LED Christmas Light Repair





Introduction: LED Christmas Light Repair

Christmas lights are a real nuisance to repair.  The hard part is finding the bulb that is burnt out and most people do this by trial and error.  If you have a string of LED lights that are of the non-replaceable type you may think all is lost.  But don't be too hasty.  What if you could find the problem LED and then repair the string.  Let me illuminate the solution.

You will need some tools that most people who tinker with electricity will have.


The following involves working with electricity.  Electricity can kill you if you don't know what you are doing.  So if you are not qualified to repair devices that require electricity then don't attempt the following repair.  If you do follow these instructions then you take full responsibility for getting electrocuted  - which as mentioned previously can kill you - or for any other risks associated with the activity outlined in this set of instructions.

For example, if you burn yourself with the soldering iron that is your fault.  If you get lead poisoning from eating the lead solder this is you fault.  If you burn down your house because you did not insulate your repair properly this is your fault.  If your spouse whacks you with the rolling pin because you destroyed his/her Christmas lights guess what - your fault.

Step 2: Tools and Materials Required

The tools needed are:
Voltage Detector (see picture for example)
Soldering Iron
Heat Shrink Tube
Wire Cutters
Wire Strippers

Step 3: Circuit Explanation

I am working with a 70 light string which consists of two parallel circuits that have 35 lights each in series.  When one of the LED's fails the circuit breaks which affect all the other lights (half of them) that are in the same series circuit.

Another factor to consider is the current limit of an LED.  LED's do not like a lot of current so besides the LED there is also a current limiting resistor in each light.  For this repair we are actually going to bypass the faulty light.  This will increase the current that goes through the remaining lights because we have eliminated part of the resistance.  However, taking one light out should not increase the current enough to damage the remaining LED's in same circuit.  There is of course a limit.  Bypassing any more that two lights in the same series circuit will likely increase the current enough to put the remaining LED lights in jeopardy which will definitely destroy the entire half of the light string.

Step 4: Detection

The fist step is to find the LED that is no longer working.  The non working LED will obviously be in the string half that is not working.

With the lights plugged in, use the voltage detector to check the live voltage wire between each light, starting at the end that plugs into the wall outlet. There should be voltage detected at the live wire going into the first light.  Then check the wire that goes from the first light to second light.  This is assuming that the first half of the light string is not working.  If it is the second then start at light 36 for a 70 light string.

Keep checking for voltage between the lights.  As soon as you find a wire between the lights that no longer has voltage detected the light prior is likely the light that is fault.  As an example, if there is voltage on the wire between light 6 and light 7, but there is not voltage between light 7 and light 8, then light 7 is likely the problem.

Just to make sure test for voltage between the next set of lights just to make sure.  There should be no voltage detected.

Step 5: Verification - DO NOT ATTEMPT

I did this to prove a concept.  It is not part of the instructions.  You could get electrocuted.

When I was sure of the LED that was faulty I unplugged the lights from the electrical source and then put a sewing pin through the wires going into the LED to bypass the light in question.

After making sure the pin was not touching anything conductive I plugged the lights back in and the light string half that did not work before now worked except for the light I bypassed with the pin.  This proved I found the faulty LED.

I then unplugged the lights and began the repair.

Step 6: Repair

At this point I cut the wires going into the faulty LED, put on my heat shrink tube (2 tubes), soldered the wires, and shrunk the tube.

Step 7: Conclusion

With the faulty LED light removed the light string half that did not work is now working minus 1 light.

As I mentioned earlier the removal of a light will increase the current and LED's do not like high current.

I measure the current in the light string half that was not faulty and it was 9mA.  Measuring the current in the light string half with the one light removed the current was 12mA.  The general upper limit for LED's is 20mA so the current level is still reasonable even with the one light removed.

I am happy to say the lights are still working fine after two weeks.



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    In the example, when the faulty led was found, it was not replaced, it was "cut out" and bypassed. Can't one simply put in a "good" led to fix the problem?


    On my string the voltage between the LED and the common is 3V. The Voltage detector spec for the ones is see on line are between 50v to 1000v or 12v to 1000v. How can I use the detector? Is there something I am missing?

    I am looking for a new conclusion. The 2nd half of my 50 light C7 led string is not lit. My voltage detector indicates power right to the last bulb and the next plugged into it works. Thoughts??

    A little off the subject, but someone mentioned scouting and I thought I'd expound on that just a little bit. There's WAY more to scouting than campfires and singing Kym-Ba-Ya (although there's that too). A lot of life's lessons are taught in scouting, and practical things like how to fix a broken wire or how to do one of those McGyver projects where you make do with what you've got to make or do something practical. It's these kinds of activities that give scouts a heads up in the adult world which some of them are about to enter.

    I accidentally came across a solution to finding which are bad and which are good LED's in a string. I think so, but, check it out and comment.

    Plug in the LED string. It doesn't matter if it or the section in question lights or not. Now, examine in a darkened room or dark shade. There will be a faint (and I mean FAINT) blue glow--a tiny dot--in every good LED. Bad LED's will have no faint blue dot of light. Let me emphasize the words 'faint' and 'tiny' again.

    Let me know if this proves out to you. For me, no-blue-glow correlated with LED's that were bad. In each case, one leg of the LED had broken off (seems like a sucky material design mistake.) My strings were two quality strings of 100 lights purchased at Costco, and they made it through last season. Winding on a spool for storage probably disturbed the delicate LED leads. I was only able to repair one of those strings where I was able to find the one (1) bad LED and the whole thing LIT! The other had far too many bad LED's--far more than I had replacements for.

    If this proves out, all that I humbly ask is that it forever be known as The Allen Whitlock Method. :-) (Book available on Amazon.)

    We just repaired a string that was half out with this method - one bulb did not have the FAINT TINY GLOW (TM) you described and we replaced that bulb and the string sprang back to life. Thanks!!! (with lots of extra exclamation points)

    we tried this on 2 sections that were out, we found no blue glow anywhere. Maybe it doesn't apply to colored C6 lights......

    If an entire section is out (no blue glow on ANY LEDs,) I have to wonder if that is a wiring problem rather than individual LEDs. Or, it could be that the thick covers are obscuring the glow.

    Lisa, Sorry to hear that. The C6 lights have a faceted plastic cover. The lights I was using have a clear, small and thin cover.

    You bring up a flaw in my scheme. I have not tried this except on the lights I was using.

    From an ad for C6 lights: "The decorative, faceted lens diffuses the light creating bright attractive colors perfect for any indoor or outdoor displays."

    This is my first attempt with fixing LED light strings. I have 3 matched strings with icicle covers over the light, and one string stopped working, and I need all three, but can't find a replacement. Using your idea to plug in the string in a dark room, I can see 13 out of 30 LEDs that faintly glow. The other 2 strings don't have a single LED not working. Does it sound possible that this one could have 17 out of 30 go bad all of a sudden? I removed 2 LEDs that did not glow, and replaced them with the 2 spares that came with the set, and one of those glows. Are all the ones not working really bad or can something else be wrong. The ones that don't work are not all together...separated by working LEDs. Is this string unfixable, short of finding a bunch of replacement LED to fit this set?

    I don't know about the icicle lights. If a whole section is bad, I think it's natural to suspect a wiring fault, rather than the mass death of individual LEDs.

    But you did see the faint glow--that's some confirmation that it may be helpful, IF there is power to a section in the first place.

    I am disappointed in LED lights--they seem not ready for outdoor, unsheltered, winter use. You're presenting a problem that's over my head. I'm not an electrical engineer--I'm just someone who is sharing what they noticed (the lack of a faint blue glow on bad LEDs.)