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. 58
    waligi Says:

    Hi everyone,really need help with my compaq MA8.
    when turned on,nothing appears on the screen and the touchpad lights up only for a few seconds and then goes back off.After that,nothing happens and any key combination given does not even give the usual beeps after.
    I would appreciate any suggestions,thanks

  2. 57
    Jesse Says:

    Could the bulb and the inverter board go bad at the same time?
    I sent the new inverter board back and ordered a new LCD screen. When I put the new screen in it’s still dark! I’m guessing they were both bad and now I’ve got to reorder the inverter board…

    Thanks for your help!

  3. 56
    Stefan Says:

    I have a similar problem with my Desktop LCD, a LCD Flatron W2242T.
    The bottom half of my screen is dark and has light spots right at the bottom, whereas the top half works perfectly. I was considering buying a new screen which wud set me back $300 = =”
    but this site has given me hope, maybe i have a faulty backlight at the bottom. Any advice on what i should do?
    thanks guys

  4. 55
    catalin81x Says:

    Hi, I have a problem with a laptop, Dell D830 when I turn it on, the screen brightness is ajustable with “Fn key” at night is OK but at day the brightnes is to low. How i fix it???

  5. 54
    Matt Says:

    I have replaced the lcd and the inverter on a gateway mx8738. I am going to try the multimeter test later this evening to see if the inverter is getting power. My screen now will only show a faint image. I dont have a lid closed switch, but was wondering if this computer has a magnetic switch and if so how would I test it or find it? I have also changed the lcd cable out but still nothing. When I boot the computer without an inverter connected at all it does the same thing as if it was connected and bad, dim screen. Any other things I should check before parting out this laptop?

  6. 53
    Eduardo Says:

    Hi!, i got a problem like that
    I have an Acer X193w and it turn normally but in 2 seconds the light turn Off and i can see the image, its kindda screensaver..
    can you help me?

    PS: sorry about the bad english bro
    Thanks!

  7. 52
    cj2600 Says:

    mauricio,

    sometimes the backlight turns on the sometimes not

    Can you see a very very dim image on the screen when the backlight is off? It’s possible you have a faulty inverter board.

    sometimes which binds and because the place connected to external VGA external monitor, but when I disconnect the external monitor it’ll turn brown

    I do not understand this part of the description. The external monitor turns brown?

  8. 51
    cj2600 Says:

    AL POE,

    here’s my story on a Dell 1501 the lcd screen won’t apprear until a couple of hand slaps on the left rear of the screen and will then only stay on with slight pressure supplied by my hand on the left bottom corner pulling towards me. This works in any postion of the screen and once the pressure is release it slowly fades to white and other colors.

    I’m discassing LCD failures in this post. I think your failure is similar to the example 7.
    I would say you have a faulty LCD screen and it has to be replaced. Apparently there is a bad solder joint somewhere on the LCD controller board and when you apply some pressure on the screen you temporarily fix it.

  9. 50
    AL POE Says:

    Great reading I’ll tell you,,here’s my story on a Dell 1501 the lcd screen won’t apprear until a couple of hand slaps on the left rear of the screen and will then only stay on with slight pressure supplied by my hand on the left bottom corner pulling towards me. This works in any postion of the screen and once the pressure is release it slowly fades to white and other colors. What is on the left side that would do this,,a bad ground or connector. I going fix this some way,,,Please help me.

  10. 49
    mauricio Says:

    dear,
    mauricio’m writing here from Brazil, I think its very good this site for people who are having problems in their notebooks, congratulations and grateful, I have a similar problem with a dell, sometimes the backlight turns on the sometimes not, sometimes which binds and because the place connected to external VGA external monitor, but when I disconnect the external monitor it’ll turn brown,

    I hope your answer.
    Thank you for teaching my teacher.

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