How to test screen inverter

posted in: Screen, Troubleshooting | 253

In this post I explain how I test the inverter board in a laptop.

The inverter failure is very similar to the backlight lamp failure. In both cases the screen gets very dark and the image becomes very faint, barely visible under a bright light.

There is only one reliable way to test the inverter – replacing it with another one and see if the screen lights up after that.

Alternatively, you can connect a new backlight lamp and see if your presumably bad inverter lights it up.

In most cases I go with the second method – using my test backlight lamp. Why? Because the same backlight lamp will work with many different inverters as long as they have matching connectors.

Usually the inverter is mounted inside the display panel below the screen. In most cases you can access it after you remove the display bezel. The inverter has connectors on both ends. The left side connects to the LCD cable. The right side connects to the backlight lamp which is mounted inside the screen. Check out this display diagram.

To make sure that inverter gets power from the motherboard (via the LCD cable), you can test it with a voltmeter. In my case I connected the “+” lead of the voltmeter to the pin 1 and the “-” lead to the ground trace around the screw hole. I got about 19.4V DC on that side of the board, so it’s getting power from the motherboard.

WARNING! If you accidentally short something on the inverter while testing, you can damage it. Proceed on your own risk! Not sure? Don’t do that!

So far we know the inverter is getting power from the motherboard, but the screen still has no light. Apparently, it’s either bad inverter or failed backlight lamp.

Now let’s test it with a known good backlight lamp.

1. Unplug the screen backlight cable from the right side of the inverter.
2. Connect a known good backlight lamp.

Turn on the laptop.
1. If the test backlight turns on, the lamp inside the screen is bad. In this case you’ll have to replace the screen. Also, you can replace the backligth lamp which is not easy and not recommended.
2. If the test backlight doesn’t turn on, most likely we have inverter failure. Replace it and test the laptop again.

There are two different types of backlight connector, you can see them on the picture below. The top one (big) is not as common as the bottom one (small). I mostly use lamps with a small connector.

IMPORTANT! When you buy a new lamp for test, make sure the connector fits your inverter.

On the following picture you see how I’m testing the laptop with a new lamp.

Related articles:

Troubleshooting backlight failure.
Screen shows strange colors.
Troubleshooting video problems.


253 Responses

  1. Hello. My notebook Samsung R50 has its some left portion of it more darker than the rest of the LCD screen. And overall I have also noticed that my 3 year old this notebook of mine had its overall brightness reduced.
    My question is: is it the CCFL needs to be replaced or is it the inverter gone bad?

  2. faysal,

    i want to ask that this keys are not working because of new inverter?

    I don’t think so. If the screen lights up the inverter is working properly.
    I guess you are missing a piece of software controlling the Fn key.

  3. Thanks,

    No im not installing factory drivers i have to find out then istall all
    i want to ask that this keys are not working because of new invertor ? or some driver problem ok first i intalled drivers then lets see it is enable or not.

    Thanks a lot again
    Faysal

  4. sanjay dey

    Boss,
    from where i can get the company service manuals and repairing guide with flow chart for laptops of all brands, pls help me

  5. faysal,

    I’m not sure why the Fn key doesn’t work. Did you reinstall all factory drivers and software after installing XP? You can install it from the CD or download from Dell website.

  6. Hi i am facing a problem i installed new invertor in my dell laptop decause of old one is not working but my display keys function i,e Fn + Arrow keys not working i also fomate my hard disk with new partition installed Windows Xp.
    Pease help me how i can enable Fn keys funtions.

    Quick response highly be appreciated.

    Thanks

  7. David Morgan

    Just to say abig thank you for putting this up, I thought it was excellent and it has helped me in resolving the issue of the backlight I have with my Toshiba Equium Laptop.

    Props to you.

    Dave

  8. antoine,

    Most likely the pinkish screen is related to the backlight lamp failure, not the inverter failure.

  9. Great site!
    I have a related problem with my 5 year old dell latitude d810. The screen is now dark and the image on the screen is barely visible but still working. Everything else works fine. Shortly before this problem, the screen started to flash when I opened windows or was slightly pink. Your site (and others) seems to indicate that this may be the inverter or the back light of the lcd. I have looked at your other post on the backlight, but does the way the problem occurred tell me something informative about its cause?

  10. Great site!

    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

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