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Disable backlight of LCD monitor

Discussion in 'Troubleshooting and Repair' started by Agnosticus, Aug 14, 2017.

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  1. Agnosticus

    Agnosticus

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    Aug 14, 2017
    Hi everyone,

    Sorry, I wasn't exactly sure where to put this post, as I'm not exactly doing repairs. Anyway, what I want to do is disable the backlight on my LCD monitor, because I have sensitive eyes. I know that the monitor is still usable in natural daylight (there's a YouTube video where one guy has done this, but I'm not clear on exactly how and he won't respond to my posts on his channel).

    So I've disassembled the monitor and found the cables which connect the lamps to the circuitry. When I disconnect one or more of the cables from the circuitry, the monitor stays on for a moment then switches off. So obviously the circuitry detects when one of the cables is disconnected and shuts the monitor off. Basically I want to trick the circuitry into believing that the cables are still connected or that a current is running through the lamps to the circuitry. Or maybe there's another way I can do this? I just want a backlight free monitor!

    Any help muchly appreciated from me and my eyes!

    Cheers,

    Agnosticus
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You might be able to get away with replacing the backlight with a resistor that will draw approximately the same power as the backlight.

    Is it a CCFL or a LED backlight?
     
    Agnosticus likes this.
  3. Bluejets

    Bluejets

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    Oct 5, 2014
    I thought it was only the inverter that shuts down on fault.
     
    Agnosticus and HellasTechn like this.
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Are you totally sure you can see your monitor without a backlight? I've repaired many laptops that have had backlight failure and the owners have sworn the 'display is dead' as they can't see anything at all!

    Most laptops/monitors I've seen/used have been able to dim considerably enough to avoid hurting the eyes and the addition of ambient lighting from 'behind' (the user) also help.

    If you can 'see' in daylight you should be able to adjust your display and environment to suit.
     
    Agnosticus likes this.
  5. Agnosticus

    Agnosticus

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    1
    Aug 14, 2017
    Hi everyone,

    Thanks a lot for your replies. The guy on YouTube replied to me. Yes, it is possible:



    In his case I believe he has detached the light from the monitor but not disconnected it from the circuitry. It's LED backlit. It doesn't matter how dim the light is, I still get headaches. I don't want to get into a discussion about this as I find it's a waste of time - nothing gets resolved. If I can achieve what the guy above has achieved I know I'll be better off.

    Maybe there's a way I can substitute a resistor or resistors for the backlight...
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    He doesn't show the rear of the display. You can get that effect by removing not only the back light but also the covers over the back of the display panel itself such that ambient light passes through from rear to front. This is why his display is 'disassembled' ......

    With the covers still in place, no back light = no picture.

    The Youtube video is misleading.
     
    davenn, Agnosticus and HellasTechn like this.
  7. HellasTechn

    HellasTechn

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    Apr 14, 2013
    That is exactly what he did. he is using the LCD without its case or the reflectors on its back.

    Removing the LED backlight should not affect the LCD display. In other words picture should be displayed on the LCD no matter if the backlight is connected or not.

    Ofcource you could always leave the led's conected and wraped with insulating tape so you will no longer see the light. Not to mention that you have to exercise extreme caution when removing the LCD from it housing because the panel is very fragile and wires going from the Tconboard to the crystal are thin as hair and if damaged then the LCD is useless.

    P.S.

    It is not exactly the natural light that makes the image visible. Notice the blue lamp right next to the LCD panel
     
    Last edited: Aug 15, 2017
    Agnosticus likes this.
  8. Bluejets

    Bluejets

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    Oct 5, 2014
    That was my thoughts also in #3.
     
    Agnosticus likes this.
  9. Agnosticus

    Agnosticus

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    Aug 14, 2017
    Thanks heaps for your replies, guys. Sorry for the long delay replying.

    He said that he threw away the backlight.

    I found four connectors at the back which control the backlight. When I disconnect them the LCD display is not visible. I'm sure there's a censor in the circuitry which disables the display when there's no backlight. The guy in the YouTube video thinks that the display should be visible even without the reflector at the back - i.e. without a backlight or natural light through the screen.

    Maybe I'll try wrapping the LEDs in insulating tape? Wouldn't the tape get too hot from the light?

     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Measure the voltage across the LEDs when operating, and then the current through them.

    From this you can calculate a resistor which will appear to the monitor to be the equivalent of the LEDs.
     
    Agnosticus likes this.
  11. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Very, very vaguely.....

    I've repaired many laptops where the owner swears blind that the screen is 'dud' (because the backlight has gone off and they can't see 'anything') but if you hold a torch at an angle to the screen you CAN see an image. It's almost.... almost invisible if the backlight is off though.

    You will NOT see the screen unless you remove the rear reflective (opaque) screens.

    I know of no laptop or screen that switches the video off if the backlight stops working (or is disabled) - well, never come across one anyway.....
     
    Agnosticus likes this.
  12. Agnosticus

    Agnosticus

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    Aug 14, 2017
    I know this is a belated reply, but thanks for your messages. I still haven't tested this out but I suspect the image is still there, but not visible. I don't think it would help much . I just have really sensitive eyes and a particular eye condition (pigment dispersion syndrome) which makes all reading tedious - in particular reading off a screen.

    Cheers.
     
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    and that is where you were being led astray by the video, he is wrong, as @kellys_eye stated a couple of times

    I also have/still do work(ed) on many LCD monitors and panels .... you will see next to nothing without some sort of back lighting

    Dave
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    And you'll still see nothing if you've removed the polarising film(s).
     
    davenn likes this.
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