lg 26LC2R lcd tv backlight turns off

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  • Ridje
    New Member
    • Apr 2023
    • 4
    • Slovenia
    #41
    Re: lg 26LC2R lcd tv backlight turns off

    My TV has exactly the same problem - backlight gets turned off after few seconds. Measuring the voltage on pin 1 on OZ9936 i got:
    - a the start - 0volts
    - soon after start, the backlight turns on - 1,95volts
    - after cca 2 secs - 0volts again, backlight off
    Datasheet says pin 1 is the enable pin - but where does it get the enable signal from? Why does this device stop providing enable signal?
    I tried injecting 1,5V in the attached pin1, but the backlight remained unstable, the device sinking enable signal to ground was "fighting for control". Anybody traced down where does the enable signal come from? I would do as others suggest of providing fixed enable signal from the power pin directly, but it would be even better to figure out why does the enable signal sink and repair this.
    Also, being mostly in tube amps and certainly THT stuff: OZ9936 is a SMD part; how do I lift a single pin off it - if I melt the solder on the pin and wedge sometihng under it, will it lift? Is it risky that I break it off? Wouldn't it be better to interrupt the trace somewhere and install power providing circuitry there?

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      • Ridje
        New Member
        • Apr 2023
        • 4
        • Slovenia
        #42
        Re: lg 26LC2R lcd tv backlight turns off

        Doing some "continuity poking" around the PCB I found out the signal to pin 1 of OZ9936 comes from the IC named U11, which is a BA10393 comparator - I would have to further investigate, what occurs on pins 2 (-) and 3(+) of the comparator. (Log to self and whomever: comparator outputs full on if the positive is higher than negative and zero if negative is higher than positive) And where those pins 2 and 3 are connected. It is probably safe to say it would suffice to ground pin 2 to save this whole drama, but I must test this idea (or can by any chance pin 3 be negative?), Plus, the device sunk to ground through pin 2 might not like it. Any thoughts?

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          • Ridje
            New Member
            • Apr 2023
            • 4
            • Slovenia
            #43
            Re: lg 26LC2R lcd tv backlight turns off

            Abandoned all this U11 stuff as overkill and just lifted pin 1 of U11 from the board, then injected 2V to pin 1 of BA10393 IC - but the problem persists. Reading the datasheet (pg. 5, point 8) tells this: "Toggling the enable signal from low to
            floating will resume normal operation." What could that mean? Should I put a momentary switch to the back of the device? Or just scrap this old box?

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