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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October 5th, 2009 at 4:37 am
hi
dear
i study y r above page really very intrested
i have laptop reparing center here in my city
i have often needs for laptop ics for motherboard
reparing will y help me for my requrment of ics
and chip motherboard according requerment
thanks again and again for such a information
best regards
September 26th, 2009 at 3:04 pm
.
does inverter or the backlight problem cause your screen to be black permanently if not replaced?
I have a problem with my old laptop screen – sony grx series – that doesnt seem to turn on eventhough everything else seems to work fine. I can only get the screen to turn on only if i remove and reseat the ram or “shake” my laptop a couple of times.
is this indication of an inverter or backlight problem?
.
September 23rd, 2009 at 9:14 pm
:’( That is too bad… It is the most expensive part! :’(
Thank you very much for your reply. I now for sure know what to buy then. Thank you!!~
September 23rd, 2009 at 6:16 pm
hannahtuk,
It’s very common.
I don’t think that your problem is related to the inverter board because the rest of the screen is still bright. Apparently, you’ve damaged the backlight lamp inside the screen.
That means you’ll have to replace the screen.
September 23rd, 2009 at 10:47 am
I have a Dell Inspiron E1705 with an WXUGA+ display. I accidently closed the laptop screen cover when a pen was still sitting on the keyboard. Since then, about 1/3 of the screen (on the left side) is dimmed. It never gets really dark, but it’s definitely dimmer (and harder to see) than the rest of the screen, which looks normal. The transition in brightness is gradual – there’s not a clear “line” separating dim from normal. The image is otherwise fine – just dim in that left section of the screen. Is it a inventor problem? or backlight problem? or do I need to get a new lcd screen to fix it? Help~~~
September 20th, 2009 at 9:55 pm
Stefan,
I believe desktop LCDs have two backlight lamps inside ( I could be wrong).
Apparently one of the backlight lamps in your monitor is bad and has to be replaced. Cannot help you with that. I work only with laptops.
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!