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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November 16th, 2011 at 12:15 am
Hello, I have a acer laptop. My laptop screen can not stop at any point b’coz of its loose its connection with hardwere so how can i replace it and tell me b’coz of which part this fault arise?
Tushar
November 13th, 2011 at 9:18 pm
@ Shaun,
It’s hard to tell what is causing the problem without testing the laptop with another known good inverter board or backlight lamp.
This could be either bad inverter or faulty backlight.
Most likely the laptop works fine with battery because you have lower brightness settings for the battery mode and inverter/backlight can handle this mode.
November 13th, 2011 at 5:59 pm
I have a issue that I’m just lost on. All of a sudden, my screen went dark. I could still faintly see the image, so I know the system was still booting up.
Where I’m lost is the fact that when running on battery, the screen is perfectly fine. When it’s plugged in, it’s dark. Does this mean the inverter is going bad or is there another issue with my laptop?
Any help would be greatly appreciated here guys.
November 4th, 2011 at 10:01 am
@ c0dehunter,
When you test your laptop with new inverter and CCFL lamp, make sure the video cable still plugged into the LCD screen. On some laptop models the backlight will light up ONLY when you have video cable plugged into the screen. I guess it needs some kind of feedback from the screen. I don’t know if this is required for your laptop but do it just in case.
If the backlight still doesn’t work even with new inverter and CCFL lamp, most likely you are correct. It’s either bad cable or something wrong with the motherboard.
I guess just test both pins. I don’t think you’ll burn anything this way.
November 4th, 2011 at 9:43 am
Well, you see, that’s the funny thing. I already bought a new one and THIS ONE is the new one
I also bought a new CCFL and connected it to inverter but It doesn’t lit up. So I was guessing it must be something with cable coming from motherboard, right? That’s why I wanted to test Inverter to see if it gets electricity.
November 4th, 2011 at 7:20 am
@ c0dehunter,
Sorry, cannot tell. It’s a Dell inverter, right? A new (used) Dell inverter shouldn’t be very expensive on eBay.
November 4th, 2011 at 7:06 am
I want to test my Inverter but I dont know where is PIN 1 although I can see F1 printed. Is it that copper circle next to F1 sign?
I have provided a picture:
http://i.imgur.com/FSA13.jpg
October 26th, 2011 at 7:06 am
@ manish kumar,
How about video on the external monitor? Did you test external video?
Take a look at this post about white screen problems: http://www.laptoprepair101.com.....ned-white/
October 25th, 2011 at 3:41 am
i have a dell laptop model inspiron 1545.
I am getting a problem that my lcd screen will totally white after pressing power button. Can u tell me what problem is going with my laptop or any test by which i know the problem . u can mail me
October 6th, 2011 at 12:43 am
Hi
I have a Sony vgc-la1, I turn it on and the screen comes on fine for 2 seconds then goes off
Like it’s been turned off. So I press the standby button, to put it into stanby then press it again and it comes on for 2 sec then black screen again
Any ideas?
Thanks
Jon