No backlight LED Screens Part 2
Usually when you want to find what is the problem with this faulty type you will have to use a lot knowledge.
There are many possibilities when you don’t have any backlight, let’s list them.
Cable , screen, motherboard near connector or fuses, video card or my favorite water spillage with rust.
1.Checking the cable can be done in 3 ways or verify.
The first and the simple way is to change the cable and see if you backlight its back.
Checking the cable can be done manually with a multimeter.I personaly i do that ,if its the last resort, if i don’t have another alternative.
2.When the screen its bad usually you can change it, but this is the faulty with the smallest probability to happen.
If the scre actually is bad the there are 2 possibility : the fuse is bad or the if that handle everything for then screen its bad or burn. I saw cases! Its not worth to fix.
3.OK! Motherboard not providing power for the screen. Just a second I’m checking for space because here I can write all day 🙂 .
I’ll start with some basic reading from a laptop schematic.
3vlcd, 3v, BL_ON, vadj,lcdvdd,etc
Usually when you check for those voltage on the connector you will need to find max 3 types of voltage : 3.3, 3 and 12v.
When you don’t find them you can take them from another side.
There are few notebooks that don’t have a fuse and you need to find what wrong.
If the voltage is there that means its the cable but be sure to test it with another screen.
My last repair was on a HP CQ71 and the notebook was missing the adjust voltage, you brightness on the screen, with vadj1 signification on the schematic.
There was 2 option to find the 3.3 v adjustable .
3.3v means 100% brightness and I think 3 or 3.1 v minim on brightness.
The second and my favorite its to connected direct to a stable 3.3v with a jumper(wire).
4. When it comes to video repair in a notebook that’s bad.
There are many videos online how reflow .
I saw many notebooks that had problems with backlight because of the GPU.
For me the number one with no backlight its dell , that GPU tend to fail a lot.
5. Corrosion in a notebook its biggest enemy with dust.
Last notebook with that problem was a HP 6930p elitebook.
I don’t know what happen but I saw the motherboard had met the water super serious.
In this case a coil that provided the main voltage for the screen was missing, with B+ signification. The problem was not that simple Because the coil was fried and it was not the only component bad. Near the connector there where 2 capacitors that was shorted.
Because I was in a rush I just remove them and supply the voltage from the coil pad to B+ so the screen will have backlight.
When you bypass the voltage you will not be able to use the brightness function, it just depends on what problem you encounter.
If have any questions please tell me because I will be glad to help with any problems related to this type of faulty.
Be safe and good luck.