How to test screen inverter

posted in: Screen, Troubleshooting | 251

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.


251 Responses

  1. Hi, I have a problem with my laptop screen.
    The screen is very dim, black but it is still possible to recognize something on it. If one press the “lid close” switch or the LCD/externalmonitor(fn+f8) the screen comes to normal for about 1 second and goes black again. If I connect it to an external monitor I can work on the computer, so the PC is fine and the problem is on the laptop screen.

    After reading in internet I was sure it could be the inverter so I bought a new inverter and replaced it.
    with the new inverter the problem persist and the PC behaves exactly the same. So I sopouse the problem is not in the inverter (or i bought a defect inverter¿?).
    I tried also turning on without inverter. In this case I have the same dim black screen but when I press the “lid close” switch or the lcd/externalmonitor key (fn+f8) the 1 second long “normal screen” flash does not appear.

    If I can see a normal screen even for 1 second ..Does it means the screen and the lamp are ok?
    I hope somebody can help me.
    thanks a lot.

  2. Mohammed

    Hello my laptop is very dim and i cannot brighten it. i do see it booting up properly but with low visibility. Can someone tell me what i need to replace the light bulb or the inverter

  3. my laptop screen works okey but at times displays horizontal lines and the display hangs.on a slight touch of the plastic holding the screen it works ok.what could be the problem?

  4. Memphis,

    On my screen image is shown as a negative, you can see the outlines of images

    The photo you provided is bad quality and hard to see what’s going on.
    But if the image turned negative, most likely this is LCD screen failure. You’ll have to replace the screen.

    I think the inverter is not a problem because the screen lights up

    That’s right. This is not inverter issue.

  5. Greetings!

    On my screen image is shown as a negative. I think the inverter is not a problem because the screen lights up! I think it is a flat cable, I’d love to hear your opinions!

    thanks

  6. I just found the screen by searching for Inspiron 6000 screen on Ebay, then made sure it matched up in terms of size, resolution, and WXGA. And of course the listing said it was compatible with my model. Is there anything else that has to be the same?

    I will try reseating the cables…it was very difficult to get the video cable inserted at first. I realized after a few minutes that while the actual connection was the same, the new screen was not set up for a connector that had the little locking hinges on the sides, and once I took those off it slid in fairly easily.

    Anyway again thanks for the help; if I don’t get a picture after reconnecting the cables I guess I’ll try to get an exchange.

  7. Mike,

    The screens are the same in that they’re the same size, resolution, and they’re both WXGA. They are different in that the new one is the more “shiny” screen that you usually see today, whereas the original was the more dull type that was around more often when I bought the laptop (approximately 5 years ago). Would that make a difference or is it more likely that the new screen is simply defective?

    Apparently, the new screen is Glossy and the old one was Matte. If both screens are identical, it shouldn’t make a difference.
    I cannot tell if your new screen is compatible. How did you find the screen?
    By the way, didn’t you check connection between the LCD cable and new screen. It’s possible the cable not seated correctly and because of that you have no image. Try reseating the cable.

  8. Thanks for the info man.

    The screens are the same in that they’re the same size, resolution, and they’re both WXGA. They are different in that the new one is the more “shiny” screen that you usually see today, whereas the original was the more dull type that was around more often when I bought the laptop (approximately 5 years ago). Would that make a difference or is it more likely that the new screen is simply defective?

    Thanks again for the help.

    Mike

  9. Mike,

    The bottom 3rd of my LCD stopped working completely (wasn’t getting any light etc)

    This part sounds like the LCD screen failure.

    so I just purchased and installed a replacement. Upon power up I can see that the backlight is working (the screen is lit up), but the entire screen remains black throughout startup and never changes.

    Most likely it’s either not compatible OR defective LCD screen. Make sure you are using the right screen.

    Is this a problem with the inverter then?

    No, it’s not the inverter. You get backlight on the new screen, so the inverter board works properly.

  10. Hello,

    Just wondering if anyone could point me in the right direction w/ a problem I’m having. The bottom 3rd of my LCD stopped working completely (wasn’t getting any light etc), so I just purchased and installed a replacement. Upon power up I can see that the backlight is working (the screen is lit up), but the entire screen remains black throughout startup and never changes. I know the computer is working because I can hear the sounds from Window’s starting up etc. Is this a problem with the inverter then? Any information would be greatly appreciated; thanks!

    Mike

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