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.
If you find this article useful, please consider making a donation to the author. Thank you!
August 18th, 2011 at 2:22 pm
I HAVE A SAME PROBLEM WITH MY SAMSUNG N120 NETBOOK.WHERE CAN I FIND BACK LIGHT INVERETR,
?ANY HELP WIL BE HIGHLY APPRICIETED
July 26th, 2011 at 10:11 pm
would there be anything i can do to fix that?
July 13th, 2011 at 11:48 am
@ davidm,
It’s very likely. Sounds like there is a problem with the video cable connector on the motherboard.
July 11th, 2011 at 1:16 am
Hello, I need your help. I have a 2009 macbook white unibody, and the screen isnt working. the external monitor works perfectly, and ive taken the screen off and verified that it also works perfectly. I have even tried to order a new lcd cable and tried that but no luck, still nothing. at first i could see the desktop but very very dim, like the backlight wasnt working, but more recently when i try it, its completely black. am i correct in assuming it is a problem with the motherboard socket? if that is the case, can i do anything to fix it myself? anything at all? its out of warranty and im a college student, so taking it in for repairs is really out of the question for me. any help on this will truly be appreciated, and i thank you ahead of time for your response.
June 17th, 2011 at 8:30 am
dear sir,
I have an amilopro 2o1o,with backlight problem.i tried several invertor cards,I also connected the lcd backlight to one of the usb ccfl lights and the backlights lit up but with low brightness.when i switch the lid sw on and off seccessviley,the screens lights up.i made a continuity test for the cable from the mother board to the screen and was all good.i measured the outgoing voltages from the mother board and compared them with another laptop of the same brand and found the following,
pin 1 = 20 v ok
pin 2 = 20 v ok
pin 3 = 1.7 to 5 volt ok
pin 4 = 2.7 volt + 10 hz oscillation ok
the only difference i found was on pin3 where there is 160 hz of oscillation that should go down when 5v go to 1.7.
i wonder if you have a clue for this.
thank you.
June 4th, 2011 at 12:08 am
my laptop inverter was damage, I changed it, it is ok, but there are one side only of my lcd light, I changed Lcd with new one , the same problem found?
what can I do?
May 2nd, 2011 at 8:30 pm
Bekki,
I think your problem could be related to one of the following:
1. Possible bad connection between the video cable and motherboard. If that’s the case, reconnecting the cable might cure the problem. In Dell laptops the video cable connector usually located under the keyboard.
2. Could be bad video cable. In this case you’ll have to replace the cable.
3. Possible bad LCD screen. You’ll have to replace the screen.
Unfortunately, I cannot tell what is causing the problem without testing the laptop with another good known working screen.
May 2nd, 2011 at 11:00 am
Hello,
I am hoping you can help me, as I have final exams coming up and my laptop just went nuts. Yesterday, when I opened the laptop (it was powered on, just closed), the screen looked fine for a second but then started jumping around, horizontal and vertical lines started scrolling, and you could still see the desktop image behind all the scrolling but not so well. I restarted the computer and all was fine for a bit. I closed it and left it until today. It had powered off, and when I turned it on, there was absolutely no picture. The screen was black, but lit up (meaning there was a visible difference between screen being powered off and being powered on, but the screen was still black). I performed several hard power offs, removed battery, restarted, and the same. Finally, I connected to my desktop monitor, where the image came through fine, with all my programs and documents. While I was working from the desktop monitor, the laptop screen started going crazy again (although the desktop monitor was the actual functioning monitor). This time, it was white lines, and you could barely discern the desktop image. There was nothing I could do to make it stop. I tried applying pressure in various locations (mentioned on another message board) but no luck. Finally, it stopped, by itself. During this whole time, I was able to use the desktop monitor with no problems.
I am hoping you can tell me what the problem is/what to do to fix it. My warranty with Dell expired last December, and I have exams in less than a week. All my study documents are on the laptop, and using the desktop monitor seems to slow the speed of my laptop considerably.
Thanks,
Bekki
April 25th, 2011 at 8:07 am
Enabled,
It’s hard to tell what is causing the problem.
Could be bad connection between the video cable and motherboard. You can try reconnecting the cable.
Does it work fine with an external monitor connected to the VGA port? Can you get image on the external monitor?
Also, if your laptop has lid close button, try tapping on the button a few times. It’s possible the button got stuck in the closed position and the laptop “thinks” the display is closed.
April 22nd, 2011 at 9:13 am
Hi!
I have a little problem with a Acer Travellmate 8200 … the backlight is not working … I tried to change the display ( I thought that is the problem)that costs a bit more than I can afford and I had to ask my mom for giving me the money and it wasn’t just that … when I replaced the display … nothing happened … I thought that is the invertor , and I bought a new one … ( I think that works good despite that the display is still dark )
I tried to put a led to the invertor with “+” and “-” as in the other post picture and it works …
I have no ideea what can I do next … please help me as soon as possible …
Thanks a lot ,and I’m sorry for my bad english
Daniel,
RO