How to test screen inverter
In this post I explain how I test the inverter board in a laptop.
The inverter failure is very similar to the backlight lamp failure. In both cases the screen gets very dark and the image becomes very faint, barely visible under a bright light.
There is only one reliable way to test the inverter – replacing it with another one and see if the screen lights up after that.
Alternatively, you can connect a new backlight lamp and see if your presumably bad inverter lights it up.
In most cases I go with the second method – using my test backlight lamp. Why? Because the same backlight lamp will work with many different inverters as long as they have matching connectors.
Usually the inverter is mounted inside the display panel below the screen. In most cases you can access it after you remove the display bezel. The inverter has connectors on both ends. The left side connects to the LCD cable. The right side connects to the backlight lamp which is mounted inside the screen. Check out this display diagram.
To make sure that inverter gets power from the motherboard (via the LCD cable), you can test it with a voltmeter. In my case I connected the “+” lead of the voltmeter to the pin 1 and the “-” lead to the ground trace around the screw hole. I got about 19.4V DC on that side of the board, so it’s getting power from the motherboard.
WARNING! If you accidentally short something on the inverter while testing, you can damage it. Proceed on your own risk! Not sure? Don’t do that!
So far we know the inverter is getting power from the motherboard, but the screen still has no light. Apparently, it’s either bad inverter or failed backlight lamp.
Now let’s test it with a known good backlight lamp.
1. Unplug the screen backlight cable from the right side of the inverter.
2. Connect a known good backlight lamp.
Turn on the laptop.
1. If the test backlight turns on, the lamp inside the screen is bad. In this case you’ll have to replace the screen. Also, you can replace the backligth lamp which is not easy and not recommended.
2. If the test backlight doesn’t turn on, most likely we have inverter failure. Replace it and test the laptop again.
There are two different types of backlight connector, you can see them on the picture below. The top one (big) is not as common as the bottom one (small). I mostly use lamps with a small connector.
IMPORTANT! When you buy a new lamp for test, make sure the connector fits your inverter.
On the following picture you see how I’m testing the laptop with a new lamp.
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