I have noticed behind the screen that there is something that is like dirt. some times all over the screen and sometimes a part of it. ( when the backlit is on )
it does not interfere with the letters on the screen.
It looks as if it is inside the screen.
I have de-solder it and power it with external power supply and i have a photo of it.
If i apply force on the screen with my finger it seems to disappear.
If the force is removed it seems to appear again