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.
If you find this article useful, please consider making a donation to the author. Thank you!
January 10th, 2011 at 9:14 am
I just found the screen by searching for Inspiron 6000 screen on Ebay, then made sure it matched up in terms of size, resolution, and WXGA. And of course the listing said it was compatible with my model. Is there anything else that has to be the same?
I will try reseating the cables…it was very difficult to get the video cable inserted at first. I realized after a few minutes that while the actual connection was the same, the new screen was not set up for a connector that had the little locking hinges on the sides, and once I took those off it slid in fairly easily.
Anyway again thanks for the help; if I don’t get a picture after reconnecting the cables I guess I’ll try to get an exchange.
January 8th, 2011 at 9:10 pm
Mike,
Apparently, the new screen is Glossy and the old one was Matte. If both screens are identical, it shouldn’t make a difference.
I cannot tell if your new screen is compatible. How did you find the screen?
By the way, didn’t you check connection between the LCD cable and new screen. It’s possible the cable not seated correctly and because of that you have no image. Try reseating the cable.
January 8th, 2011 at 7:12 pm
Thanks for the info man.
The screens are the same in that they’re the same size, resolution, and they’re both WXGA. They are different in that the new one is the more “shiny” screen that you usually see today, whereas the original was the more dull type that was around more often when I bought the laptop (approximately 5 years ago). Would that make a difference or is it more likely that the new screen is simply defective?
Thanks again for the help.
Mike
January 8th, 2011 at 6:58 pm
Mike,
This part sounds like the LCD screen failure.
Most likely it’s either not compatible OR defective LCD screen. Make sure you are using the right screen.
No, it’s not the inverter. You get backlight on the new screen, so the inverter board works properly.
January 8th, 2011 at 6:46 pm
Hello,
Just wondering if anyone could point me in the right direction w/ a problem I’m having. The bottom 3rd of my LCD stopped working completely (wasn’t getting any light etc), so I just purchased and installed a replacement. Upon power up I can see that the backlight is working (the screen is lit up), but the entire screen remains black throughout startup and never changes. I know the computer is working because I can hear the sounds from Window’s starting up etc. Is this a problem with the inverter then? Any information would be greatly appreciated; thanks!
Mike
January 8th, 2011 at 5:18 pm
boadi,
Can you use the laptop with an external monitor?
Does the laptop screen have backlight? Please provide more information.
January 7th, 2011 at 2:23 am
i have a laptop that i am working on it now it has a dark screen and u can not even see any thing on the screen how can i know that is the screen or the inverter or trouble-shoot LCD creen
December 29th, 2010 at 2:21 pm
Iguanodon,
I doubt you can test inverters without original laptops.
December 29th, 2010 at 6:10 am
Hi! I need to check several inverters that are in refection’s depot. I don´t have the laptops from where this inverters come from. Is there some way to prove if they works? Maybe connecting the a nominal voltage to certain terminal and how to identify those specific terminals of input voltage. Please, lend me and idea. Thank you.
December 20th, 2010 at 2:11 am
Hello,
Hope someone can put me on the right trackt.
I’ve got a extensa 5230 with total black screen (no dim picture too).
Things I have try so far:
Replaced inverter(2x) no results.
Replaced backlight bulb without results.
Then I connected a cracked old screen and see dim picture.
So where to start from here..
Hope someone can help me.
Thanks in advange
for more info please contact me mark0251 at hotmail dot com