LCD Backlight Replacement - How To Test If The Backlight Lamp Is Working If you are installing a new LCD backlight in your laptop and want to test if it is working, there are 2 ways to do so:
1. Connect the replacement bulb to the inverter board and turn on the laptop. The bulb should turn on.
2. If it doesn't, then connect the video cable to the LCD screen before turning on the laptop. This should light up the backlight bulb. Source Website http://LCDMonitorRepair.annics.com