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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October 13th, 2009 at 11:02 pm
Tony,
Instead of rebooting the laptop, try tapping on the lid close switch – a small button by the hinge. Can you light up the screen when tapping on the switch?
On some IBM laptop it’s really hard to see anything on the screen when the backlight is off, so look very closely.
Your descriptions sounds like a problem with the inverter or backlight lamp. Try replacing the inverter board first, they are not expensive.
I would find the FRU part number on the existing inverter and use it for buying a new one. It’s not difficult to removed the bezel, takes only 5 minutes. You don’t have to disassemble the entire display, simply lift up the lower part of the bezel, find the inverter part number and put it back together.
October 9th, 2009 at 2:05 pm
Hi,
Great site! I have an IBM T30 and came home one day to the screen being dark. It lights up during reboot, logs on to windows and goes black again. I don’t see any faint image, but maybe I need to look harder with a flashlight. The unit has a docking station. I setup an external CRT on the docking station and it works fine. Device manager says everything is fine. The properties tab for display shows two screens inclduing the CRT and LCD. It says the LCD is “not active” if I recall right. I’m wondering if this is a problem with the inverter? The docking station probably has a card in it that is operating the CRT? Also, before ordering an inverter, I can’t determine which one it is. There are two different part numbers out there for my model and I don’t really want to take the laptop apart twice, once to find the number and one to install the part when I get my hands on one. I went to numerous sites, but they just identify with the T30 verus the full model which is a T30 236697U. The two part numbers I am finding out there are: 26P8412 (150nit LCD) and 26P8411 (200nit LCD. What are the nits? I have gone to the Lenovo / IBM site. It only lists an inverter / screen combo pack number for certain models and does not even list this model number. Thanks.
October 7th, 2009 at 7:27 pm
Hi,love this,it is so informative!
I’m having a similar problem,but not quite the same as what I’ve been reading & I hope you can help me.
I have a Dell Inspiron l6400 laptop. Nothing has happened to it, one day I turned it on & the bottom 1/3 of the screen has gone white/gray. There still seems to be light, but can’t see anything. When it 1st started,I could tap the bottom of the laptop it would come back on, but nothing brings it back now.
I took things apart to check for loose connection to lcd panel. Everything seems ok,no visible damage or anything. Checked the connection,unplugged & plugged the cable back in where it connects by the power button – nothing! Hooked it up to another monitor & dispaly on that monitor is fine.
Does that mean I need to replace the entire LCD, or could it be a bad cable or something else? I don’t want to spend a lot of $ to replace something & have it still not work!
I appreciate any advice/help you can give me.
October 7th, 2009 at 2:10 pm
I have an HP ze5478cl. the lcd works for a minute goes grey then rolls like an old tv set with vertical hold problems, then comes back. it works fine with an external monitor.
so , my question is…LCD? Inverter? backlight? which is bad?
Thanks, Ron
October 5th, 2009 at 4:37 am
hi
dear
i study y r above page really very intrested
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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.