How to repair a flickering led lamp

Discussion in 'General Electronics Chat' started by Nicholask, Sep 7, 2016.

  1. Nicholask

    Thread Starter New Member

    Sep 7, 2016
    Hi everyone,
    I was searching for a forum about circuits to post my question and I found this forum with many active users, so here I am and a friendly regard from Denmark.

    My knowledge about circuits is like a novice, like knowing to spot a burned condensator, how and where to order it, and how to hold a solder in my hand without burning myself :) the reason to repair the lamp is because I am very interested in circuits and would like to know more about spotting and repairing them.

    I have a led light, 156 pieces SMD 5736, which suddenly began to flicker. I checked it out and found that two of the smd have a black dot on them, which to me looks like they gone bad and burned out. (image attached)

    My goal is to repair the lamp, and would like to know if it is possible (or what happens if) to remove those two smd from the circuit and solder a cable or something else instead? Can you point me to a solution to repair the lamp?

    Thank you in advance

  2. wayneh


    Sep 9, 2010
    I'd try shorting across one or both of them, to see it they are really the problem. This will increase the voltage on the remaining LEDs, but only by 156/154. This is small and won't immediately change much. It's hard to say the best method for trying this. You might try a small piece of wire attached to both ends.

    If your testing succeeds, you can decide whether to replace those two or just leave it with two missing. It won't last forever either way.

    I'll add that this site struggles with this kind of repair. The topic of "LEDs connected to mains power" is forbidden for safety reasons, but the repair of commercial products is generally allowed. I'm not sure where the mods might go with this one.
  3. dl324

    Distinguished Member

    Mar 30, 2015
    I'd do more checking to determine how the LEDs are connected. The typical failure mode is for the LED to open. If the LEDs were all wired in series, the entire string would go out (plus it would be a bad design).

    If some LEDs were to fail short, it would either do nothing to the brightness of other LEDs (if driven from a constant current source), or make them brighter. Flickering would indicate some other problem.

    You can check individual diodes by applying a current limited voltage across the one you want to test.
  4. wayneh


    Sep 9, 2010
    @dl324 is right. Flickering is not explained by either an open or a shorted LED, and those are the two most likely failure modes. Something may be happening in the rest of the circuit.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    From what I've seen "flickering" happens when the sum of the forward voltage of the LEDs in the string is out of "output voltage" range of the constant current drivers specifications.. A LED failure could do that.. (but so could other reasons)
    wayneh likes this.
  6. absf

    Senior Member

    Dec 29, 2010
    Did you check the 2 electrolytic capacitors? Are they budging out?

    LED lamp.jpg
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Or just ditch that junk and go grab a Cree 4 flow from the hardware store (Home Depot,etc..) ..
    They are usually $4 or less.. I think I've picked some up for $1.97 during some "rebate" junk..

    Not even worth the time to crack it open..
  8. hp1729

    Well-Known Member

    Nov 23, 2015
    LEDs will show signs of aging before they fail completely. Perhaps the voltage across those two decreased as the LEDs aged, causing more current through it than others in parallel with it, increasing the aging process. Replacing those two LEDs puts them out of age with the rest of them in parallel. Removing them would be easier but may cause a shorter life of the others.
    I have some LED flashlights that are just batteries and LEDs,, no resistors. When one LED starts flashing I have found replacing all four gives better results. In your case that may not be much of an option.
    Remove the burned LEDs and expect others to follow eventually.
    Yes capacitors are always a common failure point, but that would effect all the LEDs, not just two.
    Last edited: Sep 8, 2016