How to test screen inverter

posted in: Screen, Troubleshooting | 253

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.


253 Responses

  1. alex,

    Hardware passed tests. When i hold down the function key and cycle f6 the screen comes back on for a few seconds then turns back off. It is working with a monitor.

    Take a closer look at the screen after it turns off. Is it completely blank or you still can see a faint image.
    If the faint image is still on the screen, most likely it’s either failed inverter board or bad backlight lamp.

  2. @ Jean-Philippe,

    Everytime I power on my computer, the backlight works for few seconds. Then, the screen starts making a crazy noise and the light turns off.

    I can still see my desktop icons under a very big light.

    After all Ive red about the subhect, I still cant figure if its an inverter, backlight, lcd or video cable problem.

    I don’t think this is video cable related problem. Don’t order the video cable.
    Most likely it’s either bad inverter or failed backlight lamp.
    Hopefully your new inverter will fix the problem. If not, you can try replacing the backlight lamp or just replace the whole LCD screen.
    It’s possible to replace just the backlight lamp but it’s not easy. Take a look at this guide.
    http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp/
    If it looks difficult, replace the screen.

  3. Hardware passed tests. When i hold down the function key and cycle f6 the screen comes back on for a few seconds then turns back off. It is working with a monitor.

  4. Jean-Philippe

    I got this black scren problem.

    Everytime I power on my computer, the backlight works for few seconds. Then, the screen starts making a crazy noise and the light turns off.

    I can still see my desktop icons under a very big light.

    After all Ive red about the subhect, I still cant figure if its an inverter, backlight, lcd or video cable problem.

    I already ordered a new inverter on eBay, which I should receive shortly. But if it doesnt work, I wonder which new part I should get first (10$ video cable, 20$ backlight, 100$ lcd screen)…

    Thanks for answering

  5. tushar,

    I have a acer laptop. My laptop screen can not stop at any point b’coz of its loose its connection with hardwere so how can i replace it and tell me b’coz of which part this fault arise?

    Sounds like both display hinges are broken and has to be replaced.
    It’s necessary to disassemble the display panel and take a closer look at the hinges.

  6. Hello, I have a acer laptop. My laptop screen can not stop at any point b’coz of its loose its connection with hardwere so how can i replace it and tell me b’coz of which part this fault arise?
    Tushar

  7. @ Shaun,

    I have a issue that I’m just lost on. All of a sudden, my screen went dark. I could still faintly see the image, so I know the system was still booting up.

    Where I’m lost is the fact that when running on battery, the screen is perfectly fine. When it’s plugged in, it’s dark. Does this mean the inverter is going bad or is there another issue with my laptop?

    It’s hard to tell what is causing the problem without testing the laptop with another known good inverter board or backlight lamp.
    This could be either bad inverter or faulty backlight.
    Most likely the laptop works fine with battery because you have lower brightness settings for the battery mode and inverter/backlight can handle this mode.

  8. I have a issue that I’m just lost on. All of a sudden, my screen went dark. I could still faintly see the image, so I know the system was still booting up.

    Where I’m lost is the fact that when running on battery, the screen is perfectly fine. When it’s plugged in, it’s dark. Does this mean the inverter is going bad or is there another issue with my laptop?

    Any help would be greatly appreciated here guys.

  9. @ c0dehunter,

    I already bought a new one and THIS ONE is the new one I also bought a new CCFL and connected it to inverter but It doesn’t lit up. So I was guessing it must be something with cable coming from motherboard, right?

    When you test your laptop with new inverter and CCFL lamp, make sure the video cable still plugged into the LCD screen. On some laptop models the backlight will light up ONLY when you have video cable plugged into the screen. I guess it needs some kind of feedback from the screen. I don’t know if this is required for your laptop but do it just in case.

    If the backlight still doesn’t work even with new inverter and CCFL lamp, most likely you are correct. It’s either bad cable or something wrong with the motherboard.

    That’s why I wanted to test Inverter to see if it gets electricity.

    I guess just test both pins. I don’t think you’ll burn anything this way. :)

  10. c0dehunter

    Well, you see, that’s the funny thing. I already bought a new one and THIS ONE is the new one :) I also bought a new CCFL and connected it to inverter but It doesn’t lit up. So I was guessing it must be something with cable coming from motherboard, right? That’s why I wanted to test Inverter to see if it gets electricity.

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