How to Test LCD Inverter Power

If you have a LCD monitor with a dark or dimly lit display screen, the most likely reason for the problem is a defective inverter board. The LCD inverter board supplies power to the backlight bulb, which in turn illuminates the LCD screen. A dim LCD screen is usually the result of an inverter board's failure to provide sufficient power to the backlight. On rare occasions, the inverter board itself might not receive sufficient electrical current from the power supply. Testing the power and voltage on an LCD inverter is easy and quick.

Power off the LCD monitor and remove the AC adaptor.

Remove the rubber grommets from the outside edge of the LCD monitor bezel with an awl or other sharp object (note: depending on the LCD monitor, the rubber grommets might be on the front or rear face of the monitor screen bezel).

Remove the screws that secure the front and rear bezel pieces of the monitor with a Phillips screwdriver. Separate the two pieces of the monitor screen bezel and remove the front bezel piece from the monitor.

Disconnect the backlight lamp from the right side of the inverter board (located at either the top or bottom of the LCD monitor display screen).

Plug in the AC adaptor and power on the LCD monitor.

Adjust the dial on the multimeter so it is set to display voltage measurements. Place the red probe lead (positive) on the solder pin labelled "P1" or "F1" next to the cable connector that runs from the main circuit board inside the monitor. Place the black probe lead (negative) on the ground trace receptacle located around the inverter board retaining screws.

Look at the voltage display reading on the multimeter. The voltage from the main circuit board to the LCD inverter should be in the 12 to 20 volt range. If the voltage going into the inverter board is lower than 12 volts, the main circuit board can not supply enough voltage to the inverter.

Disconnect the backlight lamp from the inverter board.

Plug the extra backlight lamp into the connector receptacle on the inverter. If the backlight lamp lights up, the inverter board is functioning properly. If the new backlight lamp does not light up, you must replace the inverter to repair the LCD screen.


You must be very careful when testing the power and voltage for the inverter. If you touch the wrong solder lead, you might short out and damage the LCD monitor screen.

Things You'll Need

  • Multimeter
  • Awl
  • Phillips #1 screwdriver
  • Flathead screwdriver
  • A working backlight bulb
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About the Author

Jeff Grundy has been writing computer-related articles and tutorials since 1995. Since that time, Grundy has written many guides to using various applications that are published on numerous how-to and tutorial sites. Born and raised in South Georgia, Grundy holds a Master of Science degree in mathematics from the Georgia Institute of Technology.