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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September 17th, 2009 at 5:45 pm
I have a similar problem with my Desktop LCD, a LCD Flatron W2242T.
The bottom half of my screen is dark and has light spots right at the bottom, whereas the top half works perfectly. I was considering buying a new screen which wud set me back $300 = =”
but this site has given me hope, maybe i have a faulty backlight at the bottom. Any advice on what i should do?
thanks guys
September 7th, 2009 at 3:22 am
Hi, I have a problem with a laptop, Dell D830 when I turn it on, the screen brightness is ajustable with “Fn key” at night is OK but at day the brightnes is to low. How i fix it???
September 2nd, 2009 at 12:39 pm
I have replaced the lcd and the inverter on a gateway mx8738. I am going to try the multimeter test later this evening to see if the inverter is getting power. My screen now will only show a faint image. I dont have a lid closed switch, but was wondering if this computer has a magnetic switch and if so how would I test it or find it? I have also changed the lcd cable out but still nothing. When I boot the computer without an inverter connected at all it does the same thing as if it was connected and bad, dim screen. Any other things I should check before parting out this laptop?
September 1st, 2009 at 4:24 pm
Hi!, i got a problem like that
I have an Acer X193w and it turn normally but in 2 seconds the light turn Off and i can see the image, its kindda screensaver..
can you help me?
PS: sorry about the bad english bro
Thanks!
August 26th, 2009 at 9:31 pm
mauricio,
Can you see a very very dim image on the screen when the backlight is off? It’s possible you have a faulty inverter board.
I do not understand this part of the description. The external monitor turns brown?
August 26th, 2009 at 9:25 pm
AL POE,
I’m discassing LCD failures in this post. I think your failure is similar to the example 7.
I would say you have a faulty LCD screen and it has to be replaced. Apparently there is a bad solder joint somewhere on the LCD controller board and when you apply some pressure on the screen you temporarily fix it.
August 26th, 2009 at 11:41 am
Great reading I’ll tell you,,here’s my story on a Dell 1501 the lcd screen won’t apprear until a couple of hand slaps on the left rear of the screen and will then only stay on with slight pressure supplied by my hand on the left bottom corner pulling towards me. This works in any postion of the screen and once the pressure is release it slowly fades to white and other colors. What is on the left side that would do this,,a bad ground or connector. I going fix this some way,,,Please help me.
August 25th, 2009 at 8:16 pm
dear,
mauricio’m writing here from Brazil, I think its very good this site for people who are having problems in their notebooks, congratulations and grateful, I have a similar problem with a dell, sometimes the backlight turns on the sometimes not, sometimes which binds and because the place connected to external VGA external monitor, but when I disconnect the external monitor it’ll turn brown,
I hope your answer.
Thank you for teaching my teacher.
August 22nd, 2009 at 11:43 pm
Great test, saves lot of trouble and time and takes the guess work out of it.
August 20th, 2009 at 2:51 pm
Fantastic instructions – very clearly written with nice photos. It’s been really helpful to me. Keep up the good work.