Troubleshooting LED light issue

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  • MattM
    Member
    • Dec 2016
    • 41
    • UK

    #1

    Troubleshooting LED light issue

    Hi,

    I have been asked to have a look at a LED Christmas light string on a 2ft snowman. It is a basic LED string wrapped around a wire frame.

    The PSU is a 240v stepdown to 24v 580ma 10.4VA.

    The voltage at the string appears to be fine but the string won't light. The string is not open circuit. I was told that it lit for about 30 minutes and then failed and has not come back again.

    I am guessing I have a duff LED/resistor in the string but have no idea how to fault find this easily. If it was AC I would have used a tester pen at each LED but clearly I can't do that as it is DC.

    Any suggestions would be gratefully received.

    Thank you
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30994
    • Albion

    #2
    Re: Troubleshooting LED light issue

    i use a pair of syringes used as needles to poke through the insulation onto the led legs - then short them to bypass the led.

    most common failures for me where blue - for some reason, as they in theory have the higher operating voltage.

    Comment

    • MattM
      Member
      • Dec 2016
      • 41
      • UK

      #3
      Re: Troubleshooting LED light issue

      Thanks very much for this, will give it a go

      Comment

      • MattM
        Member
        • Dec 2016
        • 41
        • UK

        #4
        Re: Troubleshooting LED light issue

        I spent some time with this and established that the PSU was in fact at fault along with a bridge rectifier which was inline with the cable to the lights.
        I removed the bridge rectifier and the unit now works but the lights flicker presumably because the bridge rectifiers is not in series.
        It was installed inside a weather proofing fitment and I had to cut it out. It is a DB107S. What I don't know though is what the wiring diagram for it was as I had to cut it out. Has anyone any ideas and if I simply leave it out is there any risk to lights - the flickering isn't that bad?
        Thank you

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 8132
          • Canada

          #5
          Re: Troubleshooting LED light issue

          add a capacitor? What does this thing look like? Any pics?

          Comment

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