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.
Check out my previous post about troubleshooting laptops with backlight failure.
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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
February 2nd, 2010 at 3:42 am
Sir,
I have a Dell Laptop inspiron 630m which i am facing a problem.the system works for a long time but suddenly LCD gets off blank. that time my cd drive works it comes out.and there is power light still working. then i need to switch it off by pressing the power button. Please solve me this problem.
Nixon
January 19th, 2010 at 5:38 pm
Hello, me again…OK put the old screen back in works perfectly, with the exception of the black area where the screen is broken. So I am gonna take a stab and figure the problem is the new laptop screen! Brilliant right? Didn’t think of it till I wrote the previous post…duh! So I am calling the screen vendor.
Thanks for all you do!!
January 19th, 2010 at 5:17 pm
Hello, I have an Acer Aspire 5516. The screen was broken when we received the laptop, but we did not realize that was the problem until it was returned to the Acer repair center and the tech called to tell us it was not a covered item. I have since replaced the lcd screen following your excellent directions. When I turned on the Laptop, it came on great, screen looked good. Yea….maybe 10 seconds, the screen dims out. Now I did some testing and it is NOT as dark as if the backlight is out.
The screen is now the correct brightness, however if I move the mouse, it dims. I do not know how long it takes for the screen to brighten up, as I have not seen it brighten, I just look and it is OK…This occurs on battery or outlet.
Any ideas???
I am going to take the backlight out of the old cracked lcd screen, how do I go about that?
Thanks again
January 18th, 2010 at 11:10 pm
There’s a diagnostic test at startup on my laptop that tells you if the inverter and backlight are working fine. My backlight is out completely doesn’t come on at all but under a bright light i can see mostly it’s just faint. I come across the test by accident i went to start in safe mode but clicked f12 instead and got a choice to do a diagnostics test so did it and it tested everything on the laptop including an heading for the LCD and the tests for it were inverter it passed, backlight passed and graphics passed. In fact nothig failed at all it took about an hour to check everything. The light went out without warning never did it before just went out and hasn’t come back on!
January 18th, 2010 at 3:38 pm
My Toshiba P205_S6287 was knocked off a table. It is still working however the 9″ plastic hinge attaching the top (lid) and bottom (base)broke on one side. The wires that go through that part are being pinched as small area of solid pixels appear on the display until I move the lid to a different position. I can’t determine which parts I’d need to fix the problem assuming it’s repairable. I’m concerned about further damaging the display wires opening and closing the lid.
Parts suppliers are also unsure as one said I needed a LCD cover assembly but another thought I needed a base assembly.
Your photos are most helpful and explanations clear but I’m stumped on this one.
January 17th, 2010 at 8:44 pm
hey thanks for a great tutorial but i was wondering where can i buy one of these back light testers?