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. Venkat

    Hi,
    I m not that good in fixing the laptop, I do have the Dell inspiron 6000 and the screen went dark, so please could anybody help in fixing the problem
    I m able to connect to the external monitor and it is fine, but i wanted to fix the laptop screen help needed
    thanks,
    venkat

  2. Working on a Presario V3000. What would be an average resistance of a backlight? What would be the normal output of a functioning inverter?

  3. cj2600

    kapil,

    I have LCD goes black problem with my Sony Vaio FZ11S, already tested inverter it is working fine. I suspect strongly it has CCFL backlight got faulty. But here my question is, this 15.4 WXGA LCD screen has twin CCFL bulb so in case one CCFL bulb goes faulty other one should work Right? In that case I should get atleast some light on the screen?

    I don’t have a lot of experience with dual lamp screens, but it’s possible the dual inverter board works properly only when it’s loaded by two working backlight lamps, not just one lamp. Thus if one backlight lamp fails, the inverter board doesn’t get enough load and shuts off. Consequently the remaining working backlight lamp also stops working. This is my guess.
    If you absolutely sure the inverter board is good, I guess you’ll have to replace the screen.

    Is it possible that both CCFL goes faulty at same time?

    I think it’s possible but very unlikely.

  4. Hi, I have LCD goes black problem with my Sony Vaio FZ11S, already tested inverter it is working fine. I suspect strongly it has CCFL backlight got faulty. But here my question is, this 15.4 WXGA LCD screen has twin CCFL bulb so in case one CCFL bulb goes faulty other one should work Right? In that case I should get atleast some light on the screen? Is it possible that both CCFL goes faulty at same time? Please suggest how twin backlight works.

  5. boetix

    I have acer aspire 4715z with problems on the lcd, which only shows a white / light without seeming the least writing or drawing.
    approximately situated where the damage? on the lcd, the inverter or something else?
    thanks for the reply.

  6. I Have a preasrio v2000 I am having problems with the screen being solid white on the outer edges and in the middle a hazey white with white dots. I replaced the mother board thinking it was that. It still does this. any suggestions?

  7. dinobandhu

    i have a Lenovo Y510 laptop with me.
    i work fine but from we days my laptop flip is not stand in 90 degree position it totally get flat 180when i open my laptop . i have give support from backsight to keep it in 90 degre position

  8. Boy oh boy what a nightmare it can be figuring it out. My dell inspiron laptops screen went dark and I could not figure it out. Thank G-D for this article, at least I knew that the only way to know for sure is to get either a backlight or inverter so I figured I will go with an inverter first , found mine, installed it and viola, it turned out being the inverter. Now shes working like a charm. Thanks guys

  9. Hi! I just replaced a bad ccfl in my laptop. It went well. Next problem- when I turn it on with the lcd unplugged the whole screen lights up white but when i plug the lcd in and turn it on everything stays black. Is this a common symptom of a bad inverter? I don’t know if this helps but when I opened up the lcd the old ccfl was in two pieces and all black where the pieces met. The area over the inverter was getting really really hot. That makes me think that the inverter got too hot and broke the light. Any ideas on where the problem might lie?

  10. raghav

    Hi, I had ordered a new 15.4 inch screen for my Toshiba A 105. I noticed that the wired from the backlight of the new screen is of the “BIG” type … whereas the inverter itself accepts only the “SMALL” type. Do you have any suggestions on how I can replace the wires from the backlight? Thanks.

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