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. Han Ching

    my notebook is toshiba L300-P502 got one problem, i cant think about what happen. when i pluged-in ac adapter while the battery full charged. the screen brightness might gone up and down flickers itself. until i turn off the ac power, the problem gone. what is the problem?

    if i plug-in ac only sometime it may damn dark and bright dark and bright. the damn dark and bright dark and bright gone if i press Fn+F6 / F7, sometime i on for 4 hour without a problem. even the battery installed. damn notebook just 1 month old, my birthday gift after saving for 2 month to buy it.

  2. It’s got me beat and I hate that. Any ideas would be appreciated. Daughters laptop she says thinks her brother might have dropped it, no visible damage. Screen very dark. Changed power settings to never turn off screen when on mains. Then changed bios to default. Additional monitor works fine and is cloneing laptop screen. Gets 15v from motherboard so changed inverter. Next changed backlight. Both backlights have 16k ohms resistance which seems reasonable. Updated virus definitions and ran full scan. Can’t think of any logical reason why it doesn’t work? Can you help me be a good dad?

  3. also, it’s pretty worthy to note that the inverter itself gets very warm while in use. I checked its temperature and it was up to 102 Fahrenheit, I’m thinking that is abnormally high for inverters.

  4. I have a Fujitsu LifeBook C Series computer, and it is having intermittent problems, that I believe to be in the inverter. I’m looking for a opinion from more experienced folks. Every once in awhile (usually after having been off for a while), the screen will go out, literally. It will freeze the image on the screen and warp it while it goes out. Simply moving the screen on its hinges fixes the problem and puts the LCD right back where it should be – in perfect looking condition. It may take up to 3 or 4 hinge movements before it finally comes back. I’ve never not been able to bring it back. The inverter is located directly under the LCD.

  5. cj2600

    Nathan P,

    all the white colors (only true white, off white is fine) turns into this pink color with white lines and all the black (True black) turns into this green flashing color. if I move the screen about it some times gets better or worse but sadly my screen case is broken so I have to prop it up against pillows. Is this simply an issue with my screen inverter or with the wires, and is it fixable or not?

    Your problem is not connected to the inverter board. The screen is bright and you can see it, so the inverter works properly.
    I think it’s either bad video cable or LCD.
    You said, you can make it better or worse if you move the screen. I think your problem is connected to the video cable. I would try replacing the cable first.

  6. cj2600

    Brian,

    What if the screen comes on for a while then goes out. It does the same with an external monitor

    Can you boot to the desktop or it fails before the laptop finish loading Windows?
    Enter the BIOS setup menu and wait. Does it fail in BIOS?

  7. cj2600

    moteldanny,

    i just split the soymilk on my laptop, while i didn’t get a chance to shut it off, and right now, when i open my laptop, the screen is very dark, but i can still see a little,very very dark, do you think it is inverter problem or it is motherboard’s

    There is no way you can tell without testing the laptop with a known good inverter board. If you spilled milk on the keyboard (not display), probably your failure is related to the motherboard.

  8. moteldanny

    i just split the soymilk on my laptop, while i didn’t get a chance to shut it off, and right now, when i open my laptop, the screen is very dark, but i can still see a little,very very dark, do you think it is inverter problem or it is motherboard’s….

  9. What if the screen comes on for a while then goes out. It does the same with an external monitor

  10. Nathan P

    I have an issue with my laptop that I think is connected to the screen inverter. all the white colors (only true white, off white is fine) turns into this pink color with white lines and all the black (True black) turns into this green flashing color. if I move the screen about it some times gets better or worse but sadly my screen case is broken so I have to prop it up against pillows. Is this simply an issue with my screen inverter or with the wires, and is it fixable or not? can you recommend a good repair shop is Boise, ID that won’t tell me to get a new laptop? thank you for your time.

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