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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July 12th, 2010 at 9:52 pm
I Have a preasrio v2000 I am having problems with the screen being solid white on the outer edges and in the middle a hazey white with white dots. I replaced the mother board thinking it was that. It still does this. any suggestions?
July 2nd, 2010 at 10:23 am
i have a Lenovo Y510 laptop with me.
i work fine but from we days my laptop flip is not stand in 90 degree position it totally get flat 180when i open my laptop . i have give support from backsight to keep it in 90 degre position
June 11th, 2010 at 12:46 am
Boy oh boy what a nightmare it can be figuring it out. My dell inspiron laptops screen went dark and I could not figure it out. Thank G-D for this article, at least I knew that the only way to know for sure is to get either a backlight or inverter so I figured I will go with an inverter first , found mine, installed it and viola, it turned out being the inverter. Now shes working like a charm. Thanks guys
June 4th, 2010 at 7:38 pm
Hi! I just replaced a bad ccfl in my laptop. It went well. Next problem- when I turn it on with the lcd unplugged the whole screen lights up white but when i plug the lcd in and turn it on everything stays black. Is this a common symptom of a bad inverter? I don’t know if this helps but when I opened up the lcd the old ccfl was in two pieces and all black where the pieces met. The area over the inverter was getting really really hot. That makes me think that the inverter got too hot and broke the light. Any ideas on where the problem might lie?
May 21st, 2010 at 5:42 pm
Hi, I had ordered a new 15.4 inch screen for my Toshiba A 105. I noticed that the wired from the backlight of the new screen is of the “BIG” type … whereas the inverter itself accepts only the “SMALL” type. Do you have any suggestions on how I can replace the wires from the backlight? Thanks.
April 27th, 2010 at 1:48 pm
Young,
The ThinkPad screen might require a different video cable.
April 27th, 2010 at 1:17 pm
Tester,
Did you mean the inverter board? You were wrong, a green hue on the screen cannot be caused by the inverter failure. Only the LCD screen backlight could be affected by the inverter failure.
Did you replace just the LCD screen or you replaced LCD and video cable?
If you replaced the LCD screen and video cable, then you are correct. Most likely this is the motherboard failure.
April 27th, 2010 at 11:39 am
I have a toshiba A135. Everything works except that the LCD is mostly a green hue. I replaced the converter and still same prob. Then I purchased a broken A135 for parts and replaced the entire LCD screen and it is still doing the same thing. Output from the VGA connector is fine.. I have to assume the problem is with something on the motherboard ?
April 26th, 2010 at 12:25 am
Hi, great posting.
I have a toshiba laptop w/ ati radion 3100 card installed.
its lcd is 15.4″ wxga and manufactured by LG.
I have a spare wsxga+ 15.4″ lcd screen pulled from a thinkpad t61, and is manufactured by samsung. I tried to install samsung lcd to my toshiba, but the screen would not light up. I switched back to the LG and it works fine. what would be the problem? does the samsung lcd needs different inverter? or vga cable needs to be replaced. I checked the video cable and it fits. Please help.
thanks,
April 24th, 2010 at 1:46 pm
Sharma,
I’ve seen some people complaining about the same problem before but I don’t know the solution.
Enter the BIOS setup menu and find the LCD screen brightness settings. Reduce the screen brights for AC mode and test your laptop with AC adapter again. Does it help?