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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September 20th, 2009 at 8:08 pm
Jesse,
It’s possible but not very likely.
1. There is a chance that one of the new parts is defective.
2. You didn’t connect them properly. Try reconnecting parts.
3. If you replaced both but still experiencing the same problem, it could be related to the motherboard. I cannot tell what is wrong without looking at the laptop.
September 20th, 2009 at 7:49 pm
waligi,
1. I would test the power adapter. Maybe the adapter is dead and the battery doesn’t have enough power to start the laptop.
2. Check memory modules, make sure they are properly connected to the motherboard. Try reconnecting memory. Try removing modules one by one and test the laptop with one module at a time. It’s possible that your problem is related to memory.
September 20th, 2009 at 4:58 am
Hi everyone,really need help with my compaq MA8.
when turned on,nothing appears on the screen and the touchpad lights up only for a few seconds and then goes back off.After that,nothing happens and any key combination given does not even give the usual beeps after.
I would appreciate any suggestions,thanks
September 18th, 2009 at 10:07 am
Could the bulb and the inverter board go bad at the same time?
I sent the new inverter board back and ordered a new LCD screen. When I put the new screen in it’s still dark! I’m guessing they were both bad and now I’ve got to reorder the inverter board…
Thanks for your help!
September 17th, 2009 at 5:45 pm
I have a similar problem with my Desktop LCD, a LCD Flatron W2242T.
The bottom half of my screen is dark and has light spots right at the bottom, whereas the top half works perfectly. I was considering buying a new screen which wud set me back $300 = =”
but this site has given me hope, maybe i have a faulty backlight at the bottom. Any advice on what i should do?
thanks guys
September 7th, 2009 at 3:22 am
Hi, I have a problem with a laptop, Dell D830 when I turn it on, the screen brightness is ajustable with “Fn key” at night is OK but at day the brightnes is to low. How i fix it???
September 2nd, 2009 at 12:39 pm
I have replaced the lcd and the inverter on a gateway mx8738. I am going to try the multimeter test later this evening to see if the inverter is getting power. My screen now will only show a faint image. I dont have a lid closed switch, but was wondering if this computer has a magnetic switch and if so how would I test it or find it? I have also changed the lcd cable out but still nothing. When I boot the computer without an inverter connected at all it does the same thing as if it was connected and bad, dim screen. Any other things I should check before parting out this laptop?
September 1st, 2009 at 4:24 pm
Hi!, i got a problem like that
I have an Acer X193w and it turn normally but in 2 seconds the light turn Off and i can see the image, its kindda screensaver..
can you help me?
PS: sorry about the bad english bro
Thanks!
August 26th, 2009 at 9:31 pm
mauricio,
Can you see a very very dim image on the screen when the backlight is off? It’s possible you have a faulty inverter board.
I do not understand this part of the description. The external monitor turns brown?
August 26th, 2009 at 9:25 pm
AL POE,
I’m discassing LCD failures in this post. I think your failure is similar to the example 7.
I would say you have a faulty LCD screen and it has to be replaced. Apparently there is a bad solder joint somewhere on the LCD controller board and when you apply some pressure on the screen you temporarily fix it.