Computers & Electronics

Half of String of Xmas lights don't light up.

  • Last Updated:
  • Nov 30th, 2020 3:15 pm
[OP]
Sr. Member
Nov 28, 2019
715 posts
310 upvotes

Half of String of Xmas lights don't light up.

Hi

I pulled out my Xmas lights yesterday and started to put them up when I noticed one of my led strings only half lid up (starting with the light closest to the plug that you would put in the outlet). I took it down to see if it was for some reason because I was chaining the lights together with other strands.

I did some googling and it seems people were saying that there could be a lose bulb or connect somewhere but after trying to take a new bulb and go down the line and see if it works. I tried that but it did not work though since i had to try like 25 of them I could have missed one or who knows.

It also being 2020, I installed some icicle hanging lights and mini lights and they also suffer from the same problem so I have 3 strands with the same problem.

Is there a better way to try to figure out the problem is? 1 strand is less than 2 years old (I thought I kept the receipt but can't find it) and the other 2 strands are 4 years old. Seems kind of a shame to throw them all away.

I saw some videos of people using non contact voltage connectors so not sure if I should pick up one for around $15 or if I am just waiting my time and money.
16 replies
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Aug 15, 2006
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Easiest way to do it is take all the "dead bulbs" out of the string. If you have a 2nd string, pull all the bulbs out that work and replace them with the bulbs that apparently don't work. If the ones that don't work suddenly work on the string, then you know that bulb is fine and it's a different bulb. You can take the bulbs that did work on the one string and put it in the other string to see if it works on both strings. This eliminates the possibility of an issue with the strings. Eventually one of the bulbs wont work through trial and error which will take time to find, but using this method, you will eventually find the dead bulb.

Why manufacturers do it this way is just plain stupid and cheap. It was a much easier system when one bulb died and you knew where it was.
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Aug 29, 2011
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It's cheaper to manufacture light strings in series than in parallel. That why manufacturers do it.

OP will need to check each bulb independently on the dead string.
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mrweather wrote: It's cheaper to manufacture light strings in series than in parallel. That why manufacturers do it.
Oh I know its cheaper thus is why they do it. However it wasn't always this way
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I have a similar issue except it's non-removable LED bulbs. String is triple wired but I do know the two halves are connected by only two cables. Other than to stick pins in the wiring to check the defective bulb, is there a way to check which one is dead so I can bypass it?
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[OP]
Sr. Member
Nov 28, 2019
715 posts
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kcorscadden wrote: Easiest way to do it is take all the "dead bulbs" out of the string. If you have a 2nd string, pull all the bulbs out that work and replace them with the bulbs that apparently don't work. If the ones that don't work suddenly work on the string, then you know that bulb is fine and it's a different bulb. You can take the bulbs that did work on the one string and put it in the other string to see if it works on both strings. This eliminates the possibility of an issue with the strings. Eventually one of the bulbs wont work through trial and error which will take time to find, but using this method, you will eventually find the dead bulb.

Why manufacturers do it this way is just plain stupid and cheap. It was a much easier system when one bulb died and you knew where it was.
So using a voltage connector would not be faster to determine if a bulb is bad or not? I think 2 strings I can do this for sure (just going to take a long time to do) but mini lights I only got 1 set.

If I replace all the bulb and it still does not light up then that means the string is garbage?
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jimbob12341 wrote: So using a voltage connector would not be faster to determine if a bulb is bad or not? I think 2 strings I can do this for sure (just going to take a long time to do) but mini lights I only got 1 set.

If I replace all the bulb and it still does not light up then that means the string is garbage?
You can try the voltage connector, but that's not going to tell you if the bulb is dead or not, it will tell you if the string is good/bad. Sadly what I suggested is the most accurate route as it will tell you if the bulbs are good or bad. Depending on how efficient you are, the process shouldn't take that long
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jimbob12341 wrote: So using a voltage connector would not be faster to determine if a bulb is bad or not? I think 2 strings I can do this for sure (just going to take a long time to do) but mini lights I only got 1 set.

If I replace all the bulb and it still does not light up then that means the string is garbage?
Look for a tear in the wire around that particular stretch of lights.
[OP]
Sr. Member
Nov 28, 2019
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kcorscadden wrote: You can try the voltage connector, but that's not going to tell you if the bulb is dead or not, it will tell you if the string is good/bad. Sadly what I suggested is the most accurate route as it will tell you if the bulbs are good or bad. Depending on how efficient you are, the process shouldn't take that long
Ok, I did this method on the easiest string, I got the good string and then took out all the needed bulbs and replaced every single bad bulb on the bad string. Sadly it did not work.
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jimbob12341 wrote: Ok, I did this method on the easiest string, I got the good string and then took out all the needed bulbs and replaced every single bad bulb on the bad string. Sadly it did not work.
So you swapped out all the bad bulbs with good bulbs and now the good bulbs dont work? If so, the string is toast
[OP]
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Nov 28, 2019
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kcorscadden wrote: So you swapped out all the bad bulbs with good bulbs and now the good bulbs dont work? If so, the string is toast
Yep, and to even for more good measure, we put all the good bulbs back on the good string, then removed 1 good bulb and took all the "bad bulbs" and checked each one on the string, each bulb worked and competed the string of lights so there is no bad bulbs......it is the string.

I won't bother to do the other strings this took a while and almost screwed up somehow were the good string was not even working, but was able to fix it.
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It's not that simple. I had a long LED string composed of 4 in-series segments, each of which had its own voltage converter in a small sealed block at the start of the string. One of the 4 segments would not light up. It turned out that all the bulbs in that segment were fine, but something had shorted out inside the sealed voltage converter for that segment. However on closer investigation it turned out that it had also fried the wiring for that part of the string (no external sign, but copper conductor noticeably burned instead of bright and shiny when cut open), and it had blown one of the two fuses in the plug. Light strings typically have small fuses in the plug, hidden under a little slide-open door. They are the first thing you should check when a string stops working.
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kcorscadden wrote: Oh I know its cheaper thus is why they do it. However it wasn't always this way
They are made to last only one season, once a bulb fails it loses a lot of light.
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Oct 1, 2009
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Led is a diode. You can use a multimeter with a diode setting to check
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What I have realised is that once 10-20% of bulbs go out, it is easier to simply buy a new string for cheap than to try and fix old one.
[OP]
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Nov 28, 2019
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Scote64 wrote: It's not that simple. I had a long LED string composed of 4 in-series segments, each of which had its own voltage converter in a small sealed block at the start of the string. One of the 4 segments would not light up. It turned out that all the bulbs in that segment were fine, but something had shorted out inside the sealed voltage converter for that segment. However on closer investigation it turned out that it had also fried the wiring for that part of the string (no external sign, but copper conductor noticeably burned instead of bright and shiny when cut open), and it had blown one of the two fuses in the plug. Light strings typically have small fuses in the plug, hidden under a little slide-open door. They are the first thing you should check when a string stops working.
Yeah I checked all the wires but did not cut into them, but the first thing I did do was replace the fuses in the plug but no dice.
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The fault has to be close to the first bulb that doesnot work. If the bulbs themselves are functional, then that only leaves the cable. Check for continuity with a multimeter and it should be pretty easy to isolate. It is either the last lit bulb that is not passing on the voltage, or the first non-lit one.
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