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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September 2nd, 2010 at 11:47 am
i have a acer aspire 8935g ,the screen is totally black but if you hold a flash light close to the screen every thing works normally i have been told as this is a new laptopit has no inverter and it is also a led screen 18″4 do i need a new screen help thanks
August 22nd, 2010 at 5:02 pm
Update: Meant to say it is still legible but is very noticable and distracting. When I run on battery power, it is worse and may be darker on both sides but more so on the left, the middle of the screen is not affected.
I connected the laptop to an external monitor and the display is FINE on the external. Thanks for any help you can provide.
August 22nd, 2010 at 4:26 pm
Hi,
I have been reading your site with great interest, but haven’t seen my exact problem. I have a Dell Inspiron 1720 laptop and last night I noticed that about 3 to 4 inches on the left side of the screen is darker than on the right side. It is still legible VERY noticible and is something I don’t feel I can live with. I spoke with Dell and was told I needed a new LCD, but I suspect after reading your articles, that maybe I need a new inverter and/or back light. I updated the Nvidia drivers which was no help. Suggestions? Thanks so much! Debby
August 15th, 2010 at 9:41 am
drew,
Did you test your laptop with external monitor? I assume external video works fine, right?
Try reconnecting the cable again. Maybe connecting between the cable and LCD screen is bad.
I think it’s either bad cable or LCD screen failure. Unfortunately, I cannot tell which one is causing the problem without testing your laptop with another known good screen.
August 13th, 2010 at 3:53 am
I have a Dell D830. It seems like th backlight is functional as if i use the blue fn key and adjust the brightness i can see teh screen adjust. However the screen is still blank.
I have changed the display cable, this cured the problem for about an hour, coincidence maybe?
Its the WUXGA screen so i’m not sure what the next port of call is? Any advice?
April 27th, 2010 at 1:45 pm
Bill,
I saw the same question in a different thread.
Again, test your laptop external video. If external video also shows green instead of black, most likely this is the video card failure.
If external video works fine and the problem appears only on the laptop screen, this is either bad LCD screen or video cable failure. Also, could be connection related problem. Before replacing any parts, try reconnecting the video cable connectors on both ends (back of the LCD screen and motherboard).