It should be a DC voltage so set the multimeter to DC Volts (start on the 200V scale - it won't be anywhere near this value at all but it is always safer to start high and then lower the scale to get a more accurate measure) and then connect the meter between an earth point on the motherboard and one of the pins.
Be careful not to "bridge" the meter's test probe across two pins and short them out as you may damage something.
Here’s an image from a different laptop that shows what I mean. (sorry that it is a bit small)
Even though it is a 40 pin connector the principle is the same. LED power (VDD LED) is always there on pins 1, 2 & 3 whilst the backlight on (BKLTON) lead is connected to pin 4.
Again this schematic is not the one for your laptop. It is only to show how it might be wired, so the pin connections might not be the same. It is unfortunate that you can’t find the make and model number of the panel to get the datasheet to make it easier. Did you try searching for the motherboard schematics using the motherboard’s board number at all?
(click on image to enlarge for better viewing)
If there is no constant LED power on any of the pins as you say there is a problem with the LED power supply on the motherboard.
If there is LED power available then it may be a problem with the backlight on circuit, either on the motherboard or in the panel or the LED power circuit in the panel.
That is of course if it is wired like this and I don’t know if it is or not.
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I see that you had not uploaded another side of the mainboard.
what had you checked?
Yes because the backlight fuse should be around the display port
where it's written EDP it's the display port
Don't know the answer but check if there is voltage is on EDP connector pins 27-30. (Not sure of this but maybe worth a check)
If there is, it may not be a power supply problem as such, it might be a BL_On problem.
With some laptops the backlight power is available all the time to the panel and a signal is sent to the panel to switch it on and off. The actual backlight power supply is not turned on and off on the motherboard
Just so that you're aware of this possibility and don't spend all your time looking for a fuse that may not be the problem.
If you know or can find out the model number of the LCD panel, look for the LCD panel data sheet as this will have the pinout for the cable connection.
If you're lucky the panel make and model number is sometimes found on the back of the panel itself.
Alternatively look for the motherboard schematic by searching online for the "motherboard 'board number' schematic"
Just a thought. Hopefully it doesn't sidetrack you too much if it is not the case with your laptop
Jayeff, thank you for your answer, unfortunately I can't access to the panel LCD because there are bezel cover and metal cover on the back. Sorry but where is the pin 37-40 ? can you show me on my picture please ? Antonin G
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