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 2nd, 2008 at 4:02 pm
I’m having similar problems as described by the many replies herein. My screen initially went black about two months ago. I could still see the image if the light in the room was turned on, and connecting my laptop to the TV produced a perfect image. Opening and closing the lid would bring the picture back, but only for either a split second or, at most, two or three seconds. Then, about a week later, I opened the lid one morning and the picture stayed on for maybe four or five days! This cycle repeated itself for the next few weeks. (It should be noted that during the periods when the screen stayed on there would sometimes be a slight flickering effect.) So I ordered a new inverter. The website I ordered it from did not have the exact part number I needed, but it did offer an inverter that was compatible with the part number of the original. After replacing the original inverter with the one I purchased, the longest the screen lasted before going black was maybe 30 seconds, AND I heard a buzzing noise that I did not hear with the original inverter. So I put the original inverter back in and for whatever reason the screen didn’t black out once for a good three weeks. Well, for the past week the screen is going black again. Opening and closing the lid did very little until I figured out that if I pressed my finger once into the screen bezel directly over the invert and then closed and opened the lid, the screen would stay on for hours at a time (in some instances, a day or more!). However, there was a new wrinkle: manually adjusting the screen’s brightness directly affected when and how the screen would go black. Adjusting to the dimmest screen setting would eventually result in screen flickers that, after a few seconds, would lead to the screen going black. Adjusting to the brightest screen setting would result in normal image functioning. This lasted three days. Now the screen is going black again. Opening and closing the lid produces an image for a few seconds, except now the left half of the screen is very dark while the right half looks normal. And the kicker: When I switch the original inverter with the one I purchased online, the entire screen lights up like normal but will still go black after 2 – 10 seconds go by.
So does this sound like a backlight issues (I have dual lamps)? Does it sound like I should try finding an inverter with the same part number as the original even though the one I purchases should have been compatible? Is it possible the one I bough online is faulty? Any suggestions would be supremely appreciated!
By the way, my laptop is an HP Pavilion dv9000.
October 6th, 2008 at 2:17 pm
Hello,
I could use some advice regarding a failing LCD backlight. I have an Acer Aspire 9800 with the following behaviour:
- The backlight flickers and eventually turns off.
- Re-opening the lid makes the backlight fire off again, failing in a few seconds.
- Manually turning off the backlight ( fn + [F6] ) and back on again doesn’t make it fire off again.
- Reducing the backlight power ( fn + [left arrow] ) makes the backlight last longer, for an hour so far. The flashes, however, continue and some of them are brighter than the screen should be. (Ignore that, it lasted for over an hour now, flashes disappeared)
- Ofcourse, the LCD keeps showing a picture or else I wouldn’t be rambling about the backlight.
- When the backlight is on, the LCD displays a proper image, not pink or reddish which in my opinion would exclude the light bulbs.
Now by what I’ve seen and read I suspect a failing inverter. However, I could use some advice.
Could it be the power supply is failing; delivering insufficient power causing the backlight to “magically” turn off.
Could it be the lid switch? It’s a magnetic, not mechanical and I have no clue on how it works or whether it could cause the behaviour described above.
While I keep my bet on the inverter, any comment on this would be appreciated.
Sincerely your,
Eric
PS.
Food for thought:
Could a failing power supply cause this issue, with motherboard capacitators preventing any other clues from surfacing?
Why does the “mechanical” switch (magnetic in this case) have a different effect on lighting up the screen than the software switch ( [fn] + [f6] ). Does the inverter have some kind of build-in protection? If so, what could be triggering it in this case?
October 6th, 2008 at 10:29 am
Impressive site! I’ve got an asus s5a 12.1″ laptop, and my backlight falls out when I tilt my screen to far backwards. First the light on the left side goes out, then if I continue to tilt, also the right light goes dark. Do you have any idea where to start..? Thanks!
October 1st, 2008 at 12:26 pm
I have an HP ze 5700, the screen kept blinking and finally failed. I installed a new inverter board a few months ago and it still blinks white with the background still there. Do I have a backlight promlem and how much is a new one.? I’m not very good at this and I dont want to spend a lot of money unnecessarily. I’m just a retired person.
September 27th, 2008 at 7:15 pm
Ratha,
Could be connection related problem. Check the video cable, make sure it’s properly connected to the motherboard. Try reconnecting the cable.
September 22nd, 2008 at 4:44 am
I had a power pin fault (had loose connection with board circuit) and managed to fixed by removing the board and rejoined with soldering iron. then it works ok but the lcd display became blinking and then turned into negative film like colour (like a film negative shading-no original colour), some times turn to normal then go blinking…. like over lightening or bright light is over the normal screen.
But the blinking of the display is still have problem. When the cool environment, it has small blinking but without external table fan cooling and opened with lot of applications (AVG scanning, firefox, ms word), it has frequent blinking.
First i faced the problem when i tried to install the MS Powepoint 2007. then i stopped to install it.
Specifications:
laptop: toshiba tecra 8100
OS : Windows xp
Speed: PIII
RAM : 256
please help to solve the problems.
thanks
ratha
September 21st, 2008 at 11:24 pm
Bruce,
The only way to find the culprit is installing known good parts. I’ve been trying to find a reliable way to test inverters with a multimeter, but haven’t found it yet.
The only reliable way I know is swapping parts.
You cannot use this troubleshooting method to test inverter/backlight.
Could be:
1. Bad inverter (more likely).
2. Bad backlight lamp (less likely).
3. Motherboard problem (rare).
4. Video cable problem (rare).
From my experience, inverters fail more often than backlight lamps. I would try replacing the inverter board first.
September 21st, 2008 at 1:34 pm
cj2600,
Thanks. I did find one website that lists my make and model laptop with the compatible CCFL and the price is under $15.
However, I do not know how to determine if I need to replace the inverter board (easier looking job for about $45)… OR, if I need to replace the CCFL bulb.
How can you tell?
I can output my laptop screen very nicely to my TV screen and the computer works just fine.
So, in remembering what you taught was the purpose of the inverter board – that I believe is my prime suspect – because the screen went out completely without a long death period of that pinkish look.
September 20th, 2008 at 10:07 am
Bruce,
It’s possible to replace just the backlight lamp as I did in this post:
How to replace laptop backlight lamp (CCFL)
It’s not easy and the backlight replacement procedure requires a lot of patience and concentration.
You can easily damage the screen but on the other hand, you can fix it for under $15.
If you know for sure that your problem is related to the backlight lamp and not to the inverter board, you can try replacing the backlight lamp.
September 19th, 2008 at 3:07 pm
Last night, shut the top for the evening and this morning opened it to find a very very very dark screen. The display never recovered. However, with a flashlight you can see that the computer is functioning just fine. Its too weird peering into your LCD with a flashlight and seeing the image ’somewhere in there’.
Inverter board or back light? Plugged the video output into the TV and got my desktop just fine (but its not a HDTV so the quality was crap). Ok, there’s a screen in there – but its like looking into deeply smoked glass.
My Service Manual shows an inverter board and a display assembly in the exploded parts view of the unit – but no back light or bulb? Customer service online chat just told me I needed to replace the display assembly part … but yikes! that is the entire LCD screen kit and kaboodle! Huge price difference between CCFLs and display assemblies!!!
Any comments? Do some laptops have the backlight as a component of the display assembly so your stuck buying the entire set??