This laptop came for repair because of the LCD screen backlight failure. My customer complained that the laptop LCD screen is black but the laptop works with an external monitor.
Here are my steps for troubleshooting this laptop with the backlight failure.
First of all, I tested this laptop with an external monitor connected to the VGA port and the external monitor worked absolutely fine. I was able to get crystal clear image on the external screen even though the internal screen didn’t light up. If the external screen works fine, then most likely there is nothing wrong with the video card.
Notebook display assembly diagram
After that I took a closer look at the laptop LCD and noticed that the screen is not completely black. The laptop screen still works but the image is very very dull, you barely can see it. It means that the screen still gets data signal from the video card, but for some reason the backlight lamp doesn’t work.
From my experience I know that this problem can be related the lid close switch, faulty inverter board or bad backlight lamp. I checked them one by one.
If you have a similar problem, make sure the lid close witch moves freely. The lid switch is a small button located close to the LCD screen. This button triggers the hibernation or sleep mode when the screen is closed. If the lid close switch is dirty, it might get stuck inside the laptop case and cut off the power from the inverter board. The inverter board works as a power supply for the backlight lamp and if there is no power coming to the inverter board, the backlight lamp will not light up either.
In my case the lid button worked properly, it didn’t stuck inside the case. When I was pressing on the button very fast, I was able to light up the screen but only for a fraction of a second. The image wasn’t bright and it had a pinkish tone. A pinkish tone usually indicates a problem with the backlight lamp, not the inverter board.
Even though I suspected the backlight failure, I decided to test this laptop with a new inverter board just in case. But it didn’t help. The screen didn’t light up even after I replace the inverter board. So, I was right, this problem is not related to the inverter board.
Finally, I disconnected the screen backlight lamp connector from the inverter board and connected my test backlight lamp (I removed it from another cracked screen). For the test purpose, you can buy a new backlight lamp here. Try to find a backlight with the connector already attached to it, so you can plug it into the inverter board. Make sure the connector on the backlight lamp is similar to the connector on your LCD screen.
As soon as I turned on the laptop, my backlight lamp lighted up. Yep, that’s the problem. The laptop screen has a faulty backlight lamp.
Here’s another laptop with backlight failure
This laptop video fails in a little bit different way. In this case the backlight lamp hasn’t failed completely.
The laptop starts with video on the screen but the background has reddish tone, the screen flickers and it makes noticeable buzzing noise coming from the backlight and inverter area. After a few minutes the backlight turns off by itself and the buzzing noise stops. When the backlight is off, the image on the screen is still visible but it’s very dark.
I removed the screen bezel and connected my test backlight lamp.
My test backlight works absolutely fine. The lamp doesn’t flicker and there is no buzzing noise. So, this laptop needs a new backlight lamp.
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May 13th, 2009 at 12:26 pm
Jane,
I think it depends on the laptop model. Take a look at my last post: How to test LCD screen inverter in a laptop
I’m using the same inverter with the backlight lamp removed from a smaller screen and it works just fine.
May 13th, 2009 at 8:04 am
Is the inverter the same for a 15 or 17 inch lcd ?
May 8th, 2009 at 4:20 pm
I have a HP Pavilion. My girlfriend unplugged it while it was running, she thought the battery was in.
When I start it now the power on button is flashing continuously. ram, hdd, monitor are not dead I think because I basically tested them.
Does someone know what the flashing could mean…
pls notify me kactusrvm (at)hotmail (dot) com
April 27th, 2009 at 8:56 pm
Lee,
You are correct, on of these parts should have fixed it.
Did you try all possible part combination? For example, the old motherboard and old LCD with both new and old inverters, both motherboards with the old and new LCD/inverter, etc…
April 26th, 2009 at 6:00 am
I have a HP Pavilion with a backlight problem, I first replaced the inverter and that didn’t work. Then a new display and again that didn’t work. Next the video/display cable which still didn’t help. Then the motherboard with no help. There is no visible lid close switch. Seems like one of these parts should have fixed it. I have had a dim display through all of this that can be seen using a flashlight. Any other ideas other that a new computer?
April 4th, 2009 at 11:25 am
Thank you. Before I had been wondering why my notebook screen looks a bit reddish on the sides when it’s running on battery. Now I know why, thanks to your article.
February 18th, 2009 at 2:54 pm
I just bought a Gateway MT6451 with a broken lcd. Ordered a new one, installed it and nothing. So I put the old one back in and that works. So I decide to test the inverter and backlight, both work. I then unlug the broken display backlight but leave the video cable hooked to the bad display, hook the new display’s backlight to the inverter. power up… backlight works…so while the laptop is on I unplug the broken lcd video cable and plug it into the new one…it worked. But only till I reboot. I did it like 6 time and it worked that way each time. Oh and the vga and svideo ports work also. Anyone know why its not turning my new lcd on?
February 18th, 2009 at 1:37 pm
Hey cj2600 and thanks for the very, very usable information on your website. I have some questions though.
I have an Acer Aspire 3610, with backlight problems.
Just until now it hasn´t been given any light from the screen, so i figured i would check to see if the cables where inserted correctly. They seemed fine, but when i booted up the laptop again the screen lit up, amazingly.
I had it running for a few minutes without doing anything, and then suddenly it went dark again. There is no light but i can still see the picture from a specific angle.
I restarted it, and there was the light again, but it disappeared again and did this with the light disappearing in smaller intervals. Eventually the light was gone just after the BIOS sequence, and i stopped doing this when there were coming some strange noises and a not so nice smell from the laptop.
So now im afraid to do anything with the noise and the smells.
What do you think is wrong with my laptop?
I have tested the inverter with my multimeter, and it says around 42 KHz until the screen goes black and it goes down to 0 Hz.
Can it be the inverter which is causing the trouble?
Is the inverter supposed to give away frequenzies even when the CCFL is dead?
Is there only one standard in CCFL’s? Can everyone of them be soldered on to the power connectors, taking that i have the right size for my screen?
I think thats all for now, thanks in advance for the answers!
// Adam
February 15th, 2009 at 5:34 am
Thank you. This is so helpful. I am trying to troubleshoot my Toshiba Qosmio F-15. I have a unreadable screen that goes between red and green garbled lines and black screen with garbled white symbols. I can kind of see some icons when I boot in safe mode. Your guide is helping me. Hopefully I can figure it out. I am thinking it has something to do with the fact that I actually used it for 2 hours one day. Ha!
January 27th, 2009 at 6:35 pm
Thanks a lot all I had to do was clean thelid close switch and My backlight works fine, sweet