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 15th, 2009 at 7:22 am
My problem is a little different from others I’ve read. After turning on the unit and heating up for 10 minutes, I get a small semi-circular black spot that appears in the lower right hand corner of the screen. It appears as about the size of a thumb print. It will remain and after the unit runs for additional 10 minutes or so, the screen will start to “flicker” and become distorted. I have not just left it on to see if it will go totally black. After shutting off and cooling then restarting, the screen is clear until it warms up again. Would this be the inverter or a screen problem?
December 11th, 2009 at 10:31 am
Hi:
Thanks for the useful site. I have a laptop which half the screen is completely black (the bottom half). When I connect the laptop the external monitor, it is no problem to display to external display. SOmetimes when I open and close the lid, it works fine but after a while, the bottom half of the screen freezes (i can not move my mouse over it).. I opened the laptop and check all
the cables from the motherboard to the LCD screen and inverter. Does this sound like a bad LCD screen?
Thanks
Leo
December 5th, 2009 at 4:57 am
I have an Acer Aspire 5315-2153.
When I boot up the monitor works, then after a few minutes it fades to white, then grey. after about ten minutes, it comes back and works fine.
Ideas?
November 30th, 2009 at 12:21 pm
“I think it’s either bad inverter board (most likely) or failed backlight lamp (less likely).
It’s very unlikely that you have a faulty lid close switch. I’ve been fixing laptops for 5 years and seen very few failed lid close switches.
1. Try replacing the inverter board.
2. Try replacing the LCD screen (because it’s very hard to replace just the backlight lamp).”
I respectfully disagree here I’ve seen many laptops where the lid-switch either both mechanical & magnetic version has failed.
It’s much cheaper & easier to find this switch attempt to clean or just disconnect it before buying a inverter/back-light on a whim. The mechanical switches can usually be cleaned or just manipulated until then start functioning again. The magnetic sensors range in price depend what else is on the PCB. Many types like Sony Viao’s require replacement of the track-pad. That is unless your happy unplugging the switch and using a external mouse
November 29th, 2009 at 11:58 pm
lee,
I think it’s either bad inverter board (most likely) or failed backlight lamp (less likely).
It’s very unlikely that you have a faulty lid close switch. I’ve been fixing laptops for 5 years and seen very few failed lid close switches.
1. Try replacing the inverter board.
2. Try replacing the LCD screen (because it’s very hard to replace just the backlight lamp).
November 21st, 2009 at 5:06 am
hi there i think i have a Philips 15NB57 series. i think my problem lies within the backlights hinge sensor as the screen its self works fine and i get a display through an external monitor. the backlight switches on for a split second during startup and also will do when inserting or removing the connection for the external monitor it will also come on when the lid is in a near closed position but only briefly again. is there anyway i can bypass the hinge sensor through the settings or is it something i’ll have to get repaired? (am using vista if that helps)
November 13th, 2009 at 3:56 pm
Godfirst,
Try to switch video from external to internal mode using Fn+F8 keys.
Press and hold down the Fn key and at the same time press on F8 (try to press a few times if it doesn’t work).
November 11th, 2009 at 5:51 pm
Hi everyone
i dont know if this is a backlight problem.
I just opened the laptop(dell inspiron 5150) to dust the fan and after closing it began to function but refused to display. I tried several times making sure that the video cable is okay but it still did not come up.
It displayed very fine on an external monitor but never on the lcd.
I dont know if i must open plastic covering the lcd before i can find lid close switch because i cant find it on the surface.
I dont just want to go such great lenght because it was functioning before i got it loose.
Please help me, is it a backlight problem or something else?
I just did not expect it to grow a problem so fast
November 2nd, 2009 at 4:28 pm
Terry,
I really doubt that you can test the backlight lamp with an ohmmeter but I’m not sure 100%.
I don’t test them, I replace them.
November 1st, 2009 at 8:52 am
Thanks for posting all this great info.
Question about backlight testing – Should a good backlight have continuity across it’s terminals if it’s good? I was assuming yes, but all the backlights that I tested (1 out of 5 was good for sure) had no continuity when tested with an ohmmeter.