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 17th, 2008 at 12:14 am
I have a Satellite Pro A10 with dim screen, I have tested the backlight and that works fine, I bought another inverter but nothing changed although this could be faulty too. I would like to know can anyone tell me where the lid close switch on this laptop is please. So that I can check this problem before buying yet another inverter. Thankyou
September 15th, 2008 at 10:12 pm
ray,
Could be anything and there is no way I can tell you what is wrong without testing the laptop.
Try this. Turn on the laptop without the hard drive installed. Can you boot to the HP logo?
Try reconnecting the memory module. Move it to the empty slot.
I posted some suggestions for troubleshooting dead laptops in this post.
September 14th, 2008 at 12:20 pm
My Hewlit and Packard laptop screen stays completely blank and iits like its trying to keep starting up.No movement on the hard disk light on the front.Tried to get ti to go into safe mode by pressing F8 but nothing.Any ideas.Had this problem recently but then after doing the same thing of continualy waht sound like it was turning off and on the screen loading sign came on with the black background.This time nothing comes on at all!!!!!!
August 17th, 2008 at 6:30 pm
My laptop frequently have just a blue/gray screen when I
boot up. I’ve tried every thing I can, but it doesn’t work. Any suggestions?
August 16th, 2008 at 6:58 pm
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August 7th, 2008 at 7:56 pm
Unfortunately, replacing the inverter didn’t fix my problem. I’ve gotten a replacement backlight, but it doesn’t have connectors as it was advertised, so I have to solder it. Since the inverter I bought was refurbished, I wondered what are the odds I got a faulty one?
Since I now have 2 inverters and 2 backlights, I should be able to test different combinations, but I only have one set of wires so it’s more difficult…
July 30th, 2008 at 12:29 pm
Fernando,
It happened to me before. In some cases the problem looks like bad inverter/backlight lamp, but it’s bad motherboard.
That’s why I always test a faulty laptop with known good inverter and backlight lamp before I jump to a conclusion.
July 30th, 2008 at 10:44 am
I had the same issue with the backlinght very dim on the lcd screen on a dell laptop. So I replaced the inverter but it had the same issue, then I went ahead and replaced the entire lcd screen with inverter and backlight and still had the same issue, so I tried moving the motherboard to another laptop and still had the same issue so I just replaced the motherboard and that worked.
July 29th, 2008 at 10:26 pm
Joy,
That’s interesting! I’ve never heard about this test. I’ll try it on different laptops with inverter/backlight failures.
July 28th, 2008 at 7:13 pm
My Dell laptop went black today, after flickering just a bit for the last week or so. From everything I’ve read, I’m thinking it is the inverter since it works with external monitor and it actually lit up once when I brought it out of the screensaver mode. I talked to the Dell tech support and finally got the guy to tell me one of the tests to try. It sounds crazy, but he said if you turn it upside down and then power up, if the screen lights up you know it’s not the backlight, so it’s likely the inverter.
Well, I didn’t power down, but closed the lid so it went to standby. I turned it upside down and then opened it and voila! the screen looked normal. The one thing I still wonder about is something I read about a failing backlight causing the inverter to shut itself down. That scenario isn’t proven or disproven with my test. So I guess I’ll get a cheap inverter and see what happens.