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LED Christmas lights gone dim

Discussion in 'LEDs and Optoelectronics' started by KMoffett, Dec 15, 2016.

  1. KMoffett

    KMoffett

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    Jan 21, 2009
    We have three strings of LED Christmas lights in series around our porch. Last night, my wife noticed that the middle string in the series was out. The two strings on the each end were fine. My grand daughter said "granpa, they're not out, just dim". I brought them in, and she was right. You can hardly see the light in the bulbs. All LEDs are lit, but very, very dim. I have no idea of how these are wired. I haven't done testing yet. Any suggestions?

    Ken
     
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    I found a string of Christmas tree LED lights that were thrown away. Of course they did not work. I unscrewed the cover over an LED and the LED fell out. Its leads were not connected but were simply touching the wires of the string. Some of the LEDs have their leads and/or the string wires corroded where they touch together. Cheap junk.
     
  3. KTW

    KTW

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    Feb 22, 2015
    Are they a different wattage?
     
  4. KMoffett

    KMoffett

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    Jan 21, 2009
    All three strings are the same.

    Ken
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Do they run from line voltage or something a lot lower? If they run from a high voltage it may be that it is actually just one string with a simple single point failure
     
  6. KMoffett

    KMoffett

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    Jan 21, 2009
    110VAC. Two prong plug on one end and two prong socket on the other, so several strings can be run in series.

    Ken
     
  7. shrtrnd

    shrtrnd

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    Jan 15, 2010
    My thinking is along *steve*'s .
    You've got a single point failure in the dim string.
    Sounds like a job for your granddaughter. I'd ask her to help you out by pulling and replacing each LED bulb
    in the one string, to try to localize the socket (or bulb) that's the culprit.
    Who knows, maybe she'll become an electrical engineer out of this.
     
    MWD likes this.
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    The LED string that I found had corrosion in a few spots where the LED wires simply touched the string wires making a poor connection. At least one LED had one of its wires severely corroded and ready to fall off. That would cause dimming before complete failure.
     
    MWD likes this.
  9. MWD

    MWD

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    Dec 10, 2018
    Had the same issue. The culprit was the resistor at the end a string of LEDs. You can find it inside a little weatherproof cap along the string. A 50 cent fix at an electronics store. In my case it was a 1.8K Ohm 5% 2W resistor. Just replace with the leads bent upwards inside the holder.
    -M
     
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