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 28th, 2009 at 7:27 am
Hi,
Nice site to stumble upon.
I have a Laptop here with a strange problem.
its a Toshiba Equium m50-164 and the screen brightness seems to be backwards.
the Fn key for brightness works backwards so up is for lower and down is for higher.
now the problem that creates is that the screen brightness will not go up full (as the button is meant for darker and wont darken enough to fully turn off the inverter)
any ideas??
July 28th, 2009 at 3:09 am
Dell model no:pp01s lobtop power on and off when tested power 18.5v shows be in components all matherboard.doide 330j12 has no power.
July 25th, 2009 at 3:30 pm
This is great info. I’m a PC tech who does a lot of work for a lot of clients (sometimes I think too many).
I often left the LCD repair up to guess-work (whether it was the inverter or the LCD itself). For the most part I guessed (or deduced it correctly), but those ones I guessed wrong on were costly and time consuming mistakes I know I could have avoided.
I used to work with a group of technicians who would hoard their knowledge and never share what they knew with other techs. Needless to say nothing got done very well in that shop, I’ve since struck out on my own and have been doing very well.
Your little blog was very well written, informative and extremely helpful. I thank you for sharing your knowledge.
July 25th, 2009 at 10:18 am
I have a Dell Inspiron 1720 with Vista. If I just turn it on, I get a message to press any key to boot from floppy. It will only boot upcorrectly when I press the F8 key as soon as the DELL logo appears. When I ran diagnostics it gave error code 0322 and said the error was in accessing the LCD inverter. As long as I boot from the F8 key my LCD screen is fine, sharp and clear. It does not fit the description of a bad lcd inverter. Does anyone have any suggestions?
July 22nd, 2009 at 6:11 am
My son dropped his Gateway notebook. The LCD cracked. I removed it and order a replacement screen (actually 2). I installed both, but neither screen worked. I connected to an external monitor and everything worked.
Could I have received two bad replacement screens? or should I assume the inverter or backlight need to be replaced??
Thanks for any and all advice.
John
July 21st, 2009 at 6:02 pm
Hello
I have a PCG-K33 vaio that i need to repair, the problem is that when i turn on the laptop i can see the logo of vaio and even if I enter to the bios setup I can see everything as normal, but in the momemnt that windows starts the back light goes off. I tried to reinstall windows but same issue goes off int he middle of the installation. And the video card is working because if i connect the laptop to a monitor I can see everything and If i get closer to the screen i can see the images but really realy dark.
What can i do? do you think that is the Inverter or the Lamp Light?
Thanks for your help
July 21st, 2009 at 7:47 am
Shawn Smith,
Do a search for that on google. I fixed my gateway 7510gx with the same problem with just a hot melt glue gun. worked like a charm. There is a tutorial on the web on how to do it.
Matt
July 16th, 2009 at 7:59 am
Hi, I have a Gateway 7510GX the screen back lite flickers, dims and often goes out, you can still see whats on the screen when it goes out. I was thinking that it was the inverter bord. I dont have a good board to test it with. What do you think?
Thank you for your time, Shawn Smith
July 10th, 2009 at 5:03 pm
hello CJ,
I have a Toshiba m45 laptop. The screen has a native resolution of 1280 X 800. When the laptop is powered on, it only displays a 1024 X 768 resolution. This also happens in setup screen also. The image occupies the top left of the screen with the rest being black. I’ve tried connecting a known working lcd screen with same results. When an external monitor is hooked up it functions with a 1280 X 1024 resolution which is the native resolution of the external monitor. Therefor i presume that the on-board video works. Could this be a bad cable or bad on-board video?
Any suggestions would be greatly appreciated.
thank you!
JakeTT
July 3rd, 2009 at 1:10 am
sir i have a dead laptop i want to use its lcd on my pc how can its posebale