Christmas Lights

Every year when we start our decorating for Christmas, there is always at least one string of lights that burns out. Often, like this year, even though we check all of them before putting them on the trees, one or another go dark after an hour, a day or a week. Forty years ago when I bought my first strings of lights, I would buy GE lights made in America. They lasted year after year until the colors wore off leaving me with just pure white incandescent lights. Then along came lights made in China, as all have been for at least the 26 years we have been here on the farm. With them, I know there will be failures every year. We switched over to LED lights three years ago because they use less power to run them and they say the LEDs will last 25,000 hours. All I can say is the wire may last that long, but I have had one or more go out each year. This year Joyce got a set on the tree and it ran for about two hours before flickering and then died. I had to disassemble the garland strings and then remove the lights to work on them. I know it is more expedient to toss them and then buy another string, but I always want to take up the challenge. I used my ohmmeter to try and figure out how the LED string was wired, but nothing made any sense to me. I went online to search for info and got some mixed data. They are wired in series, which my ohmmeter readings could not tell; I will explain in a moment why. The LED lights have a shunt built in so if a light burns out only that light goes out and the rest of the string will remain lit. The LED can short out and the string will still work, so why did mine go out completely? It turned out two lights had burned out and those shunts had opened. Anyone who is an electronic troubleshooter can tell you one open in a circuit is relatively easy to find, but two opens is a whole different animal. I tried doing a front to back check on the LED diodes but they measured open both directions on all of them. I decided to use the continuity function on the ohmmeter and with the proper polarity that would cause the light to come on. When I found the first one that did not light, I thought I was done, but that came at a point where I only had 5 more to go, so I decided to pull out the  rest and check them while I was working on the string. It was a good thing to do, because I found the second one just 2 spots away. One thing I read on line was the different materials used to create the colors of lights require different voltages to operate. The entire string requires a 120 volt connection which is rectified in half and changed to a DC voltage. That DC is distributed across the string. The material that produces the blue light requires more voltage, hence more current to light that diode. All of the failures so far have been the blue LEDs. So those are the ones to check first, or try replacing first. Every string has 2 replacement LEDs that come with it. The strange thing is none of the 2 dozen strings we have has a blue replacement. They are all a red and a yellow LED. The LEDs that have a cover on them, are not as bright as the the blue that is replaced with a red or yellow, but it's not all that bad and the string works.