Bypassing an LED

Discussion in 'General Electronics Chat' started by Outinthewoodsnf, Mar 28, 2015.

  1. Outinthewoodsnf

    Thread Starter New Member

    Mar 28, 2015
    2
    0
    Hi, I'm trying to fix my daughters TV, and I'm not trained in TV repair, or electronics for that matter..... However, I've traced it down to a burnt out LED in the backlighting.... There are 3 strips of 7 LED's, all wired in series... I don't have the funds to purchase the parts right now, and out of 21 LED's, I don't think losing one would be a big deal..... I'd like to solder a jumper in there, but I know that will decrease resistance and increase voltage, which is bad,,,, Could I solder a resistor or something in there, or will it get hot?, and if so, how do I know what resistance when my ohm meter will not read the good LED resistance?
     
  2. AfdhalAtiffTan

    Active Member

    Nov 20, 2010
    117
    11
    A picture would be nice...
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Try bridging it - if all the other LEDs in that series chain get brighter, the answers no.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    You are NOT trained in electronics or TV repair and you traced the problem down to ONE LED in the backlight??? Wow!

    The LED TVs I opened have a current controller inside. I would tend to believe bypassing one LED should not make a difference, the controller should decrease the duty cycle in order to maintain the current. You should also ask yourself why that LED burnt out in the first place. It seems to me that many of them are driven with currents way higher than necessary. You could try to lower the LED current too if you can find the shunt resistors.

    Anyway you may get more and better responses on the forum on badcaps.net, there are some real TV gurus there (I'm not one of them)
     
  5. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    The voltage across the 7 LEDs in series will go down if one of them is bypassed and the current will likely increase. Without knowing what the current is, it is impossible to say what size resistor you could use to bypass the LED.

    For example, 20 mA is a typical LED current. A typical LED voltage drop might be 2.5 Volts. The power in a resistor is I squared R.
    100 Ω ⇒ 40 mW
    1000 Ω ⇒400 mW
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Or put another way, 25mA across 100Ω will drop 2.5V. Worth a try if you have the resistors to test. Start with a 470Ω and move down. If 100Ω doesn't work, there is a different problem.
     
  7. Outinthewoodsnf

    Thread Starter New Member

    Mar 28, 2015
    2
    0
    I soldered in an LED from a Dewalt drill and hooked that strip to a 12 volt adaptor.... That one was way brighter, so I put a resistor I had in series with it..... They were all the same after that,,,,, Thanks everyone for your help.
     
Loading...