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.

A generic display assembly includes a very few parts and knowing them will help you to understand witch part can cause a problem if you laptop video not working properly.

Video cable. A video signal from the motherboard goes to the LCD screen through the video cable. The video cable connects to the motherboard (or video card) through the connector 1. The video cable connects to the LCD screen through the connector 2. The video cable (in most cases) is also responsible for supplying a necessary voltage for the FL inverter board. The video cable connects to the FL inverter board at the point 3.

FL inverter board. This board is responsible for converting low voltage DC power (point 3) to high voltage AC (point 4), necessary to light up the backlight bulb. If the FL inverter board is bad, the LCD screen (backlight bulb) will not light up when you turn on the laptop, but you still should be able to see a very dim image on the screen.

Looking for a new screen, video cable or inverter board? Find it here.

CCFL (backlight bulb). When the backlight bulb lights up, you can see an images on the LCD screen. In most cases the backlight bulb is a part of the LCD screen and if it’s bad, the entire screen has to be replaced. By the way, some specialized repair shops can replace the backlight bulb itself.

Lid close switch. The lid close switch is a small button that locates close to the display hinges. On some newer models there is no button, because the switch is magnetic. You can set up your laptop to go to a hibernation mode or to a standby mode when the LCD is closed. It’s done through power management software. These modes are triggered when the display is closed and the lid close switch is pressed down. If the LCD screen on your laptop will not light up when you open the display assembly, check the lid close switch is stuck inside (it might happen because the switch is dirty).

Related articles:

Fixing notebook video problems.

Disassemble LCD screen with water damage

Screen inverter replacement.

Laptop has bad video on the screen.

Here’s another helpful laptop buying guide.

From myself I would like to add some hardware related details you should think of before you buy a notebook computer.

Laptop AC Adapter.

Make sure to check the size of the AC adapter before you buy a laptop. Usually, you do not see the AC adapter before you buy the laptop and open the box at home. You’ll be very surprised to see that your AC adapter is half-size of your computer. I did this mistake when I bought Sony Vaio PCG-FRV26. The AC adapter wasn’t designed for a portable computer at all.

Volume Control.

If you like listen music a lot then you have to choose a laptop with some kind of a hardware sound volume control (sound volume buttons or sound volume wheel located on the laptop). I prefer a volume wheel like on most Toshiba laptops. The volume wheel gives you almost instant access to the sound level. If you do not have a hardware control, then the only way to change the sound volume is through the software settings; it takes some time.

Sound System.

This is again for music lovers. Make sure to find a laptop with a good sound system. In my opinion, Harman/Kardon system is one of the best. I have Harman/Kardon speakers on my HP Pavilion zv5430us and the sound is awesome. Sound on my Sony Vaio laptop sucks!

Laptop Memory Location.

The system board is one of the most important and most expensive parts of a notebook computer and you will get an advantage if you know what kind of the system board installed into the laptop. Some modern notebooks have memory integrated on the system board and offer only one extra memory slot to expand the memory size in the future. If onboard memory goes bad, you have to replace the entire system board. It’s OK if your laptop is still under warranty, but what if you have to pay cash for the repair? Also you cannot upgrade onboard memory. Other type of system boards do not have onboard memory, instead offer to you two memory slots on the system board. You will have to replace only the memory stick if it goes bad. System board with 2 memory slots usually can accept up to 2 GB of memory (1GB memory stick in each slot). So, if you plat to upgrade your laptop in the future, make sure that your laptop has both memory slots available for upgrade. Ask a sales person for details.

USB Port Location.

Check how USB ports are located on the laptop. If you plan to use USB devices like a wireless mouse, a flash drive or an external USB hard drive, then it would be nice to have couple USB ports on the side of your laptop not only on the back. Some laptops do not have USB ports on sides and to connect an USB device you have to turn the laptop.

Make sure that USB ports are not located too close to each other. Some older USB devices are big and when you plug it into one USB port, the second USB port becomes unusable.

Keyboard.

If you are a network administrator or have a job related to networking, then probably you use Windows run box a lot. To access the run box in Windows you use a shortcut (Windowd Key + R button). On some keyboards the Windows Key is located in the lower left corner, so you can use one hand to start it. On some keyboards the Windows Key is located in the upper right corner and to start the run box you have to use both hands. Choose the right keyboard for you. For some people it’s not a problem at all, but what if you use this shortcut hundreds times a day?

Parallel Port.

Very often this option is overlooked. If you plan to connect a printer to your laptop via a parallel port then you have to find a laptop with this option. Many modern laptops are designed for modern USB printers and they do not have the parallel port at all.

Laptop Warranty.

If you think that notebook computers do not fail or they fail only during the first year of exploitation, think again. In my opinion, an extended 3or 4 years warranty is a must for any notebook computer. For example I’ll give you approximate prices for some Toshiba Satellite A75 laptop parts if you decide to repair it in Toshiba Repair Center.

System board – from $400

LCD screen – from $550

Pentium CPU – from$300

CPU cooling fan – from $80

Keyboard- from $70

Do not forget to add labor charges -“ from $60/hour

Laptop hardware is very specific and you cannot just buy it in any computer store. I am a laptop repair technician and I have 2 laptops at home. I bought an extended warranty for both my computers.

I would prefer to buy $800 laptop and pay $300 for extra 3 years warranty than to buy $1100 laptop with a standard 1 year warranty. Think about it.