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. cj2600

    @ dave,

    i have a compaq presario cq60 ive had just ova a year an now the screen wont show display all shows is blue square 3/4 of screen with white squares in an a 1/4 black with the same white squares bit if i connect to external display its fine any ideas please

    It would be easier if you can take a picture of your screen and upload somewhere.
    You said the external screen works fine. Did you test it thoroughly? Does external screen work absolutely normal and there is go garbled image on it at all?

  2. cj2600

    @ R,

    After running for around 20 to 30 minutes, the display goes very dim. If I then open and then close the display, it will come back on. Once the display goes out, it only lasts for about a minute.

    Does this even in CMOS / setup so does not appear to be a setting issue.

    Tested with an external monitor and works fine. Sound more like an inverter or back light issue?

    No, it’s not settings related issue.
    Sounds like either bad inverter or failing backlight lamp. You cannot tell which one is bad without testing the laptop with spare screen or inverter.
    If you have to guess, try replacing the inverter board first.

  3. I’m having video problems with a Packard Bell Argo C2. There is a faint image on the screen. I replaced the inverter and there is still faint image. I tested to see if the inverter was getting power and it was. I tried another inverter and I get the same dark image. I tried a known good backlight and that remained dark. If I connect an external monitor the image is fine. If the inverter is getting power could it still be a faulty cable from the motherboard. I also thought it could be a stuck lid switch but I have yet to find one.

  4. hi i have a compaq presario cq60 ive had just ova a year an now the screen wont show display all shows is blue square 3/4 of screen with white squares in an a 1/4 black with the same white squares bit if i connect to external display its fine any ideas please

  5. I bought a four year old Dell Latitude D830

    After running for around 20 to 30 minutes, the display goes very dim. If I then open and then close the display, it will come back on. Once the display goes out, it only lasts for about a minute.

    Does this even in CMOS / setup so does not appear to be a setting issue.

    Tested with an external monitor and works fine. Sound more like an inverter or back light issue?

  6. cole,

    My laptop screen wont display at initially, but after 30 to 45 minutes its display normal. What went wrong ? any idea?

    How about image on the external monitor. Does it appear fine as soon as the laptop is turned on?

  7. @ Kevin,

    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.

    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?

  8. @ Igor,

    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 .

    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?

  9. 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

  10. 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

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