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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March 11th, 2010 at 12:16 pm
In regarding to the two connector type you have shown in the picture. Are they inter-changeable? I mean if my original inverter has “big” connector plug into it, and, my newly purchased LCD screen happen has “small” connector at end of wire. Can I simply cut and connect the old one to replace the one on new screen?
March 2nd, 2010 at 11:00 pm
Tim,
Just search on Google for YPNL-N021A and you’ll find it.
I would recommend replacing it with the same inverter.
March 2nd, 2010 at 10:55 pm
Hi, I have a Dell Inspiron 1300, recently the inverter broke. But I can’t find this exact inverter. Si I would like to ask if I can use the inverter with P/N: YPNL-N021A IV12139/T-LF to replace the original inverter with P/N: PWB-IV11145/T/W2-LF?
Thank you very much for your kind attention and help!
.tim
February 21st, 2010 at 7:07 pm
cj2600,
Thank you for your reply. Here is the second part of my story. I got the new CCFL for replacement. I connected it to inverter and found it working when the original one did not. Bingo! Being sure that the lamp was the problem I replaced it with the new one on my DELL Inspiron 6000. When I assembled everything back and turned the notebook on I saw the familiar dull image. Whaaat!!! The first thing in my ming was that I damaged the back light during the installation. I disassembled everything back and suddenly it started working again. I tried to find the problem and bended slightly the screen and rechecked all the connection. Sometimes during those tests the lamp did not glow but i could not find the problem. I put everything back and now the laptop is working normally but already I had one situation when I had to restart the computer because of the dull image. I have no idea what to blame. It could be a electrical board on the screen, it could be the screen cable. I do not know what to do to be sure. I do not want to buy the new screen thinking that it might be cable. Could anybody give me piece of advise please?
Thanks!
February 11th, 2010 at 12:00 am
nicholas,
Most likely this is inverter related problem.
1. Try replacing the inverter board first.
2. If no help, most likely it’s bad backlight lamp inside the LCD screen. You’ll have to replace the screen (or backlight lamp inside the screen).
February 10th, 2010 at 11:57 pm
dsolod,
I guess you can buy a new CCFL lamp (it’s expenisve) and the laptop without installing the lamp into the LCD screen.
By the way, it’s not easy to replace the backlight lamp at all. I would suggest replacing the entire LCD screen if the backlight lamp is the problem.
February 10th, 2010 at 11:37 pm
Gerry,
Maybe you purchased a defective inverter? Did you buy it from a reputable seller?
I would try replacing it again just in case. It worked for 9 hours, didn’t it?
February 7th, 2010 at 8:43 pm
I have a Dell XPS Inspiron Laptop…I have similar problem on my screen like some of the others here. The screen went black 6 months ago but, sometimes booth normally and then a few seconds later…the screen with go black again. I can see very faint image. Through research and reading your advice…it sounds like a bad inverter. I replaced the inverter and it works for 9 hours straight…the next day when I boot the laptop…it’s black again. I can use the laptop using an external monitor…so I know my video card is good. Any ideas/suggestion? Please help. This site is very informative…Thank you so much in advance.
February 6th, 2010 at 8:34 am
Hello,
I am having similar problem but with a little detail. I get the very dull image on the screen only when my laptop (DELL Inspiron 6000) is cold. After running under this condition about 20 minutes and several restarts it begins showing the normal bright picture with NO problems after. Initially I thought that it might be either inverter or back light. Yesterday I replaced the inverter with no results. I am ready to replace the CCFL but now I am thinking that the problem could be something else.
If it’s a backlight problem then why it is working right now without any failures even when I restart laptop (because it’s warm). If it’s a connection, wire or soldering problem then it should failure from time to time during the work when i bend the screen and even touch the wires.
Does anybody have similar experience? Please give me a piece of advise! I would really appreciate this because I do not want to go through the CCFL replacing procedure if I am not sure that this is the case.
Thank you!
February 6th, 2010 at 6:44 am
Hello, I was wondering how one can pinpoint the faulty component, when the laptop had a flickering screen which now blacks out after a few minutes of use (but is visible under strong light). Is it the inverter issue, or perhaps the cables that feed it?
any ideas are appreciated. thanks