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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April 1st, 2013 at 5:44 pm
@ Dražen Šarić ,Croatia
If you can hear Windows sound probably the motherboard works properly.
Take a closer look at the screen. Are you sure there is no video on the screen? Maybe the image is very dim?
If you can see a dim image, it’s either bad inverter board or failed backlight lamp inside the LCD screen. Try replacing the inverter board first.
NOTE: some laptops will not display on external monitors on startup. In order to test video on the external monitor properly it’s necessary to unplug the video cable from the motherboard. Can you do that? Can you get image on the external screen when the video cable unplugged from the motherboard?
March 28th, 2013 at 1:40 am
Regards !
Please can you help me …. I have problem with my lenovo 3000 N200 ,when i turn on laptop after while i can hear windows sound ,but can’t see anything on laptop lcd neither on external monitor .Is it graphical card on motherboard …
Thanks in advance …
February 26th, 2013 at 11:20 am
Why I power my laptop Hp pavilion dv5,It brings purple colour,wat could be the problem.Thax
September 27th, 2012 at 5:02 am
i have one laptop before 2 days one problem created in it, now it is complately on but its display light come (not brightness) , i attech it with other crt or lcd monitor it is working properly
September 11th, 2012 at 8:44 am
how come my hp laptop compaq nx9010 has a black screen computer comes on and runs but notthing but black out screen. please help.
September 3rd, 2012 at 12:48 am
hi i just read the problems with baklights nad inverters, when i look at my laptop(dell latitude d630) i noticed that were the inveter is its lose how come i dont know? and theres bit of dirt in it.what could be the problem,lights,inverter or dirt coursing all of this.please help
thanks for helping us
May 31st, 2012 at 11:22 pm
Hi
My w700 was used more than 3 years. last week, inverter was not working. I checked it by multimeter: power input was ok but no power output. Video cable and backlight were working well. I purchased a new inverter from IBM parts center, installed and then problem solved.
But after a few days, the problem came back, checked by multimeter, the new one was broken again. I checked the inverter board, and found ohm of a pair of small capacitors was zero (very quickly to zero and meter never changes). It seems the capacitors were damaged. The two boards have same capacitor problem. This pair of samll capacitors are located just on top of the coil. Video cable and backlight have no problem.
I don’t know if it is the capacitors making the inverter malfunction? something must be wrong making the board broken again, and why? Please can you help me to solve this problem. Thanks.
p.s. In most time this w700 uses external monitor only, and sometimes uses both screens.
May 21st, 2012 at 4:28 am
Can u pls explain how to check laptop inverter out put ( Ac voltage ) with the help of multimetre
April 24th, 2012 at 5:38 am
I have one MSI CR700 notebook from 2years and half. Last year I had to replace his display because it got broken.
This year it began doing the following: Sometimes, when working on darker environments(especially games, but also black background web pages) the image brightness become intermittent darker, and black at all after a while. Sometimes it becomes white at all, this sometimes even after powering on the notebook, also happened after I reinstalled windows at all, Before I installed the graphic card drivers which makes me think it should not be the video card.
Got it to the shop which replaced the display, and there they said my cable connecting motherboard to display got damaged and replaced it… after one week it begun again…after that got it back to the technician that done that and he just plugged off and back in that video cable. It worked fine for other 2 weeks, when it begun again. I also notice that it sometimes it reacts when I touch the screen (making problems disappear or making even worse) which makes me think there is somewhere, something making a bad connection to my display. What you think I should check? Is it possible that inverter or back light make the display both dark/black or white? And that not all the time…it may work fine for 3-4 days.
March 21st, 2012 at 3:21 am
Dell Inspiron 9300 with vertical lines on screen. Finally decided to get new screen which came with inverter but blank. Transferred inverter from old screen and can see full image on new screen but very faint. Inverters are not the same part no, even though both screens from same manufacturer. Does this point to faulty inverter supplied with new screen? I have refitted old screen with original inverter for time being and have good brightness with increasing number of thin vertical lines.