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Many times customers deliver notebooks with a black screen and we are not sure just by looking if the problem is in the inverter, flat cable, LCD lamp or the motherboard itself, we always have to open the device for testing.

This is a method to verify if the high voltage needed to start the LCD lamp is being provided by the inverter. If high tension exists and yet the screen does not light up the problem can be only the lamp. You can discard other possibilities and save your precious time. I've been using this method a few years and never it failed me.

You will need a good multimeter with frequency measurement function. Set the multimeter in the frequency range (Hertz - Hz) and touch one probe (only one) on the LCD frame, near the region the LCD lamp is connected.

If there is high tension, your meter will show between 50 and 60 kHz, otherwise will display 0 or around 50 to 60 Hz due to some interference.

In the video below, you will notice that while the notebook LCD light is turned on, an interference of approximately 60 Hz occurs since my multimeter is very close to the screen. When the lamp is off, the display goes to 0.

This test only works for LCDs with CCFL lamps, it does not work for LCDs with LED illumination. Hope this helps you.