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 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).
September 20th, 2011 at 10:20 am
Hi I need one help to identify what is problem in my laptop LCD and how can i solve.I have Dell inspirion 1520 model and i am getting 2 lines in LCD .Can Please Help me to know what is problem.
Here is the Screen Shot of my laptop http://postimage.org/image/2wvgyb23o/
Thanks in Advance.
September 20th, 2011 at 6:40 am
I received the LCD cable and it fixed the black screen problem with the HP dv9700 laptop.
The inverter was not required.
September 18th, 2011 at 10:50 pm
I have a Dell D610 and I do not have an image on the screen. I can see it with a flashlight, and it works with an external monitor. I have replaced the inverter and the backlight. I tested the backlight before I put it all back together and it worked fine. Once I put it back together, I wasn’t able to see the screen unless I used a flashlight. Any idea what the issue may be?
September 13th, 2011 at 10:37 am
Great article,
I am currently troubleshooting a backlight issue myself
My question to you is this, as a computer repair technician, ordering a proper backlight or inverter board usually means buying it online and waiting for the shipment to come in. Is there any way to get around this? Maybe a universal backlight/inverter board that you can use on virtually any laptop to test what the problem is first before ordering? Thanks! If you could email the reply that would be great!
September 8th, 2011 at 6:46 am
Thanks for the reply I cannot see anything i’m not sure if the screens material itself is very dark.
I actually wiggled the cable by the hinge and it came back on for a few seconds then I wiggled again and image went greenish colour.
now i cannot get it to work anymore.
I will try the cable and see what happens.
September 7th, 2011 at 11:07 am
@ Fabiog,
First, I would check connection between the video cable and motherboard. Maybe it’s just loose connection.
Are you sure the LCD screen has no image at all? Look very closely. If there is image at all, I would try replacing the video cable first.
September 7th, 2011 at 10:44 am
I have a dv9700 pavilion laptop and the screen is completely black ,I cannot even see any faint images.
External works fine ,I have tested the lamp with another computers inverter and it works fine.
Since I cannot test the cable nor inverter I am thinking of ordering the LCd cable ,inverter or both which one would be the best in this case?
Thanks