many times you will find that the failing node is the first one to actually act up.
if a node is acting correctly, it recieves it's information, then lets everything else pass along.
all it does it take a value, and makes the dimming happen for that channel.
ok, now for a failing node.
failing can happen in three ways....
1.) it's dead. you wont see any lights, and there wont be any lit after it. could be a wire cut (open short), or the chip in the node could be fried.
2.) it could be malfunctioning slightly, that node will get wacky colors, but the nodes after it are still acting correctly.
3.) it could be malfunctioning badly, that node will get wacky colors, and so will the nodes after it. (they may be totally different colors, or all the same.
in all three cases, it's the node that's acting up, not the one before it.
it's extremely rare for a node to show correct colors, yet screw up the nodes after it. if this does happen, it's most likely an intermittent short in the wire carrying the data signal.