In this post I explain how I test the LCD screen inverter board in a laptop computer.
The screen inverter failure is very similar to the backlight lamp failure. In both cases the screen gets very dark and the image on the screen becomes very faint, barely visible under a bright light.
If you suspect the inverter board failure, I know only one reliable way to test that. It’s either replacing the inverter board with a known good one and see if it works, or connecting a known good backlight lamp and see if your presumably bad inverter lights it up.
In most cases I go with the second method – testing the laptop with a known good backlight lamp. Why? Because backlight lamps are pretty much universal. The same backlight lamp will work with many different inverters as long as they have matching connectors. I’ll talk about these connectors later.
The inverter board is located inside the display panel under the LCD screen. In most laptops you can access the inverter board if you remove the LCD screen bezel. The inverter board has connectors on both ends. The left side of the inverter is connected to the LCD cable. The right side of the inverter is connected to the backlight lamp which is mounted inside the LCD screen. Check out this display diagram.
To make sure that inverter board is getting power from the motherboard (via the LCD cable), you can test it with a multimeter. In my case I connected the “+” lead of the multimeter to the pin 1 on the connector and the “-” lead to the ground trace around the screw hole. I got about 19.4V DC on that side of the inverter, so it’s getting power from the motherboard.
WARNING! If you accidentally short something on the inverter while testing it, you can damage the inverter or even the motherboard. Proceed on your own risk! Not sure? Don’t do that!
So, the inverter is getting power from the motherboard, but the screen is still dark. Apparently, it’s either bad inverter or failed backlight. Let’s test it with a known good backlight.
Here’s what I’m going to do:
1. I will unplug the LCD screen from the right side of the inverter. Basically, I’m unplugging the LCD backligth lamp which is located inside the screen.
2. I will plug in my known good backlight lamp which you can see on the picture below. Please notice that my test backlight lamp is shorter than the screen, but for the test purpose that’s OK.
Results I’m expecting:
1. If my test backlight lights up, the backlight lamp inside the screen is bad and there is nothing wrong with the inverter board. If that’s the case, you’ll have to replace the LCD screen or replace the backligth lamp (which is not easy at all).
2. If my known good backlight lamp stays dark after I turn on the laptop, most likely we have a faulty inverter board. If that’s the case, you’ll have to replace the inverter board and it’s relatively easy.
There are two different types of backlight connectors, you can see them on the picture below. The top one (big) is not as common as the bottom one (small). I do most of my test with a backligth lamp which has a small connector.
IMPORTANT! If you decide to buy a new backlight lamp for test, you have to make sure that the connector on the lamp matches the connector on the inverter. Very often backligth lamps are sold without any wires attached. If you plan to use this backlight as a test equipment, you’ll have to find one with wires as I have on the picture 3.
You can buy a cheap backlight lamp with wires here.
Finally, when you ready to test the laptop, unplug the LCD screen from the right side of the inverter.
Plug in your test backlight lamp and turn on the laptop.
In my case, the backlight lamp lights up, so the inverter board works properly.
Check out my previous post about troubleshooting laptops with backlight failure.
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November 13th, 2009 at 3:02 am
Hello. My notebook Samsung R50 has its some left portion of it more darker than the rest of the LCD screen. And overall I have also noticed that my 3 year old this notebook of mine had its overall brightness reduced.
My question is: is it the CCFL needs to be replaced or is it the inverter gone bad?
November 6th, 2009 at 10:32 am
faysal,
I don’t think so. If the screen lights up the inverter is working properly.
I guess you are missing a piece of software controlling the Fn key.
November 5th, 2009 at 8:17 pm
Thanks,
No im not installing factory drivers i have to find out then istall all
i want to ask that this keys are not working because of new invertor ? or some driver problem ok first i intalled drivers then lets see it is enable or not.
Thanks a lot again
Faysal
November 5th, 2009 at 12:04 pm
Boss,
from where i can get the company service manuals and repairing guide with flow chart for laptops of all brands, pls help me
November 5th, 2009 at 11:34 am
faysal,
I’m not sure why the Fn key doesn’t work. Did you reinstall all factory drivers and software after installing XP? You can install it from the CD or download from Dell website.
November 5th, 2009 at 4:17 am
Hi i am facing a problem i installed new invertor in my dell laptop decause of old one is not working but my display keys function i,e Fn + Arrow keys not working i also fomate my hard disk with new partition installed Windows Xp.
Pease help me how i can enable Fn keys funtions.
Quick response highly be appreciated.
Thanks
November 5th, 2009 at 2:46 am
Just to say abig thank you for putting this up, I thought it was excellent and it has helped me in resolving the issue of the backlight I have with my Toshiba Equium Laptop.
Props to you.
Dave
October 25th, 2009 at 10:17 pm
antoine,
Most likely the pinkish screen is related to the backlight lamp failure, not the inverter failure.
October 18th, 2009 at 5:15 am
Great site!
I have a related problem with my 5 year old dell latitude d810. The screen is now dark and the image on the screen is barely visible but still working. Everything else works fine. Shortly before this problem, the screen started to flash when I opened windows or was slightly pink. Your site (and others) seems to indicate that this may be the inverter or the back light of the lcd. I have looked at your other post on the backlight, but does the way the problem occurred tell me something informative about its cause?
October 16th, 2009 at 4:37 pm
Great site!
I have an HP ze5478cl. the lcd works for a minute goes grey then rolls like an old tv set with vertical hold problems, then comes back. it works fine with an external monitor.
so , my question is…LCD? Inverter? backlight? which is bad?
Thanks, Ron