Help diagnosing LCD Backlight

Discussion in 'General Electronics Chat' started by Litch, Jul 14, 2013.

  1. Litch

    Thread Starter Member

    Jan 25, 2013
    86
    7
    The in-law's shop security screen "just went dead" the other day.

    It's an embedded system with a 10" screen, 4CH cameras.

    http://www.jaycar.com.au/productView.asp?ID=QV3030

    I'm not sure how to diagnose the backlight (as that's what I believe has gone wrong here).

    JPG attached is the backlight part of the circuit, I'm just after:

    I really have no idea where to start - I have a multimeter - but I assume the backlight (CCFL) is going to be around the 1 to 15KV, therefore there's no "quick" measure to see if the output is normal...

    Any hints?
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    A quick glance shows R122 at the bottom looks very heat damaged.

    You could remove it and check its resistance.

    Another big cause of CFL driver faults is bad electros, I would just replace those 3 electros next to the inductors. You need to replace them with 105'C low-ESR types.
     
    Litch likes this.
  3. Litch

    Thread Starter Member

    Jan 25, 2013
    86
    7
    Thanks RB - exactly the advice I was after!
     
  4. Litch

    Thread Starter Member

    Jan 25, 2013
    86
    7
    I pulled the LCD apart and extracted the backlight, looked up the model number - It's an LED backlight; runs off 200mA @ 9V...

    /facepalm

    That simplifies things a lot.
     
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