supply power directly to the 2nd daisy chained unit if 5V is not present. Also, that breadboard can only supply a limited amount of current. And where is the 5V coming from?
NeoPixel indicates you may need up to 3.5 amps per panel.
I agree with @Idahowalker, I would connect the 5V supply to the second matrix as well as the first. There may not be enough current passing through the first matrix to power the second.
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