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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January 26th, 2009 at 9:52 pm
Vir,
From this description it sounds that you have a problem either with the inverter board or backlight lamp. I cannot tell which one is causing the problem because both parts fail very similarly. The inverter would be my first guess.
Why not? If it works, it works. Maybe it was just a connection related issue and reconnecting the cable fixed the problem.
If it fails again, I would try replacing the inverter first.
January 25th, 2009 at 10:44 am
Hi, I found this site exremely intersting, making the complex world of laptops a tad easy. Coming to the issue of laptop display, Im facing some issues myself. The laptop display is dim, which happens a few secs after booting. It is very hard to make out whats on the screen. But the problem always occurs a few secs after booting, its perfectly ok before that. Dislay is fine on an external screen.
I went throught the site checked out the inverter model I had. I’ve put the old inverter back. Booted again, somehow there were no problems this time. However, I don’t expect that to last too long. My guess is that its the inverter, but I’ll need to be sure. Hope someone here can give me few tips how to test it.
January 19th, 2009 at 1:16 pm
HI,
I changed the inverter of my Toshiba laptop 3 weeks ago, just after I changed the inverter the screen started to flicker, first I thought that the problem was with the new inverter but then I realized that was with the back-light.
It is possible to be the same problem that damaged the inverter and now the back-light or is just a coincidence or while I was changing the inverter I screwed up the back-light?
January 2nd, 2009 at 12:14 am
Hey guys
Ive justt recently been having troubles with my Toshiba Satellite m50..i have the same problem as the rest with my backlight..but it ocassionaly goes but then goes out after a while..ive unplugged an replugged the inverter thinking it could be a bad connection…any other ideas?? help would be appreciated thanx
December 26th, 2008 at 2:46 pm
Bryan Ard,
I have exactly the same problem as you on my toshiba m100. Have you found any solution of the problem ? it blinks slightly during startup and then once by the time the windows logo shows on. Will appreciate your help if you have any clue what the problem should be…
December 10th, 2008 at 12:47 pm
I have a similar situation. My screen does not light up but I can see the images very faintly. I am now working with a external monitor.
I replaced the backlight with a one that I got on ebay. I was actually a cracked lcd display. and I took the entire frame which had the backlight in it and replaced mine with it. I did this so that I would not damage the backlight trying to get it out of one frame and put it to another. After all this the screen was still the same. So is it the inverter ? If the inverter was faulty would it have burned the backlight? If its the case the one I replaced may have been burned as well. Do I need to replace both and see?
Thanks
November 27th, 2008 at 7:28 pm
i’ll be fixing my own HP laptop..
the problem was it has no display, which i realized, really has a backlight failure..
i tried it with an external monitor, it works. as if nothing hapeened.
i wonder if the real problem was not the backlight lamp..
will i replace the inverter board?
how much do you think it will cost me?
in philippine peso, if you may… i need an estimate…
November 18th, 2008 at 2:03 am
Thanks for setting up a help website. I was just wondering how you take the panel of where the backlight is. Im going to attempt to fix my laptop when i get home. cheers
November 3rd, 2008 at 7:58 pm
Great article! I tried an test inverter, no change, tried a test backlight. New inverter does nothing with new backlight. Old inverter causes backlight to blink briefly during startup then nothing. Anyone seen this before?
TIA!
November 2nd, 2008 at 5:00 pm
Paul,
Your problem sounds either like a bad inverter or bad backlight lamp. Unfortunately, the only way to find the culprit is testing the laptop with a KNOWN GOOD part.
Yes, it’s possible. Could be a faulty inverter or maybe it’s not compatible with your screen.
I would try installing a new inverter with the same part number. If you still have the same problem with the screen, most likely it’s bad backlight lamp.