In this post I explain how I test the LCD screen inverter board in a laptop computer.
The screen inverter failure is very similar to the backlight lamp failure. In both cases the screen gets very dark and the image on the screen becomes very faint, barely visible under a bright light.
If you suspect the inverter board failure, I know only one reliable way to test that. It’s either replacing the inverter board with a known good one and see if it works, or connecting a known good backlight lamp and see if your presumably bad inverter lights it up.
In most cases I go with the second method – testing the laptop with a known good backlight lamp. Why? Because backlight lamps are pretty much universal. The same backlight lamp will work with many different inverters as long as they have matching connectors. I’ll talk about these connectors later.
The inverter board is located inside the display panel under the LCD screen. In most laptops you can access the inverter board if you remove the LCD screen bezel. The inverter board has connectors on both ends. The left side of the inverter is connected to the LCD cable. The right side of the inverter is connected to the backlight lamp which is mounted inside the LCD screen. Check out this display diagram.
To make sure that inverter board is getting power from the motherboard (via the LCD cable), you can test it with a multimeter. In my case I connected the “+” lead of the multimeter to the pin 1 on the connector and the “-” lead to the ground trace around the screw hole. I got about 19.4V DC on that side of the inverter, so it’s getting power from the motherboard.
WARNING! If you accidentally short something on the inverter while testing it, you can damage the inverter or even the motherboard. Proceed on your own risk! Not sure? Don’t do that!
So, the inverter is getting power from the motherboard, but the screen is still dark. Apparently, it’s either bad inverter or failed backlight. Let’s test it with a known good backlight.
Here’s what I’m going to do:
1. I will unplug the LCD screen from the right side of the inverter. Basically, I’m unplugging the LCD backligth lamp which is located inside the screen.
2. I will plug in my known good backlight lamp which you can see on the picture below. Please notice that my test backlight lamp is shorter than the screen, but for the test purpose that’s OK.
Results I’m expecting:
1. If my test backlight lights up, the backlight lamp inside the screen is bad and there is nothing wrong with the inverter board. If that’s the case, you’ll have to replace the LCD screen or replace the backligth lamp (which is not easy at all).
2. If my known good backlight lamp stays dark after I turn on the laptop, most likely we have a faulty inverter board. If that’s the case, you’ll have to replace the inverter board and it’s relatively easy.
There are two different types of backlight connectors, you can see them on the picture below. The top one (big) is not as common as the bottom one (small). I do most of my test with a backligth lamp which has a small connector.
IMPORTANT! If you decide to buy a new backlight lamp for test, you have to make sure that the connector on the lamp matches the connector on the inverter. Very often backligth lamps are sold without any wires attached. If you plan to use this backlight as a test equipment, you’ll have to find one with wires as I have on the picture 3.
You can buy a cheap backlight lamp with wires here.
Finally, when you ready to test the laptop, unplug the LCD screen from the right side of the inverter.
Plug in your test backlight lamp and turn on the laptop.
In my case, the backlight lamp lights up, so the inverter board works properly.
Check out my previous post about troubleshooting laptops with backlight failure.
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July 1st, 2009 at 4:44 am
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.
June 30th, 2009 at 1:54 pm
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?
June 29th, 2009 at 8:55 am
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.
June 29th, 2009 at 8:54 am
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.
June 27th, 2009 at 11:36 pm
Nathan P,
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.
June 27th, 2009 at 10:38 pm
Brian,
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?
June 27th, 2009 at 10:17 pm
moteldanny,
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.
June 26th, 2009 at 8:43 pm
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….
June 24th, 2009 at 4:48 pm
What if the screen comes on for a while then goes out. It does the same with an external monitor
June 23rd, 2009 at 9:18 am
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.