How to Test a Laptop CCFL

Written by shoaib khan
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How to Test a Laptop CCFL
Troubleshoot your laptop's CCFL by checking its motherboard, lid switch and inverter. (laptop image by Jorge Figueiredo from

The CCFL (cold cathode fluorescent lamp) is a long, thin lamp that lights up the laptop's LCD screen. Also known as the CCFL backlight, or simply backlight, the CCFL is part of a laptop's display assembly. In producing images onscreen, the backlight lamp draws power from the inverter board, another component of the display assembly, and lights up the screen. The light is then uniformly distributed over the panel using multiple layers of thin film. Symptoms of a bad or malfunctioning CCFL include extreme dimness, flickering, a low buzzing noise from the screen, or a coloured tinge on a portion of the screen. In testing your laptop's CCFL, you should start by checking the most common and obvious reasons for malfunction, and proceed after resolving each known issue.

Skill level:

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Things you need

  • External display unit
  • Screwdriver
  • Replacement inverter board

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  1. 1

    Connect an external display with the laptop, such as a TV, monitor or projector. Plug in the unit's VGA cable to the VGA port in the laptop. You may have to switch between display modes; refer to your documentation for more information. In many laptops, you can switch between display modes by using a key combination, usually involving the "Fn" key and one of the "F" keys, marked "F1" through "F12".

  2. 2

    Check display. When you connect the laptop and switch its display mode, the external display should show your laptop's screen. If it does not, or has the same display issue as your laptop's LCD monitor, the problem is with your laptop's video card and not a part of its display assembly, such as the CCFL. If the external display produces images normally, proceed to Step 3.

  3. 3

    Check the lid switch on the laptop. This switch controls display by sending signals to the display assembly to shut down the screen when the laptop's lid is closed. The switch is usually located near the scree hinges. Make sure the switch is not stuck at "closed" position, because this will cause the LCD screen to remain blank at all times. Pry the switch loose with a pointy tool. If the switch is not in a "close" position, and the laptop still has the same display problems, proceed to Step 4.

  4. 4

    Turn off the laptop and remove the screen bezel. Undo rubber tabs and screws along the length of the bezel to detach it from the screen. Loosen the frame by pulling it out, making sure there are no locking mechanisms, such as clips or latches, still activated. With the screen bezel off, you will see the LCD panel held in place to the laptop's lid, enclosed in a metal bracket.

  5. 5

    Check the power source of the laptop's CCFL---the inverter board. This component is usually attached to a side or base of the LCD panel, and is connected to the backlight lamp with a thin cable. Detach the cable connected to the backlight by pulling it out from the inverter. Remove the inverter by undoing its screw, and hook up the CCFL backlight with a replacement inverter. Switch on the laptop and check display. If the screen still has the same problem (with a working inverter), it means your laptop's backlight is damaged and will have to be replaced.

Tips and warnings

  • Do not attempt to install a new backlight unless you are sure about the process. You will have to dismount the LCD panel and remove the lamp from its housing. This is a very involved process, and you may damage sensitive components such as the LCD panel.

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