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LCD backlight control with M.NT68676.2A LED controller board

Discussion in 'LEDs and Optoelectronics' started by fggf, Nov 4, 2017.

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  1. fggf


    Nov 4, 2017
    Hi this is my first post so apologies if I do something wrong.

    My electronics skills are pretty basic. I can solder and use a multimeter.

    I'm using a M.NT68676.2A LED Screen Controller Board to control a panel from a broken laptop. It was easy to set up and works very nicely. I bought it from this eBay listing which shows exactly what I got:

    There's a spec sheet for it here:

    My problem is that there is no way of setting the backlight through the menu. To be clear I don't mean brightness or any other image settings but specifically the backlight power (I'm trying to save energy as I run everything off solar power).

    When the LCD was installed in the laptop I was able to control the backlight using hardware buttons built into the laptop so I know the panel has the capability.

    The nearest thing I have to a clue is that the spec sheet mentions an inverter connector pin No.4, ADJ, which says "Brightness Adjustment for Panel". But using the kit as provided the included connector leaves this pin (and only this pin) unconnected.

    I've tried talking with the eBay seller, he's done his best to be helpful but either only has basic knowledge or we may be having communication/language issues.

    I've spent a fair bit of time Googling this but had no luck so far. Can anybody offer any help please? Thanks
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Welcome to EP.

    Brightness is proportional to power consumption as the backlight will need more power for brighter backlight.
  3. fggf


    Nov 4, 2017

    When you set 'brightness' in the menu of the monitor or through graphics drivers etc it doesn't affect power, it just mixes the colours differently so that they appear darker. OLED screens and CRT monitors use less power for darker colours but with an LCD panel the backlight power usage remains constant unless you adjust it specifically.

    'Brightness' (as used in these menu settings) is an RGB change, 'backlight' changes the power going to the backlight bulbs (through PWM I believe).
  4. kellys_eye


    Jun 25, 2010
    Not really - they actually DO control the brightness of the backlight which you can clearly observe if your screen power saver is set and you observe the brilliance slowly decreasing to 'off'.

    That controller board shows CN5 pin 4 as labelled for backlight control - presumably requiring a PWM signal (pulling low) to modulate the brightness. Unless you can find some more specific information you might need to experiment a bit - a simple 555 astable with variable pulse width/frequency to begin with.

    It might even be as simple as a potentiometer! Without more details we're in the dark here....

    Usually you need to be quite specific with such modulation methods to avoid moire patterns that can occur if the PWM frequency is any multiple of the dot frequency.


    The board you got can also be delivered with an LCD backlight control board

    seems like you opted for the 'cheap' version.......
    Last edited: Nov 4, 2017
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