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.

Related articles:

Troubleshooting backlight failure.
Screen shows strange colors.
Troubleshooting video problems.

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248 Comments

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  1. 8
    cj2600 Says:

    Israelinkvm,

    I have a problem with a laptop, when I turn it on, the screen is very dark, with one very very soft image, at first, I think it was the lcd inverter, I’ve changed it with no success, the screen keeps black, I’ve read your post and followed the steps to test the inverter with another backlight, when I do this nothing happens, the lamp doesn’t turn on, what this could be??

    If the screen has no backlight and replacing the inverter with backlight lamp doesn’t help, apparently there is a problem with the motherboard.

    Also, this problem could be related to the video cable, but it’s not a common failure. If you have the lid close switch – a small button which turns off the light on the screen when you close the display, make sure this button moves freely. A dirty lid close button might get stuck inside the case and the laptop “thinks” that the display is closed even when it’s open.

  2. 7
    cj2600 Says:

    inquirer1,

    what should be the voltage settings for multimeter if I would test the inverter?

    When you test voltage coming to the inverter from the motherboard, you should set your voltmeter to test DC in the range somewhere between 0-50VDC.
    I think you should expect readings somewhere between 10VDC-20VDC, it depends on the model.
    You cannot use the voltmeter to test the AC output.

  3. 6
    cj2600 Says:

    chakra,

    I tested out the DC part of the inverter board, I was getting around 15V

    That means the inverter is getting power from the motherboard.

    but I tested the AC section of the board (the other end feeding the backlight) on a multi-meter and I did not get a reading.

    I don’t think that you can test the AC output with a multimeter, at least it never worked for me. I tried testing the AC output on a working laptop, just to find out what readings I should expect but as soon as I connect the multimeter, the backlight shuts off. That’s way I suggest testing a faulty laptop with another known good backlight lamp.

    So i could figure out that the inverter board was the problem. Replaced the inverter board and LCD screen lights up.

    I’m glad it worked for you.

  4. 5
    chakra Says:

    Hi,
    Thanks a zillion for this article. I had a dim LCD screen laptop. By following some of the instructions I could zero in on the problem. I tested out the DC part of the inverter board, I was getting around 15V, but I tested the AC section of the board (the other end feeding the backlight) on a multi-meter and I did not get a reading. So i could figure out that the inverter board was the problem. Replaced the inverter board and LCD screen lights up. Gave me a lot of satisfaction, kudos mate … great job of writing up the article in a very lucid manner.

  5. 4
    inquirer1 Says:

    hi,what should be the voltage settings for multimeter if I would test the inverter?thanks.

  6. 3
    Israelinkvm Says:

    Like I said before, I’ve tested with another backlight but it doesn’t light up, the brightness is ok. :(

  7. 2
    cj2600 Says:

    Israelinkvm,

    I have a problem with a laptop, when I turn it on, the screen is very dark, with one very very soft image

    Does it look like there is no backlight at all or it looks like the backlight works but the brightness is very low?

  8. 1
    Israelinkvm Says:

    Hi CJ.

    I love your blog, there’s a lot of tips that i’ve used to repair some laptop, thanks for that.

    I have a problem with a laptop, when I turn it on, the screen is very dark, with one very very soft image, at first, I think it was the lcd inverter, I’ve changed it with no success, the screen keeps black, I’ve read your post and followed the steps to test the inverter with another backlight, when I do this nothing happens, the lamp doesn’t turn on, what this could be??, maybe the motherboard isn’t sending power to the inverter to turn on the lamp??please, I need your help. Thanks.

    Note: When I plug an external monitor there’s no problem, video is ok.

    P.S. Sorry for my english :(

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