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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April 24th, 2010 at 1:44 pm
Omarey,
I think you should check connection between the cable and LCD screen/motherboard. Try reconnecting the cable on both ends.
It’s possible you accidentally disconnected the cable from the LCD screen (or motherboard) while replacing the inverter board.
Check connection between the cable and LCD screen first, it’s on the back side of the screen.
April 24th, 2010 at 1:22 pm
Erick Clavijo,
Yep, sounds like the inverter board failure.
Will it happen again if you replace the inverter? I don’t know.
Try replacing the inverter board.
April 18th, 2010 at 2:00 pm
I have a Dell Latitude X1 with the described problem. Screen comes on. Eventually goes very dim but screen is still visible. Works fine with external monitor. When I removed the bezel I saw that the inverter board had a burned out circular mark on the board itself and you could smell it. Seems like the inverter board could be my culprit but I’m wondering if the same thing will happen to the replacement inverter? Do I have a bigger problem?
April 12th, 2010 at 4:27 pm
I have a Toshiba Satellite M55-S135. I found information that led me to believe I was having a problem with my backlight inverter. On startup the picture would flicker for a few seconds then go out. I ordered a backlight inverter for my laptop and it did not illuminate the screen. The old one did but continued to go out. I got another one and installed it. The backlight now seems to illuminate the screen but no images come up. I can here the computer starting up and the sound of the windows screen sounds but nothing shows up on screen. Now when I tried reinstalling the old inverter it does the same thing as the new one. Any suggestions?
April 12th, 2010 at 3:34 am
Hi, I have a slightly different problem in my Dell laptop. my screen back-light is working properly when running on a battery. but when i attach mains with that, lights turns off but i can still see display in a bright light area. so i need to charge laptop and detach power adapter before using it, that is very annoying. please help me.
April 9th, 2010 at 12:04 am
Hi,
i was looking for a advise because i made a mistake by fixing a cable between the inverter and the motherboard. I changed two of the four small cables. After i started up i stopped the laptop as soon as i can. But i think the damaged was already done. My question is, is only the inverter broken or is there a wider communication between the inverter and the motherboard so that a part of my motherboard is broken. Is starts whithout the inverter but not startup sound. Lights are up and a spinning cooler and harddrive. Further no dark movement on the screen.
Thank you for reading.
greetings from Holland.
March 27th, 2010 at 5:07 pm
I replaced my Toshiba Satellite L305’s broken screen with a friend’s Toshiba screen. His inverter wasn’t working so I used mine (well, the same type as mine, my original inverter broke so I ordered one online). The screen back light would stop working randomly or anytime there’s a drastic resolution change, like when I hook it up to my television and unhook it or closing the lid then reopening it. I would open the lid and the screen would flash on for a second then the back light would turn off again. Also when ever the brightness goes down to a certain level, the inverter a loud noise. Is the problem the compatibility with the screen and the inverter?
March 14th, 2010 at 9:53 am
hello,
I am having a toshiba satellite laptop. The invertor was getting too hot below the screen. One fine day the screen went black but still can read under a tube light. I ordered a new screen invertor and replaced the old one. It works and still gets hot. Now after a week the screen again went black again.What could be the reason for the invertor getting hot.
Please help.
Regards
Anil
March 12th, 2010 at 1:53 pm
I would like to know what I can do because the computer that I bought is having a failure, in LCD screen.
When I start the computer the screen begins to sweep from the bottom to the top, this happens for about 3 minutes, and after that time (about) it gets still and looks normal, although on the bottom of the screen a single line of pixels continuous flickering and changing of color (rose, purple, blue).
Sometimes also after a while or when starting a new program the failure starts again.
I updated the Nvdia drivers, tried to change the screen resolution, but nothing changed.
I tested the computer with an external LCD and the problem disapeared.
I need to find a solution because it seems to get worse.
Yours sincerely.
*Product Type : Notebook
*Product Model : X83Vm
*Place of Purchase : USA
*Date of Purchase : 2009/1/1
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?