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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November 25th, 2007 at 6:12 pm
Mark LaTorre,
It’s very possible that there is connection issue between the vide cable and the LCD screen. I’ve seen this problem before. Reseating the video cable might fix the problem. You’ll have to take a look on the back side of the scree, that’s where this connector is located. Make sure the video cable is properly plugged into the connector on the screen.
November 25th, 2007 at 6:08 pm
Martin Ruge,
This sounds like a problem with the LCD screen, not with the video cable.
November 25th, 2007 at 10:40 am
I am guessing that there is a cable to the screen problem, my unit works properly using an external crt but even while connected to the crt my laptop screen showes a medium white background with no other images. I can increase or decrease the brightness of the laptop screen using the function keys but still there is no image at all on the laptop screen only a uniform smooth white glow.
E-Machines m5312 laptop about 2 years old
LTN154X1-L03 Samsung LCD
W-720 Inverter
November 17th, 2007 at 4:39 am
Dear all,
I`ve problems with my notebook-screen. It shows a vertical bar, within the bar the image is darker than on the remaining screen.
Does anyone have an idea if this is related to a broken video cable?
Martin
November 9th, 2007 at 5:46 pm
I get the buzzing sound coming from the inverter and if I turn the brightness up the screen goes black and the buzzing stops. after it being on for awhile the left side of the lcd is slightly more dim than the right. external monitor works fine. Do you think its an inverter or bulb and if its the bulb where would i find one (inspiron 9400 – true bright screen) i found the inverter on ebay but can’t seem to see any bulbs maybe i’m not searching right. I want to know which it is before i shell out the money thanks
November 4th, 2007 at 10:48 pm
Angelos,
Yes, you can if the bulb comes with wires so you can connect it to the inverter board. The metal part is just a reflector.
November 2nd, 2007 at 2:23 pm
Can I test a backlight bulb directly after buying without opening the whole screen?I mean can I connect it dirrectly to the inverter without the metal part for testing first and if it works then replace it?
October 29th, 2007 at 11:24 pm
Tonight my Thinkpad 600X had a unlit screen.
Last night it was fine.
Backlight lamps look wickedly hard to replace but cheap on ebay. Inverters easier but not cheap. A new LCD, more than the whole laptop is worth.
Your suggestion to check the screen close switch – pure genius! You Rock.
October 25th, 2007 at 9:10 pm
Dj, Angelos,
If the inverter you installed is good, then my next guess would be the backlight lamp.
October 24th, 2007 at 3:55 am
Finally, I replace my inverter and like previous guy said it worked for 2 seconds with a strange noise from inside and then again the same problem (a faight black image without noise). Maybe this helps about my problem? Thanks again.
Angelos