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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August 22nd, 2010 at 2:30 am
I have a Lenovo 3000 N200 Model 0769 AUU
At startup the monitor has taken to randomly flickering or blacking out for a second and then working fine after it would appear to have warmed up. When I connect a remote monitor to it and run both monitors the remote does not flicker, only the LT’s monitor. The display driver is up to date as is Vista.
I am suspecting that the LCD screen is going bad but wonder if there would be anything else that would be causing that issue?
Thanks
August 19th, 2010 at 3:02 pm
Great tips, but I tested the power from the motherboard and I only get 3.5v from about the thrid pin on the connector. I cannot get the 19v from the board to the invertor. What would be causing this?
August 19th, 2010 at 3:59 am
Just installed a brand new screen in my Sony Vaio pcg-8v1l. I have installed dozens of screens over the years and had no issues. On this install, it all went fine until I booted up.
On boot the Windows Logo and Login Buttons are all set to the right. When logged in, the Start bar across the bottom is about 2 inches below the lip on the display. In other words, I can not see it. I can paly around with the mouse and get to the bottom and start it, but when it pops up, I can only see the top half of the pop up menu. Can’t get to programs, control panel nothing.
Not sure what to do here. I checked all of the drives and they are up to date. I ran the Nvidia wizard and it is all correct. Changing screen resolution does not help either. Any ideas. All I did was replace the screen, nothing else. Could it be the Screen Inverter?
July 31st, 2010 at 1:47 pm
I replaced an obvious broken LCD screen in a my Hp Pavillion 1285DX, but got no picture once all wires were connected. I was ready to replace the inverter, but it turns out the LCD ribbon cable was not making good connection even though it appeared to. It’s working fine now.