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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December 5th, 2009 at 3:42 pm
I’ve been having an LCD issue with my laptop as well CJ. Its a Toshiba Satellite M105-S3041. When I flip the LCD screen open it’ll be on from 1 degree all the way up to 15 degree, but after that it’ll turn off. I ended up opening to check the connectors, etc and everything seemed fine. I’ve created a video to show you the issue. The screen works perfectly between 1 – 15 degrees. The monitor output works perfect as well.
http://www.youtube.com/watch?v=9c8cvbiiBmY
December 5th, 2009 at 4:37 am
My daughters laptop hp pavilion dv6000 entertainment displays wavey colours/ smudge difficult to discribe but when i plug my desktop monitor in a get a great picture.
Iv bought a new screen and it looks just the same. Iv uninstallled and reinstalled display adaptors and all still looks the same.
Any thoughts please please please ??? Daz
December 2nd, 2009 at 3:02 pm
Dell inspiron 1000 screen blacks out when (even slightly) adjusting position of screen towards close or open. The HD LED and power LED stay lit. No HD spin or fan. 3-finger salute does nothing. Can only do hard shut down and power up to revive. I have no problem if I just touch or squeeze the display; only problem when pivoting on hinges or when shaking the desk enough to adjust the display’s position. If it’s open at 90 degrees, for example, and I then open it to 91 degrees or close it to 89 degrees, display and fan shut off. As if sleeping. I exposed the hinges and made sure the sleep switch is not being triggered. Could it be a short in the cable running from the system board to the display? if so, where to get it and how to replace?
I’d appreciate any thoughts before I send it to Dell hell (recycling center)?
Thanks
December 1st, 2009 at 2:33 am
I think I messed up my last post by trying to add your response to my original post. So here it goes again. I have taken out the CCFL light from the display panel, reassembled the laptop and tested the light. The CCFL lit up but started emitting a metallic sound and after a while went off. I tried it later again (the laptop is working with an external monitor and I left the front bezel out to have access to the inverter at will) and found that the CCFL did not light up nor was there any sound. Could you tell me what I should replace? The video cable has been unplugged from the system board and re-seated without any difference in the display; it remains blank. BTW, the first time I booted up the computer with the CCFL outside, a very dim screen appeared but not on subsequent boots. Please advise.
November 30th, 2009 at 12:34 pm
Looks like the video card is working properly, I agree with that.
1. Bad inverter board? I don’t think so. When inverter goes bad, you still should see a very fain image on the screen. From your description is sounds like you have no image at all, so it’s not related to the inverter board.
2. Bad backlight lamp? I don’t think so. There is no image on laptop screen at all, so it’s not related to the backlight either.
I think it’s either bad LCD screen (most likely) or faulty video cable (less likely).
Before you replace anything, try reconnecting the video cable connector on the motherboard. It’s located under the keyboard cover, close to the right hinge. Maybe the video cable is not making good connection with the motherboard.
Thanks for your well-thought opinion. Last weekend I dismantled the LCD screen, thanks to your and another website’s step-by-step guide and took out the CCFL bulb. I re-assembled the laptop and left the bezel cover out so as to be able to reach the inverter at will. After making sure that the computer is otherwise functioning normally and I did not mess it up in the process, I connected the CCFL bulb. It lit up immediately, but started making a metallic repeating sound like a key emits when it gets accidentally pressed and remains depressed for a while. After a while the light went off. I kept the computer that way (front bezel removed) and tried the CCFl again just now. It did not light up. Incidentally, I noticed a very dim display on the screen while booting up the first time after removing the CCFL. I am not sure whether subsequent boots were also displaying the dimmed screen or the screen was entirely black. Please advise what you think from this development. Thanks.
November 29th, 2009 at 11:51 pm
Steve Midwinter,
If the screen is BLACK and BLANK, the problem is not related to the inverter or backlight lamp.
With failed inverter or backlight you still should see a very faint image on the screen.
I would definitely test the laptop with an external monitor.
If external video works fine but nothing appears on the screen, it’s possible you have a failed video cable OR the cable got disconnected from the motherboard.
1. Try reconnecting the cable.
2. Replace the cable.
If both, the internal and external screens do not work, it’s possible that you have a faulty memory module.
Again, test the laptop with the external monitor before jumping to any conclusion.
November 29th, 2009 at 11:16 pm
Lay V,
I don’t think this is problem with the inverter board. A faulty inverter board cannot cause lines on the screen.
I think you have a faulty LCD screen (most likely) or there is a problem with the video cable (less likely).
Just in case, try reconnecting the video cable on both ends, on the motherboard and back of the LCD screen. Make sure both connectors are plugged correctly and secure.
If reconnecting the cable doesn’t help, I guess you’ll have to replace the screen again.
November 29th, 2009 at 10:40 pm
Henry,
Go to the device manager and uninstall display adapters. Restart the laptop and let it redetect the adapter (and LCD screen). Doing that might fix the problem.
Take a look at this post: http://www.asklaptopfreak.com/.....placement/
The author had exactly the same problem after replacing the LCD screen on his Dell laptop.
I agree. From my experience (and I replaced hundreds of them), the inverter either work or not. I really doubt that your problem is related to the inverter board.
November 29th, 2009 at 2:24 pm
Subrata,
Looks like the video card is working properly, I agree with that.
1. Bad inverter board? I don’t think so. When inverter goes bad, you still should see a very fain image on the screen. From your description is sounds like you have no image at all, so it’s not related to the inverter board.
2. Bad backlight lamp? I don’t think so. There is no image on laptop screen at all, so it’s not related to the backlight either.
I think it’s either bad LCD screen (most likely) or faulty video cable (less likely).
Before you replace anything, try reconnecting the video cable connector on the motherboard. It’s located under the keyboard cover, close to the right hinge. Maybe the video cable is not making good connection with the motherboard.
You can buy a brand new LCD screen on eBay for less than $80 and replace it yourself. Take a look here: HP Pavilion DV6275US LCD screen.
Here are instructions for replacing the LCD screen in HP Pavilion dv6000 series notebooks.
November 28th, 2009 at 5:20 am
My three-year-old HP Pavilion DV6275US (RP284UA) shows distorted colors (not pinkish hue) on the Windows screen while booting up, keeps on flickering till the desktop comes up and soon after, with a series of horizontal black bands that go from bottom to top, widening all the time, goes blank. No image is visible after that, even with a flashlight. Moving the dislay panel back and forth does not make any difference. I hooked it to an external monitor and ran for hours without a hitch. That seems to exonerate the video card (NVidia GeForce Go 7400, integrated to the mobo). Looks like there could be three culprits 1) the inverter 2) the CCFL lamp 3) the LCD cable (an outside chance) or a combination of two or all of them! A local repair company of repute suggested replacement of the LCD screen that would set me back by Euro 195. I have read your articles with great interest and I think I can handle replacement of the the parts. Unfortunately, I have no way to test the unit with known good spares. Could you diagnose what is wrong and what I should order as replacement? Any help, comment, suggestions, posted on this page, would be appreciated.