How to Recognize a Bad LCD Backlight
LCD displays in laptops and monitors are illuminated by a fluorescent backlight. If the backlight fails it can exhibit some odd symptoms along the way. Pink displays, fading or dimming, and faint, unilluminated screen images can all indicate that it's time to replace the display backlight. Before making the repair, of course, rule out other factors such as software and loose connectors that could result in a display that doesn't work or doesn't look right.
Pink Displays and Other Failure Modes
One of the most common backlight failure symptoms is the "pink display." This shows decay in the backlight element which leads to failure. The screen color may improve after initial turn-on. A screen that's dimmer than usual, or dimmer in the corners only is also a likely indicator of a progressive backlight problem. If the screen is completely dark and did not go through a progressive failure, it may require some diagnosis to determine the cause of the problem
Display Card and Cabling Failures
The part of the computer which generates display images, often called the display card though it can be integrated with the motherboard, can produce problems similar to backlight issues. The associated cabling internal to the laptop or between the computer and LCD display can create image problems which usually appear either completely black or more complex in nature than dimming, such as a "fractured" or "torn" appearance due to problems with timing signals.
Backlight Power and Software Control
The operating system can control backlight levels. Many laptops have function keys programmed to raise or lower the screen brightness through software. Brightness problems related to software can also be the result of power saving settings on laptops and faulty or corrupted display driver software. If the problem doesn't occur when the computer startup is paused (by pressing the correct function key) at the boot options screen before the operating system boots, that indicates a likely software problem.
Some problems related to display brightness may have multiple causes. A dark screen with images faintly visible can have multiple origins including LCD backlight failure, backlight "inverter" failure, or a dimming problem. A completely dark screen could be anything from basic power supply problems to cabling. A display which illuminates for only a few seconds or minutes may be related to monitor power circuitry, a bad backlight, inverter or LCD display.
Diagnosis of LCD Display Problems
Symptoms such as a pink display which are typical of backlight failure provide an easy diagnosis of the problem. A display over five years old is more likely to have a failing backlight. An LCD monitor can be moved to another computer for comparison, or the computer can be stopped during boot at the BIOS configuration screen to rule out operating system problems. Connector and power problems in laptops may be associated with past repairs, dropping of the device or carrying it by the screen placing stress on the cables passing through the hinges.