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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December 27th, 2011 at 10:59 am
@ Al,
Could be bad connection between the video cable and motherboard. When you are applying pressure on the keyboard, you actually applying pressure on the video cable connector. This is my guess. I would try reconnecting the video cable first.
December 27th, 2011 at 6:50 am
Good morning,
HP Paviilion with dark screen. Works fine on external monitor.
Pressing firmly on keyboard will light the screen perfectly, but it goes off when pressure is released.
Thank you.
December 8th, 2011 at 6:43 pm
@ Marcus,
I assume that desktop monitors are similar to laptop monitors but this is just a guess. I don’t fix PC monitors and never done it before.
December 8th, 2011 at 7:27 am
Hi,I have a Dell St2010 Monitor for desktop,I had almost the same problem in Ur articular.Few weeks ago my monitor started flickering and 2 days ago while I was using,I heard buzzing sound coming out from my monitor,so I turn it off and turn it back on and my screen went dimmer,darker than it used to be(its like 90% of the power cut off)But in Ur article you stated that u experience reddish tone but I didn’t have that problem.I m just curious know is it my back light failure? I cant afford to buy a new monitor it cost a bomb
,thanks for sharing ur experience and great article,and sorry for my bad english,I hope you can reply as soon as possible 
thank you
November 2nd, 2011 at 8:51 am
@ Rox,
First, of all make sure the video cable is plugged correctly. Try reseating connection on the back of the screen.
If it doesn’t work, it’s possible you got a defective screen.
November 2nd, 2011 at 7:12 am
Can you advise me please? Toshiba Equium, screen replaced as it got damaged. After I replaced it and switched laptop on I only have about 5/6ths of my display. Settings etc for the widescreen are correct but I have a black section on the right. If I open a webpage I can actually hide part of it behind the black section! My taskbar is also stretched at the bottom. I basically have a square display on a widescreen panel and can’t change it. Any ideas?
October 6th, 2011 at 9:59 am
I bought a hp dv 2000 4years back.it was working fine till a month ago it started having similar problems. The screen goes blank suddenly and emits a continuous buzzing sound. This doesn’t respond to anything not even the power button. I need to shut the AC power and pull out the battery to make it stop. When i restart again it works fine for sometime and then it happens all over again. Any ideas on why this is happening nd what i do about it. Plzzz….help.
September 26th, 2011 at 11:53 am
Nahid?
Do you know where the closed lid switch is for the Acer Aspire 6930?
My new lcd screen is black but when connected to an external monitor, it is fine. When I shine a flashlight, the images show.
So, I am not sure it’s the new screen, the backlight, or the inverter.
Any help would be appreciated.
September 20th, 2011 at 1:18 pm
@ Nihad,
It’s hard to tell.
Your laptop should have a lid close switch button somewhere close to the left hinge. Try tapping on the button while the laptop is turned on. It’s possible the lid close got stuck inside the case.
Usually when you have a very dim image on the screen, it’s one of the following:
1. bad inverter.
2. bad backlight lamp.
3. stuck lid close switch.
4. bad connectin between video cable and motherboard.
5. bad video cable.
6. motherboard problem.
September 20th, 2011 at 12:08 pm
@ Manan Shah,
I assume there is no problem with image on the external monitor, right?
Move the laptop display. Does it make those lines to go away or make image even worse?
I think this could be one of the following:
1. Bad connection between the video cable and motherboard.
2. Faulty video cable.
3. Bad LCD screen (more likely).