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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June 27th, 2009 at 10:38 pm
Brian,
Can you boot to the desktop or it fails before the laptop finish loading Windows?
Enter the BIOS setup menu and wait. Does it fail in BIOS?
June 27th, 2009 at 10:17 pm
moteldanny,
There is no way you can tell without testing the laptop with a known good inverter board. If you spilled milk on the keyboard (not display), probably your failure is related to the motherboard.
June 26th, 2009 at 8:43 pm
i just split the soymilk on my laptop, while i didn’t get a chance to shut it off, and right now, when i open my laptop, the screen is very dark, but i can still see a little,very very dark, do you think it is inverter problem or it is motherboard’s….
June 24th, 2009 at 4:48 pm
What if the screen comes on for a while then goes out. It does the same with an external monitor
June 23rd, 2009 at 9:18 am
I have an issue with my laptop that I think is connected to the screen inverter. all the white colors (only true white, off white is fine) turns into this pink color with white lines and all the black (True black) turns into this green flashing color. if I move the screen about it some times gets better or worse but sadly my screen case is broken so I have to prop it up against pillows. Is this simply an issue with my screen inverter or with the wires, and is it fixable or not? can you recommend a good repair shop is Boise, ID that won’t tell me to get a new laptop? thank you for your time.
June 18th, 2009 at 3:53 pm
I had computer in rain. Screen is still quit legable with some distortion of images. I ruled out motherboard and video card. So I thought it was the screen. I ordered new one hooked up the inverter to backlight backwards. Some sizzle then went dark. I then installed connector properly and screen lit up fine, but image is still garbled. Did I ruin new screen or ids the problem lcd cable. Thank You.
Dave
June 12th, 2009 at 8:55 am
Hi CJ,
Thank you so much for your thorough review! It is very helpful!
My Inspiron 1520 has recently had random backlight failures in
which the screen goes dim. It always re-lights if I sleep and resume (or whenever I start an external monitor). The backlight stays on for a few minutes and then fails again.
Does this sound like a failing inverter or could there be other explanations?
Thanks again!
Cameron
June 11th, 2009 at 4:03 am
sounds just like my laptop turn it on goes for about 1 or 2minute then goes black. computer is still working in want program it is in . when i turn it on the screen has a pink tinge to it.
June 10th, 2009 at 11:28 am
Hello i have a fujitsu siemens with geforce 6800 and my screen show many pink spots and when i twist the computer it get better, but on external monitor the image is always very good.
Do you have an ideia of what could it be? Many thanks
June 9th, 2009 at 6:43 am
“”Yes you can but I believe you’ll get positive readings only if both the back light lamp and inverter are in a good working condition. The magnetic field will be created only if the inverter is loaded, right? But what if one of the parts is faulty and there is no magnetic field around the inverter? How can you tell if it’s a bad inverter or back light lamp?”"
An inverter takes a (relatively) high amperage low voltage signal and turns it into an extremly high (KV range) low amperage (mA range) signal. There are 4 failure points; CCFL, Inverter, Cable, and Mobo. Couple of things to keep in mind:
A: If the CCFL fails it will not load the inverter, so no mag field.
B: If the Cable fails (pretty much it can only fail one way), no voltage = no mag field.
C: If the inverter fails, you may or may not get voltage; if the CCFL is loading the inverter and the inverter is not producing enough voltage you’d probably not get a mag field.
D: If the mobo fails, no voltage or not enough.
Say the unit is DOA and you *THINK* it has a backlight issue, the ampmeter is the 3-second solution to see if you’ve got a functioning inverter. Most laptops go through a power-post procedure similar to a desktop psu and will load the inverter if it passes even if the unit fails to post.
I like the idea of ordering a $15 CCFL and using that to test; I hadn’t thought of that before and come to think of it to test this properly you’d need an assortment of CCFL’s and cable converters. It’d be easy to build a professional soluton from epoxy, wood, 2×3′s, plexiglass, some screws and a label maker.
I do keep a spare 12” LCD on hand, as well as a 20” chassis with an inverter hooked into it. You can load a high-end inverter with a low-end LCD ccfl. The problem with either is if you use a 12” LCD CCFL to test a 16” inverter anbd the 16” inverter is ok producing voltage for as 12” ccfl but not a 16” ccfl you wouldn’t know it until you plugged it into the 16” ccfl.