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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July 19th, 2009 at 5:21 pm
About the only things that can cause inverters to fail are the power supply (as in, the power supply voltage to the inverter is too high, or has “spikes” on it which harm the inverter, etc.)and the CF light tube. I would suspect the light tube, to be honest, before I would suspect the power supply problems.
Oh, one other thing I just thought of: have you checked the inverter(s) to see if the input fuse is “blown”? You would check them with an ohmmeter; if the fuse is good, it should read less than one ohm. If bad, it will read a very high resistance, or at least, more than a few ohms. Some of these fuses are made with a chemical process, rather than being just a thin wire in a package. The chemical fuses tend to fail gradually if they are run near their maximum rating. If you have a situation where, say, an aging CF light is drawing a lot more power than it should, causing the inverter to work hard, it is possible that the chemical fuse could gradually age and develop enough resistance to eventually fail, gradually decreasing and then finally cutting off power to the inverter. These fuses are usually small, rectangular packages which look very much like an SMT capacitor. Look for tiny letter markings stating the rating in amps and volts, such as: 4A 27V . Or something similar. The inverter draws a lot of power (that is why it runs down the battery so quickly!), which means the components are under a lot of strain, which invites failures.
The inverter in my laptop has recently failed; it has a 4 amp chemical fuse on the power in line! It is “blown”, but there are other problems, so I will just buy one on ebay, where they are MUCH cheaper, rather than try to fix the inverter when I don’t have a schematic or part numbers.
July 17th, 2009 at 7:48 pm
Yes, when the problem first started I inspected the little switch because I had the same thought as you. However, the switch is in perfect shape and appears to be working just fine. Is it possible for some other faulty part inside the LCD to damage the inverter? I’ve searched the web and I really can’t find any other mention of someone having a similar problem with inverters getting burned out over and over again.
July 16th, 2009 at 5:14 pm
This may seem ovbious, but make sure that the switch which is pressed down when closing the laptop cover is not being held down by any obsticle. I say this because that is what happened to me. I laptop became a brick for a week or so until i decided to replace the invertor from another broken laptop only to figure out that the clips which keep the screen closed were broken and lodged in the switch which prevented the backlight from working. I am glad i didnt have to pay money for something i didn’t need yet spend time figureing out the little problem.
July 13th, 2009 at 5:47 pm
Here is a strange one. I have an older Thinkpad T21. For some reason it keeps burning out LCD Inverters. I’m on my third one. When I first replace it, the display works for a while. Within a few weeks I notice a delay from when I power up the laptop until the screen lights up. This delay keeps getting longer and longer until eventually it stops working all together. It starts at just a few seconds and over time becaomes a few minutes. Eventually, the screen just stays black. Each time I replace the inverter the process starts all over again. Once the screen lights up, it is rock solid. I can rock the lid back and forth with no flickering or anything like that so I don’t think there is a wiring problem. Any ideas?
July 13th, 2009 at 7:37 am
I have a HP Omnibook 900 and the backlight chip is broken. If I can find the right amount of voltage to put in, I can make it work! BUT I CAN’T FIND THAT! Please help!
July 9th, 2009 at 12:23 am
I have an HP NC6400, that was dropped and the LCD physically cracked. I took the opportunity to upgrade the screen from 1280×768 to a 1440×900, I installed the new panel, turned it on, the backlight came on fine, but, no video. A query to the supplier generated a question that threw my off balance, “Did you talk to HP asking them if inverter is compatible to new resolution?”. It would be my judgment that, if the backlight works, then the inverter is “compatible”, since the external VGA functions its my guess that the signal cable was also damaged in the fall, am I off base here or does the supplier have a relevant question?
July 1st, 2009 at 6:27 am
hi i would just like to ask, because i have the same problem, but not on a laptop. but on a IBM POS system. The lcd is fru 47p9282. i can see an image but very dark and no backlight. can you help me pls? thanks.
June 30th, 2009 at 4:29 am
Hi
yes, the external monitor showed perfect image, so I changed the LCD screen in the laptop so now it’s OK. I just wasn’t sure about which component to change (inverter or LCD).
So if backlight OK + external output OK = LCD error
Many thanks for the help and instructions
June 29th, 2009 at 1:13 pm
Thank you for this tutorial. The screen on my HP 6000 laptop was intermittently dim, so after reading your article I ordered a replacement inverter on eBay for less than $12, including shipping. I followed another website’s specific bezel removal instructions for my screen (trivial, if you know where the 6 screws are), and in less than 30 minutes I had a nice, bright good-as-new display.
June 28th, 2009 at 10:17 pm
Paul Volker,
I think it’s possible that you got a bad one. Try replacing it again.