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.
Also, you can read the following posts:
Troubleshooting laptops with backlight failure.
Laptop screen shows strange colors. What could be wrong?
How to troubleshoot and fix laptop video problems.
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December 30th, 2009 at 12:24 am
my toshiba laptop problems:
1) once the ac adapter was plugged in, the laptop screen was frozen with horizontal lines. cant move, cant shut down, no response to alt crtl del. But, if only use the battery without ac adapter, the laptop wil operate normally.
however, the battery only can use for 1 half hours. therefore, i hv to plug in the ac adapter. once plugged the screen was frozen with horizontal lines. cant move, cant shut down, no response to alt crtl del.
wat’s wrong with my toshiba laptop?
December 19th, 2009 at 11:17 am
I just replaced the inverter in my Dell 640m, and the display is still not working properly. It starts up, displays Dell logo, and then goes black. I can see a faint image on the display if I hold a flash light to it.
I connected an external monitor for now. When I use the keyboard to switch back and forth between the LCD and external monitor the LCD works for a few seconds, but is very pink.
Any thoughts?
December 16th, 2009 at 2:13 am
please write me back. my fiance just sent me this laptop from japan and the box was damaged and now i turn it on and it goes black BUT i just realized along with this website that if i push on the part of the screen where you show the screen invertor is, i can get the screen to flicker and dim back on. one side is bright and the other is dark… is it posible that this damage is done due to shipping? it wasnt wrapped or really protected. i cant believe the postal service didnt do anything to protect it. im going to take it in to be fixed, now that i know what is wrong and can help them out. i dont know much about computers, but i know how to figure it out and what to do .. but i wont do it myself. haha. i dont want to ruin it even more but please write me back!
December 10th, 2009 at 11:03 am
I have a sony vgn-nr38e, you can just make out the logo on start but thats it. I have tried changing the inverter and have pluged the screen in to another laptop to check the back light which is working fine too. Im at a bit of a loss to whats happening, any help would be great.
December 9th, 2009 at 7:34 am
It could be possible that the inverter was being overloaded with the extra current from the AC adapter. Laptops usually dim the screen when connected to a battery hence less current. Thats the only reason I could think of.
December 7th, 2009 at 9:01 pm
I had a Dell XPS 1210 for repair presenting following symptoms: when booting i could see the DELL logo but after the screen turn pitch black. After i’ve tried the laptop on an external monitor and the image was good, i opened the screen and tested the backlight(with an replacement inverter). It wasn’t working. I changed the backlight, it was working but ONLY WITH THE BATTERY. When i was pluging the AC ADAPTER i was getting the same dim pitch black screen…so i reached the conclusion that the inverter was bad…replaced the inverter also and everything was working fine.
Any ideea why the inverter was working only with battery and not with AC Adapter?
December 5th, 2009 at 3:42 pm
I’ve been having an LCD issue with my laptop as well CJ. Its a Toshiba Satellite M105-S3041. When I flip the LCD screen open it’ll be on from 1 degree all the way up to 15 degree, but after that it’ll turn off. I ended up opening to check the connectors, etc and everything seemed fine. I’ve created a video to show you the issue. The screen works perfectly between 1 – 15 degrees. The monitor output works perfect as well.
http://www.youtube.com/watch?v=9c8cvbiiBmY
December 5th, 2009 at 4:37 am
My daughters laptop hp pavilion dv6000 entertainment displays wavey colours/ smudge difficult to discribe but when i plug my desktop monitor in a get a great picture.
Iv bought a new screen and it looks just the same. Iv uninstallled and reinstalled display adaptors and all still looks the same.
Any thoughts please please please ??? Daz
December 2nd, 2009 at 3:02 pm
Dell inspiron 1000 screen blacks out when (even slightly) adjusting position of screen towards close or open. The HD LED and power LED stay lit. No HD spin or fan. 3-finger salute does nothing. Can only do hard shut down and power up to revive. I have no problem if I just touch or squeeze the display; only problem when pivoting on hinges or when shaking the desk enough to adjust the display’s position. If it’s open at 90 degrees, for example, and I then open it to 91 degrees or close it to 89 degrees, display and fan shut off. As if sleeping. I exposed the hinges and made sure the sleep switch is not being triggered. Could it be a short in the cable running from the system board to the display? if so, where to get it and how to replace?
I’d appreciate any thoughts before I send it to Dell hell (recycling center)?
Thanks
December 1st, 2009 at 2:33 am
I think I messed up my last post by trying to add your response to my original post. So here it goes again. I have taken out the CCFL light from the display panel, reassembled the laptop and tested the light. The CCFL lit up but started emitting a metallic sound and after a while went off. I tried it later again (the laptop is working with an external monitor and I left the front bezel out to have access to the inverter at will) and found that the CCFL did not light up nor was there any sound. Could you tell me what I should replace? The video cable has been unplugged from the system board and re-seated without any difference in the display; it remains blank. BTW, the first time I booted up the computer with the CCFL outside, a very dim screen appeared but not on subsequent boots. Please advise.