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.
Also, you can read the following posts:
Troubleshooting laptops with backlight failure.
Laptop screen shows strange colors. What could be wrong?
How to troubleshoot and fix laptop video problems.
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July 2nd, 2011 at 3:50 am
Dear sir
i have compaq v6000 laptop thir is i am problem faceing with display there is dim display on scree iwas repaced invertor but problem not solved, so kind help for this
May 30th, 2011 at 11:09 am
@ klikblogmu,
What kind of advice you are asking for? If you know the inverter is bad, replace it.
May 25th, 2011 at 7:11 pm
Very good article … I have a Toshiba laptop, inverter had twice replaced damaged …
ask for advice.
March 23rd, 2011 at 5:04 pm
Hey,
So I have a similar story to what a bunch of people have posted here. My screen is extremely dark (basically can’t see a thing) but for some reason my VGA to my external is working so that’s what I’m currently working off of. When I start the laptop up, I can see everything, even up until I log in. While the computer is loading all my programs, or maybe a bit longer, after a few minutes, the screen goes completely dark. If I put it to standby or hibernate and reactivate, the screen will reappear but will turn off in 3-10 minutes. Also, before this problem, I had opened my laptop off to clean out the fan with a compressed gas duster. After I put my laptop back together, this problem started to happen. Let me know what you think.
Cheers
March 6th, 2011 at 11:54 pm
I’ve browsed web page but no posting instructions. Compaq C700 laptop screen boots up white. Works fine on external monitor. I’ve testing an known working Toshiba LCD using instructions from this website (Swapped out Inverter & Cables)and Toshiba LCD boots up white screen also. This would lead me to believe LCD is not problem. Is it the Inverter? If it displays fine on external monitor does that mean on-board video is working fine on motherboard? Any help is appreciated.
March 5th, 2011 at 6:23 am
Hi, A friend of mine has a laptop where the LCD has almost a “black shadow” that expands and diminishes from the left side of the screen. Sometimes the LCD will work fine for hours, but usually one side of the screen is unevenly dark. Do you think this points more towards the bulb or the inverter? Thanks!
February 27th, 2011 at 11:30 pm
maxV,
Most likely it’s either bad inverter or faulty backlight lamp inside the screen.
If you replaced the inverter board and it didn’t fix the problem, most likely this is backlight lamp problem. In this case you’ll have to replace the screen.
You can try replacing the backlight but it’s not easy. I explained this process here: http://www.laptoprepair101.com.....ccfl-lamp/
No, it doesn’t mean that. If the lamp turns on for a second and then goes off, it could be a faulty lamp.
February 27th, 2011 at 2:55 pm
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.
January 15th, 2011 at 9:31 pm
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
January 15th, 2011 at 1:36 am
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?