Help 42lf651 suspect backlight fault

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Rickig
    Senior Member
    • Mar 2015
    • 112
    • England

    #1

    Help 42lf651 suspect backlight fault

    Hi all
    I have acquired this set 42lf561 that was sold to me has having a duff bavklight
    However when powering on the set it looks as the the back light is on but dim. (All the others I've fixed you'd struggle to see the image, this one not so) see pic.

    Before I start stripping down the set just wondering if anyone has had a similar issue
    and point me in the right direction

    Thanks
    Attached Files
  • dick_barton
    Badcaps Legend
    • Aug 2015
    • 6642
    • Wales

    #2
    Re: Help 42lf651 suspect backlight fault

    Have the backlights in the menu been turned to far down?

    If you could post pictures of the circuit boards and how they interconnect would be useful.

    I would start by measuring the led voltages at the connector since the set is working but backlight dim. It could also be the dimming level set low.
    Willing to help but I'm no expert.

    Comment

    • Andrew F. Ali
      Badcaps Legend
      • Jan 2014
      • 2450
      • Trinidad & Tobago

      #3
      Re: Help 42lf651 suspect backlight fault

      Backlights seem to be working but at low voltage. I am not certain if there is a high resistance that developed in the LED Driver circuit or if just a few strings in the LED array are working and some off. The only way to tell IMO is to open up the Panel and use a LED Tester to power-test each string.

      Comment

      Related Topics

      Collapse

      • howardc64
        Samsung QN75Q6FNA backlight no display, red LED blink 2x, fault in panel
        by howardc64
        • Prior owner tried a replacement main board. No difference.
        • Samsung 2x red blinking standby LED = panel fault
        • Jumpered FB_TRDY_1 (pin 1 CN1300 left. main tcon->left side buffer boards) and FB_TRDY_3 (pin 95 CN1301 right. main tcon->right side buffer boards) This allows testing individual T-Con (on main board) connection to panel on this Samsung. Found fault on left side (viewing from rear of TV)
        • Each side has 2 buffer boards, disconnected left side flex between 2 buffer boards. Fault is on the left most board.
        • Tape masking eventually isolated to CN1300 pin 15 (CKV4_GOA) Display
        ...
        Yesterday, 10:54 PM
      • DanPoka
        Guide me through repairing a Dell p2210f LCD ccfl backlight monitor
        by DanPoka
        I bought this p2210f dell monitor to fix. Schematic is the same as p2210.
        Behaviour is that monitors comes on but then backlight switches off almost instantly. If I look with flashlight I can still find the "No signal message". So definitely a backlight issue. Trying to advance the issue I proved that the protection circuit is switching off the backlight by shorting out C3 and resistor to disable the INL chip then re enable by removing the short.
        This is where it gets interesting. When I disassembled the monitor to solder leads on c3 capacitor I noticed the backlight flickered...
        02-15-2025, 05:05 AM
      • Comp_Pro
        No Backlight Macbook A1990 820-01041
        by Comp_Pro
        Hello all,

        Am trying to figure out this backlight issue with this A1990 Macbook Pro.

        Tests performed:

        There is no backlight even with a good screen.
        Backlight IC is receiving the correct support voltages.
        Fuse F8400 ok
        Current sense resistor R8400 ok
        Backlight IC is receiving 3.3V on enable pin.
        Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
        Backlight IC receiving 5V from PP5V_G3S
        Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
        I2C_BKLT_SCL and I2C_BKLT_SDA both measure...
        05-06-2024, 10:23 PM
      • cheebster
        iPad Pro 12.9 5th Gen Backlight Issue
        by cheebster
        Hello, got an iPad Pro A2378 12.9 5th gen with no backlight. Got another test unit without screen, tested the screen, still no backlight with the test unit.
        Figured out the backlight on the screen was bad, ordred a new backlight from mobilesentrix, *carefully replaced it* without damaging the lcd, oh well.
        Final result, issue is still there, the screen has no back lights. So i'm back to square one, with 3 hours less and 100$ out, issue still on the screen.
        The panel is still ok, i can see the apple in the middle of the screen when it kicks in, just no backlight.
        Anyone...
        05-20-2025, 09:17 AM
      • triplefour
        TCL 75S421 has sound but no backlight not even a flash
        by triplefour
        TCL 75S421
        PSU BOARD: 40-L402H8-PWD1CG
        it shows not even a flash of backlight when powering up.
        but the tv appeas to turn on and i can hear the sound of the menus moving and clicking. i can power down the tv with the button.
        testing the backlights with my tester all 4 strings lit up and showed similar voltage drops. around 110 or so.
        unplug mb and leave only psu plugged into backlights (PSU + BL SELF TEST MODE?) does not light the backlights.
        i do see 24v but 0v on PSON and BLON (i didnt write this down tho so cant be sure)
        with mb connected, PSON...
        11-17-2023, 09:54 PM
      • Loading...
      • No more items.
      Working...