http://reefledlights.com/trouble-shooting/ Going the Do It Yourself route will save you close to half the cost of a quality commercial fixture. However everyones experience level is different and stuff happens. We are starting with the most common errors and ways to test for them. Almost all the problems with a couple of LEDs not lighting is due to Poor soldering. Personally my soldering has improved greatly since my first fixture. If you are the least bit unsure of your soldering skills, we highly recommend using the BJB Solderless Connectors or our pre wired strips. Here We are using the Sperry DM-4100 Multi-Meter. It is set to the diode mode and the positive lead is placed on the + side of the LED and the negative on the â€“ side of the LED. We took this one step further and tested the solder connections by starting at the previous LEDs â€“ and the next LEDs +. This test will tell you if you have a good LED. This shows way too much solder. All it takes is a little to spill over the edge to cause the LED not to light. The next two photos are how to test for this using a Multi-Meter.(Click Photo for Full Image) In the above photo the current is traveling through the Heatsink then up the spilled solder to light the LEDs. The below photo shows a simple continuity test. Both show a bad solder.(Click Photo for Full Image) The solution is rather simple. Clean up the solder and re do it. Its not a bad idea to do these tests as you assemble your fixture. It only takes a second and will save you time in the future. This particular fixture worked fine with 48Vdc drivers but when it was upgraded to a single 150 Watt Inventronice the soldering errors became quite apparent at the higher voltage.