1) Wrong LCD screen
2) Video Cable (LCD Cable) is not connected tightly.
Motherboard side, or LCD screen side; or both.
3) IF, a screen Inverter is used, the small cable from the Video Cable, that connects to the screen Inverter; is not connected, or has a loose connection to it. (screen Inverter)
4) An LCD screen, and a screen Inverter are a Matched unit.
If it's the wrong LCD screen......................?
5) IF, a screen Inverter is used; the diagnosis was wrong, and the LCD screen was replaced.
90 PERCENT of the time, the fault is a bad screen Inverter.
A) Laptop's LCD screen uses a CCFL, (Or more than one), for a Backlight; the laptop uses a screen Inverter.
Diagnostic flowchart leads from Graphics Chipset, to Video Cable, to screen Inverter, THEN, LCD screen.
Expensive LCD screen was replaced, instead of the actual part that needed replacing;
Video Cable: $9 to $22
Screen Inverter: $9 to $22
LCD screen: $60 to $245
B) Laptop's LCD screen uses LED backlighting, and does NOT use a screen Inverter:
Diagnostic flowchart is;
A) Video Cable;
A Video Cable should have it's connections PHYSICALLY checked.
You have to try to push the connectors in tighter.
Visual inspection alone will NOT do.
Making sure the Video Cable connections are tight, and this does not fix the problem, then the Video Cable needs to be removed; and every wire in the Video Cable checked for Continuity with a multimeter set to OHM's. (1K)
Not feasible, then take the Video Cable down to the nearest small computer shop; and have the resident tech check it for Continuity.
Should only be a few bucks.
Or just replace the Video Cable.
(Parts changing I know, but...........?)
An LCD screen cannot produce light. It needs an additional light source.
A Backlight is the additional light source.
A Backlight can be a CCFL, (Or more than one), or a series of LED's.
(Light Emitting Diode)
A CCFL is a Cold Cathode Fluorescent Lamp. (Bulb)
Similar to Fluorescent lighting used in homes, and businesses; but on a MUCH smaller scale.
Average thickness is 2mm. That is a little large than 1/16th of an Inch.
Average thickness is almost as long, as the LCD screen is in height.
View the last 8 photos,http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp/
A screen Inverter is used to convert the power, (Electricity), from the laptop; for the LCD screen, and Backlight.
As previously stated, Backlighting that uses CCFL, uses a screen Inverter.
LED backlighting MAY, or MAY NOT use a screen Inverter.
When the LED backlight technology first came out, it seems some did use a screen Inverter.
It also seems as the technology advanced, LED backlighting does Not use a screen Inverter.