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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February 2nd, 2012 at 8:59 am
@ Kevin,
Does it go to sleep mode when you close the lid?
Try this. Unplug the AC adapter and remove the battery. Now try turning it on normally. Does it have backlight now?
February 2nd, 2012 at 8:31 am
@ Igor,
I cannot tell. I don’t know voltage specs for all laptops.
What is the problem? There is no image at all? Or the image is very dim? Can you get image on the external monitor?
January 31st, 2012 at 7:39 pm
Hi,
I read all the problem & comments above, but none the same to mine. My laptop screen wont display at initially, but after 30 to 45 minutes its display normal. What went wrong ? any idea?
sazcole
January 28th, 2012 at 10:38 am
Hi,
I thought I had a bad inverter on my 6 year old dell Inspiron b130.
So I ordered a new one and after replacing the old one my screen was working again and for a few hours that I worked on laptop, it was just great. As I shut the laptop (just folded shut) as I always do, next morning I had black screen again. Any wisdom and or advice would be greatly appreciated. Thank you, Kevin
January 26th, 2012 at 11:36 am
Hi, i dont know the right sequence wich goes to inverter,but first one mine color is blue has voltage 19v. but it is your last if we will lok on your picture. An one more wire has 3v voltage is this Ok or my motherboard is damaged. My laptop is Hp 6820s . Tnx on answer,and sory on bad english.
January 22nd, 2012 at 4:49 pm
Your test method, while as good as my research has found, is not 100% reliable.
Example: failing, or intermittent inverter. Backlight lights for several seconds then turns off. Tested with lower power consuming CCFL. stayed lit = bad CCFL.
Not true – reconnected to laptop with inverter hanging loose and laptop worked perfectly for several hours. Mounted inverter and Backlight failed again.
Inverter is defective. Stress cracked trace or cold soldier failure.
December 28th, 2011 at 11:02 am
@ Fabiog,
If both inverters are identical, you can try it.
If inverters are different, I wouldn’t do it. You can damage the inverter or kill the motherboard.
I would suggest buying a new inverter. They are not expensive.
December 28th, 2011 at 5:38 am
Is it possible to test inverter with another one with the same connectors even though different reference.
In my case an Acer inverter for 15.4 to be used on a toshiba 15.4.
Is there a chance the acer or Toshiba one will be killed
thanks
December 27th, 2011 at 8:47 am
My laptop working good but when i put down my lcd screen on working period,windows goes on standby mode and when i active my windows a fatel error comes and laptop gone restart.what’s the problem in my laptop guide me.
thank’s…
December 26th, 2011 at 2:39 pm
@ Amathanio,
The backlight lamp needs very high voltage. The inverter outputs probably 1000-1500V AC. You CANNOT use a LED for that.