If your LCD TV's display screen is dark or difficult to see, the problem is usually a result of either a defective backlight lamp or LCD inverter board. Modern backlight lamps seldom fail; therefore, in most cases, the issue is with the TV's LCD inverter board.
Problems with LCD inverter boards often result because of a lack of power that prevents adequate current from passing to the backlight bulb. If you are handy with some basic electrical tools, you can test output from the LCD inverter to the backlight bulb to determine if the inverter is defective.
Power off the TV and disconnect the AC adaptor.
Remove the plastic or rubber covers or grommets from the outside edge of the TV screen bezel with an awl or other sharp object. Depending on the television, the cover may be on the front or rear face of the TV screen bezel.
Remove the retaining screws that secure the bezel piece of the television with a Phillips screwdriver. Gently pry the bezel from the TV casing, then remove it and set it aside.
Unplug the backlight connector from the right side of the TV's LCD inverter board, located at either the top or the bottom edge of the LCD TV display screen.
Reconnect the AC power adaptor to the TV, then turn on the LCD television.
Set the multimeter so that it displays voltage measurements. Connect or touch the red probe (positive) to the pin labelled "P1" or "F1" beside the cable connector that leads from the TV's main circuit to the inverter board. Connect or touch the black probe (negative) to one of the ground trace receptacles around the inverter board retaining screws.
Review the voltage reading on the multimeter display screen. The voltage that passes from the main circuit board to the inverter board should be between 12 to 20 volts. If the voltage is lower than 12 volts, the main circuit board is not supplying enough voltage to the inverter. In this case, the circuit board or power transformer may be defective.
Disconnect the backlight lamp from the LCD TV's inverter board, then connect the extra backlight bulb to the connector on the inverter. If the backlight bulb lights up, the TV inverter board is OK. If the new backlight bulb fails to light up, you must replace the inverter board to repair the television.
Exercise caution when testing the power and voltage for the TV inverter board. If you touch the wrong solder point on the inverter or circuit board, you will short out and damage the LCD television.