2 wire LED Xmas lights - finding fault in 2 clusters

Thread Starter


Joined Jan 12, 2018
I have a set of Xmas lights, 400 of them, using the new 2-wire polarity switching tech. The controller is separate from the plug. They run at 30V DC... The controller died. Having another set I replaced the controller (I know, silly but I thought the electronics just gave up after 3 months of 4 hrs/day - timer) . it worked but I realized two groups of around 40LEDs were not working. While messing around squeezing them, the new' controller dies as well... Darn! Anyway, i took the controller out and connecting the lights straight to the 30V power supply, i get either blue and green or red and yellow depending on polarity. I know this is how it worked..but of course the two groups are still dead. I attach a figure I found of how I think this is wired.

However, I admit I am dumb but how do I find the culprit in every group? And I assume the culprit in each group is shorted rather than burned out and thus the controllers dying? Do I have to test every LED in each group? They are around 40 as mentioned and I would have to strip the heat shrink on each then use some tape etc .. horrible job. Any ideas how to find it and is it actually a short that takes a whole group out? Pretty simple schematic but I am stumped sorry...
(Figure source: https://auschristmaslighting.com/wiki/Controlling-2-wire-Multi-Function-LED-Strings)