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!
October 22nd, 2007 at 9:34 am
Hey…
I have been having problems with backlight/inverter recently.
After reading up on many websites, i figured i had inverter problem since my lcd was dim to the point where i couldnt see anything. I ordered the inverter from ebay and got it today. After replacing it, i noticed that the laptop works fine for few (2) seconds and then goes dim again. If i tap on the lcd close button, it again turns on for (2) seconds and then goes back dim.
I am not sure what the problem is :S could it be that the backlight is bad or can there be something else?
thanks in advance
October 16th, 2007 at 8:44 pm
Angelos,
I would try replacing the inverter board first. There is a good chance to fix the problem and it’s way cheaper and easier then replacing the backlight bulb or the LCD screen.
October 15th, 2007 at 3:02 am
Yes, I can see a little. Especially if it is dark in the room I can see more. Also I am not hearing any noise from inside.
October 13th, 2007 at 7:50 pm
Angelos,
It can be inverter or backlight lamp. You cannot tell until you test the laptop with a known good inverter or a known good backlight lamp. You’ll have to guess.
You said the screen is black. How black it is? Can you see faint image on the screen?
October 11th, 2007 at 3:50 pm
Before I order the inverter I would like to have one more question that might help if it is the lamp or the inverted. In the begining, before the screen is totaly black(not exactly black but with this shadow), sometimes suddently the light turned on until I switch off the laptop but next time again black. This hapenned for 3-4 times and then all black…This indicates if it is inverter problem or backlight lamp? Thank you…
October 5th, 2007 at 12:15 pm
Morris Rosenthal,
I didn’t have chance to go through all troubleshooting charts but I think this is a REALLY GREAT idea.
October 4th, 2007 at 8:18 am
With the high pitched noise, especially if it’s coming from th elid, I’d suspect the inverter. You might check out the LCD troubleshooting flowchart I’m working on:
http://www.daileyint.com/hmdpc/lcd.htm
I actually popped into this thread to ask if the owner had any feedback on the flowcharts, but couldn’t figure out how to contact him.
Morris
September 27th, 2007 at 4:08 am
Shawna,
I think you might have two different problems with your laptop and it’s always hard to troubleshoot any laptop with two or more different issues.
This hight pitched noise and flickering screen could be caused by a faulty inverter board or failing backlight lamp. I would try replacing the inverter board first, you have a better chance to fix this issue. If it doesn’t help, you’ll have to replace the backlight (witch means replacing the LCD screen).
A few days ago I was troubleshooting a Dell Inspiron 600m with a similar problem. In my case the screen was making noise and it flickered as yours, but when the backlight was on, the white colors had reddish tone. I connected my test backlight lamp and it stopped flickering and the noise was gone. So in my case it was a faulty backlight lamp.
When your screen flickered, did you notice that white background had reddish tone? If it was normal white then most likely you have just a faulty inverter board. You’ll need more equipment (as spare backlight lamp or inverter board) to make troubleshooting more accurate.
I don’t like this one. So you had flickering screen/no backlight/faint image for a while and then it disappeared and now you have nothing? Could be a problem with the motherboard, video card, CPU or memory.
I think you should take your laptop to a professional repair shop for diagnostics as you have more then one problem.
September 27th, 2007 at 3:47 am
Mike,
First of all, check out this page about extended warranty for Satellite M30X, M35X, A70 and A75 laptops. Hurry, this extended warranty ends soon (I believe in November 2007). You might qualify for a free repair if you purchased your laptop in the U.S.A.
If you are asking about a short black wire attached to the video harness, then you don’t have to connect it to anything, just route it alone with the video harness.
So, you’ve replaced the LCD screen and the inverter board but still have no backlight? There might be a problem with the video cable. Also, it’s possible that you have something wrong with the motherboard but I doubt it because you have external video. I would try replacing the video cable next. Did you try reconnecting the video cable on the motherboard, just in case, to make sure it’s making a good contact with the motherboard?
It’s also possible but to find out you’ll have to disassemble the laptop and assemble “outside the laptop case”. Not sure if you want to go this route and I would do it only as a last resort.
September 25th, 2007 at 4:19 pm
Hello, I’ve been having to live without my laptop since December 31st of last year because of this problem. I don’t have the money to take it in and am trying to save up to fix it some way. I’m wondering if anyone can help me identify the problem because I’ve read and speculated a few different things.
Last year the LCD light began flickering and I could hear a faint high-pitched noise. If I closed the monitor and re-opened to “wake” it back up, the light would work for a few minutes and then go out again. It eventually went out completely. Now, I can barely (barely!) see the screen (and as of a few minutes ago, for some reason I cannot get a screen at all). I have a desktop at home also, and tried to hook the monitor up to the laptop to no avail. I went through troubleshooting and cannot figure out why the laptop will not comply with the external monitor. I read through your posting and am a bit confused (I’m not good with the hardware aspect, so I’m clueless right now) so I’m hoping you have some insight…
Laptop: Dell Inspiron 5100
External Monitor: MultiMedia Series M70 (ViewSonic M70 on RAGE 128 VR)
Anyone have any ideas? Inverter board? LCD? Something else?