Do you have a problem with the backlight on your laptop? If yes, you are not alone, that’s one of the most common laptop problems. In most cases the screen inverter is the culprit. Here are some LCD screen backlight failure symptoms that could be related to a bad inverter board:
- Laptop boots as usual but after some time the screen blacks out. You still can see an image on the screen but it’s very dim. You might even use a flashlight to see it better. Sometimes the backlight comes back for a while but then goes off again. In some cases you can turn the backlight on if you tap rapidly on the lid close switch.
- The screen always stay black and the backlight never comes on but you still can make out an image on the LCD. It’s dark, but the image is still there.
-In some cases you might hear a buzzing noise coming from the area where the inverter board is located, it’s on the bottom part of the display assembly.
NOTE: if you cannot see an image on the screen, most likely you have a different problem and there is nothing wrong with the screen inverter.
Other related articles:
Laptop has bad video on the LCD screen. What is wrong?
Notebook display assembly diagram. How image appears on the screen.
How to troubleshoot and fix laptop video problems
How to replace laptop backlight lamp (CCFL)
Here’s an example of replacing the FL inverter board on an IBM ThinkPad T41 notebook. This guide will work fine for any other IBM notebook. Replacing screen inverter on other notebooks like Dell, HP, Toshiba, etc… will not be much different.
First of all, unplug the AC adapter and remove the battery.
In order to access the inverter board you’ll have to remove the LCD screen bezel. On most laptops screws are hidden behind screw seals. In this case we have 5 screw seals on the front. Carefully remove the seals with a sharp object and glue them on the LCD bezel, in this case you will not lose them. Remove all screws and mark them somehow so you are not confused when you assemble the notebook back.
Some laptops also have screws on the side of the display. This notebook has 3 screws on each side. Remove screws seals and then remove screws.
Start removing the LCD bezel with all fingers. Carefully wiggle the bezel to release plastic latches. Never use any sharp object during disassemble because you can accidentally damage the screen.
If latches are very tight you can use a guitar pick to unlock them. Insert the guitar pick between the LCD bezel and cover and carefully move it alone the side.
This notebook allows you to replace the inverter board without removing the LCD bezel completely. Lift up the bottom part of the bezel and remove one screw securing the inverter board to the LCD cover. This location is very common for the screen inverter. On most laptops you’ll find it under the display bezel below the screen.
Carefully lift up the FL inverter and rotate it a little bit. Unplug cables on both sides. The left side of the inverter board connects to the video cable, the right side to the backlight bulb (CCFL tube) inside the LCD screen. Remove the inverter and replace it with a new one.
To find a new inverter board (and any other spare part too) for any IBM notebook you should use the FRU number from the part.
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May 8th, 2007 at 3:20 am
CJ,
Thanks for the info. Looks like a job for a professional. Unfortunately, I don’t have any test parts. I am thinking the best, easiest & most practical fix for me is a brand new LCD screen. I’ll keep the new inverter since the old inverter is 3 yrs old & used approx 4 hrs a day average.
How easy is it to replace the keyboard? The most used letters have worn – no big deal but if I am going to replace the LCD I might as well replace the keyboard also. But, I don’t want to open a pandoras box and because of my inability, cause other problems. What’s your opinion?
Thanks again for your speedy reply!
May 7th, 2007 at 10:12 pm
Rory,
Yes, it could the the bulb. Unfortunately there is no simple answer because you might have a bad bulb, defective video cable or faulty motherboard. The only way to find out is installing a test screen or connecting a known good backlight bulb. For cases like this I always keep 2-3 different backlight bulbs I removed from broken screens, it makes my troubleshooting process much easier.
Is it possible to replace the backlight bulb? Yes it is but I never done it myself. The backlight bulb is buried deep inside the screen and replacing it is not an easy job. Here’s an example of replacing the backlight bulb on an IBM laptop.
BTW, check the lid close switch – small button located close to the hinge. Make sure the switch is not stuck inside. If the switch gets stuck inside the case, it cuts off power going to the backlight bulb and it stops working.
May 7th, 2007 at 7:00 pm
another dark screen question….
I have a 3 yr old Toshiba Satellite Model A20-S207.
It’s been a great laptop until last week then the screen started flickering and finally went really dark and dim. With some research on the web, I thought it was the FL inverter. I found a new inverter, replaced it & the screen is still dark.
Could it be the bulb? If so, how & where do I find the bad bulb? Is it a replaceable item?
Thanks!
May 4th, 2007 at 11:20 pm
@cj2600
Hi thanks for the reply; I was getting itchy feet and decided to go the whole distance with the “Blackness” on LCD issue…
I re-sat all connectors to the LCD and Mobo, still nothing; the cable was fine so I forked out £87 for a new compatible LCD – 5 mins of fiddling later we had lift off.
First time I’ve come across this particular issue, the fact all the backlights were in full swing swayed me to the LCD.
Can’t complain – got a new laptop for £87!
April 24th, 2007 at 10:23 pm
Chris,
If you can change the brightness of the black then I assume it’s not an inverter problem.
If I understand right, you have the following symptoms.
1. The screen is blank but it’s not completely dark, you still can adjust the brightness of the backlight (inverter and backlight lamp are OK).
2. There is NO video on the laptop LCD, not even a faint image.
3. The laptop still works with an external monitor (probably the motherboard is OK).
Is it close enough? If yes, then the LCD doesn’t get data from the video card.
First, I would try reseating the video cable on both ends – on the motherboard and on the LCD screen too. It might be just a lose connection. If it doesn’t help, I would probably replace the video cable, it’s the less expensive part. If replacing the video cable doesn’t help either, you have either a bad LCD or a faulty video card (probably integrated into the system board). In this case you’ll have to guess witch one is bad.
Ideally, you just connect a test LCD and this test helps a lot. Unfortunately not everybody has a spare LCD at home.
April 24th, 2007 at 10:02 pm
Allan Johnston,
The wireless antenna is not just a pair of wires. There are square plates attached at the end (I believe it’s for better signal reception). Take a look at the step 8 of this Satellite M45 teardown guide. Do you see two yellow squares on the top of the cover? That’s what I’m talking about.
I’m not sure how you can connect an external antenna to the internal wires. Please let me know if you find the solution.
April 24th, 2007 at 6:25 pm
elkyn,
That’s a good question and I wish I know the answer.
When you start the laptop, do you see any activity at all or it’s completely dead? Check the memory module, try moving it from one slot to another. Test the laptop with an external monitor and see if you can get any external video. If the laptop works with an external monitor but you have NO video on the LCD (not even a faint image), try replacing the video cable. The video cable is not expensive but might fix your problem. You can find it for $15-20 on eBay, make sure you are buying a correct one. Check the FRU part number on your cable and buy the same.
April 23rd, 2007 at 11:31 am
Hi there, I got a laptop that works fine using the external VGA D-SUB, but when trying to use the laptop without the display is just black – nothing but blackness.
The strange thing is, I can actually change the brightness of the black…
Any ideas? Is this the inverter or you reckon it could be the LCD itself?
Appreciate any help guys!
Thanks
April 23rd, 2007 at 5:27 am
I have an M45 Toshiba. Is the wireless antenna just a pair of wires or is there something else at the end of the wires. I don’t want to take the unit apart to find out and I want to hook into the wireless pcb so I can use some sort of external antenna (parabolic).
Any suggestions are welcome.
April 22nd, 2007 at 9:49 pm
Jacin,
Even though the screen is dim, I assume you still can make out an image on it, correct?
1. Try reseating the video cable connector on the motherboard
2. Make sure the lid close switch isn’t stuck inside and moves freely. Try tapping on the lid close switch and see if the backlight flashes when you do that.
You can do 1 and 2 before you buy a new inverter.
If installing a correct inverter doesn’t solve the issue either, then one of the following parts is bad:
- backlight lamp inside the screen (more likely)
- video harness (not very common but possible)
- motherboard (less likely)