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 20th, 2009 at 1:30 am
Be for this post i have no idea regarding how to open LCD screen and make repairing of LCD screen .You provide very nice information and fantastic things.I am really glad about this.
November 14th, 2009 at 10:13 am
Sweet! I went ahead and tried again and got to all the wires. Disconnected the wires and made sure the monitor cable was connected firmly, and now it finally works again.
Thank you~
November 13th, 2009 at 4:36 pm
Duane,
You’ll find my laptop disassembly instructions at http://www.irisvista.com
You can use instructions for a Satellite A215, it’s similar or at least very close to Satellite A205.
Could be bad connection between the video cable and motherboard. Try reconnecting the cable.
Also, could be defective video cable.
November 13th, 2009 at 4:06 pm
Tamal,
It’s hard to tell without testing the laptop with known good spare parts, but I think this is related to the CCFL.
From my experience, when inverter fails the entire screen goes dark.
The inverter either works and provides power to the backlight lamp, or doesn’t work and the backlight gets no power at all.
I think the backlight lamp goes bad.
November 13th, 2009 at 3:00 pm
I was given a laptop to check out since the monitor was not working. A month ago I concluded the monitor was just shot and needed to be replaced as I was able to get video to an external monitor but got no image on the LCD at all.
TodayI decided to break it out again to use with an external monitor. But this time I noticed if I pulled the monitor from the top forward (i.e. I pull it as I might close the laptop, But only pull enough until I lose the “slack”) I was able to see the monitor display without the back light. Once I let go, the image disappears. Then if it’s played around with in some other random fashion, I can get the display and back light to work.
I am wrong to assume that I may just have a wire problem and not an inverter or backlight issue? I took the laptop apart, but I just couldn’t figure out how to get the monitor off so I could take the bevel off it.
Laptop is a Toshiba A205-S5871.