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TCL 55US57 backlights, no picture.

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    TCL 55US57 backlights, no picture.

    So here we go with another screen short TCL. For this exercise left and right will be reference looking at the screen.

    The person I got this TV from said the color was bad in a vertical fashion about 1/4 of the way over the left side of the screen. Shortly after the symptoms below started.

    Power Supply, main and T-CON board are working.

    Symptoms: The TV has backlights but no picture with both FFC's attached to the T-CON and does not respond to the remote or buttons, and the TV appears to continuously re-boot.

    Unhook FFC from left side of the T-CON and I get half a picture upon the right side, sound, response to remote and buttons but no picture upon the left side. The left 10% of the screen has a rainbow appearance, from there the screen is dark to the left 25% of the screen and white on the rest of the left side to the centerline.

    While the right side has a picture, from the centerline the right 50% of the picture is darker then the rest of the right side of the screen. This appears to indicate the short on the left side of the screen is affecting the right side of the screen.

    As seen in picture #2, if I use the tape cut-off method on the terminals in the yellow box and attach both FFC's to the T-CON the TV will turn on with a picture on the right and a black screen on the left.

    None of the capacitors upon the left side source driver board appear to be short.

    Test point VGH shows 135 ohms resistance to chassis

    See pictures 3, 4 and 5. Several resistors upon the left source driver board indicate short. They are too small to see a value printed upon them.

    Ordinarily I'd start plucking resistors off the board until the short disappears but before I do I'd like to see if anyone thinks I've missed anything (like a bad COF tab) or if there's further testing I should do? I'm inclined to start with the resistor bank where the previous owner saw the discoloration on the screen near the third COF tab from the left.

    NOTE: The last 2 pictures are with the TV upside down
    Attached Files
    Last edited by DXseekerMO; 09-18-2021, 04:05 PM.
    They call me......."threadkiller"

    #2
    Re: TCL 55US57 backlights, no picture.

    what the heck happen in picture 5 to the tab bond area... it looks damaged from some sort of rubbing event? There are lots of labelled voltages "points" on the boards... are they similar for each side of the panel? "dry resistance measurements" (ie not powered) might confirm some more of what you have done in terms of locating bad "tracks" associated with the tab(s).

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      #3
      Re: TCL 55US57 backlights, no picture.

      Originally posted by budwich View Post
      what the heck happen in picture 5 to the tab bond area... it looks damaged from some sort of rubbing event? There are lots of labelled voltages "points" on the boards... are they similar for each side of the panel? "dry resistance measurements" (ie not powered) might confirm some more of what you have done in terms of locating bad "tracks" associated with the tab(s).
      I'm pretty sure that's an artifact of photography, in-person there is no damage to the tab bonds I can see. I saw that in the picture after I took it which made me check it before I posted.
      They call me......."threadkiller"

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