Troubleshooting laptop with backlight failure
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.
Entry Filed under: LCD Screen Repair
77 Responses to “Troubleshooting laptop with backlight failure”
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Pages: « 8 7 6 5 4 3 2 [1] Show All
September 24th, 2007 at 12:34 pm
I have a toshiba satellite M35X-S149 with what appears to be a bad LCD backlight. So i bought a “new” LCD screen to install. However, once I installed the screen, the same thing happened that the last screen was doing. The video would show up VERY faintly and the external video would work, but the backlight would not work. I tried switching inverter boards and nothing helped. I think I may have a grounding problem. I think i’m not putting the black wire with an “eye-hole” at the end in the right spot. Does anyone know where it goes? Please Help!
September 23rd, 2007 at 10:47 pm
Michael,
First, I don’t know the name and model of your laptop. Second, in most cases you cannot upgrade the motherboard.
September 23rd, 2007 at 9:56 pm
Eugene,
If you still can see the image on the laptop screen then the problem is not related to the inverter board or backlight lamp. When you have a dead inverter or backlight lamp, the whole LCD screen will be dark, not just some vertical lines.
From your description I would assume that you might have a faulty LCD screen. There is a possibility that your problem is related to the video cable.
September 23rd, 2007 at 1:31 pm
i’ve got a laptop diagnosed and they said i have a bad motherboard due to waterdamage. i want to take out the motherboard and put in a new one. however, rather than just put in the old outdated one, is there another motherboard you reccommend that would fit inside the laptop?? and how much would that run compared to putting an old but working replacement??
September 21st, 2007 at 7:17 am
Hi, I think my back light inverter may be faulty. I’ve checked it with an external monitor and it’s OK. You can see the image on the laptop but it looks like every other vertical LED is not lit? ie if you look at the letter “S” it would look like a “$” I have a Compaq N800vp, product DJ125T. The question is, can I get a replacement back light or will I have to buy a whole laptop screen?
Yours suggestions would be very much appreciated
September 11th, 2007 at 1:49 pm
Wojciech,
It could be just a loose connection on one of the inverter ends. Try reseating these connectors, it might help. Also check connection between the video cable and the motherboard/video card.
You cannot tell with part is failing the inverter board or the backlight lamp without testing the laptop with a known good backlight lamp (or inverter). I think you might have a dead backlight bulb because the laptop was dropped.
Anyways, try reseating cable connections first.
September 11th, 2007 at 11:35 am
Hello… I have a dell latitude CPx laptop wtih the problem you described. The screen is still working but I can see only a very dull image. I do not find the lid close switch where you said it was. There is not any button close to the LCD screen, but the power button. Oh, this problem began when the laptop, into its briefcase,fell to the floor and slightly hit its back. Maybe is anything broken in it, like the backlight lamp or the video cable? I have not opened the laptop.
September 9th, 2007 at 5:24 pm
Angelos,
You’ll have to remove the LCD bezel as it shown on the pictures. In most cases the screen inverter is located under the screen. All you have to do - unplug cables on both ends of the inverter board and install a new inverter. You can search for a new inverter here.
These laptop disassembly manuals can be useful.
September 9th, 2007 at 8:12 am
Hey Dude! I have problem with my monitor! My external monitor works fine so it’s possible a problem with back light! I press the lid switch and just for a piece of second turns on as you said so probably the switch has no problem. Sometimes it turns on just for a few seconds so I suppose that there is no problem with thee lamp. So I again uppose that it is a problem with the inverter. Could you tell me how can I open my monitor to change the inverter and an idea on how much this could cost?
Thanks again friend.
Very good post…
September 7th, 2007 at 7:34 pm
Dude you rock… I did as instructed.. works like a charm… it was only the switch. Thank god but none the less.. my sony is back up and runnin