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. cj2600

    Young,

    I have a spare wsxga+ 15.4″ lcd screen pulled from a thinkpad t61, and is manufactured by samsung. I tried to install samsung lcd to my toshiba, but the screen would not light up. I switched back to the LG and it works fine. what would be the problem?

    The ThinkPad screen might require a different video cable.

  2. cj2600

    Tester,

    I have a toshiba A135. Everything works except that the LCD is mostly a green hue. I replaced the converter and still same prob.

    Did you mean the inverter board? You were wrong, a green hue on the screen cannot be caused by the inverter failure. Only the LCD screen backlight could be affected by the inverter failure.

    Then I purchased a broken A135 for parts and replaced the entire LCD screen and it is still doing the same thing. Output from the VGA connector is fine..

    Did you replace just the LCD screen or you replaced LCD and video cable?

    I have to assume the problem is with something on the motherboard ?

    If you replaced the LCD screen and video cable, then you are correct. Most likely this is the motherboard failure.

  3. Tester

    I have a toshiba A135. Everything works except that the LCD is mostly a green hue. I replaced the converter and still same prob. Then I purchased a broken A135 for parts and replaced the entire LCD screen and it is still doing the same thing. Output from the VGA connector is fine.. I have to assume the problem is with something on the motherboard ?

  4. Hi, great posting.
    I have a toshiba laptop w/ ati radion 3100 card installed.
    its lcd is 15.4″ wxga and manufactured by LG.
    I have a spare wsxga+ 15.4″ lcd screen pulled from a thinkpad t61, and is manufactured by samsung. I tried to install samsung lcd to my toshiba, but the screen would not light up. I switched back to the LG and it works fine. what would be the problem? does the samsung lcd needs different inverter? or vga cable needs to be replaced. I checked the video cable and it fits. Please help.
    thanks,

  5. cj2600

    Sharma,

    I have a slightly different problem in my Dell laptop. my screen back-light is working properly when running on a battery. but when i attach mains with that, lights turns off but i can still see display in a bright light area. so i need to charge laptop and detach power adapter before using it, that is very annoying.

    I’ve seen some people complaining about the same problem before but I don’t know the solution.
    Enter the BIOS setup menu and find the LCD screen brightness settings. Reduce the screen brights for AC mode and test your laptop with AC adapter again. Does it help?

  6. cj2600

    Omarey,

    I have a Toshiba Satellite M55-S135. I found information that led me to believe I was having a problem with my backlight inverter. On startup the picture would flicker for a few seconds then go out. I ordered a backlight inverter for my laptop and it did not illuminate the screen. The old one did but continued to go out. I got another one and installed it. The backlight now seems to illuminate the screen but no images come up. I can here the computer starting up and the sound of the windows screen sounds but nothing shows up on screen. Now when I tried reinstalling the old inverter it does the same thing as the new one. Any suggestions?

    I think you should check connection between the cable and LCD screen/motherboard. Try reconnecting the cable on both ends.
    It’s possible you accidentally disconnected the cable from the LCD screen (or motherboard) while replacing the inverter board.
    Check connection between the cable and LCD screen first, it’s on the back side of the screen.

  7. cj2600

    Erick Clavijo,

    I have a Dell Latitude X1 with the described problem. Screen comes on. Eventually goes very dim but screen is still visible. Works fine with external monitor. When I removed the bezel I saw that the inverter board had a burned out circular mark on the board itself and you could smell it. Seems like the inverter board could be my culprit but I’m wondering if the same thing will happen to the replacement inverter?

    Yep, sounds like the inverter board failure.
    Will it happen again if you replace the inverter? I don’t know.
    Try replacing the inverter board.

  8. Erick Clavijo

    I have a Dell Latitude X1 with the described problem. Screen comes on. Eventually goes very dim but screen is still visible. Works fine with external monitor. When I removed the bezel I saw that the inverter board had a burned out circular mark on the board itself and you could smell it. Seems like the inverter board could be my culprit but I’m wondering if the same thing will happen to the replacement inverter? Do I have a bigger problem?

  9. Omarey

    I have a Toshiba Satellite M55-S135. I found information that led me to believe I was having a problem with my backlight inverter. On startup the picture would flicker for a few seconds then go out. I ordered a backlight inverter for my laptop and it did not illuminate the screen. The old one did but continued to go out. I got another one and installed it. The backlight now seems to illuminate the screen but no images come up. I can here the computer starting up and the sound of the windows screen sounds but nothing shows up on screen. Now when I tried reinstalling the old inverter it does the same thing as the new one. Any suggestions?

  10. Sharma

    Hi, I have a slightly different problem in my Dell laptop. my screen back-light is working properly when running on a battery. but when i attach mains with that, lights turns off but i can still see display in a bright light area. so i need to charge laptop and detach power adapter before using it, that is very annoying. please help me.

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