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How to Troubleshoot, Dissemble, and Repair a Laptop Display MoniServ, Inc.

You turn on your laptop, and nothing - just a black display. Well, the first thing you need to determine is - is it a display problem or is the system dead? Do you hear the hard drive spinning or the cooling fan blowing? If there are no signs of life, you can't expect a dead computer to display anything. If you see physical cracks in the LCD screen, it's pretty obvious that your going to need to replace the LCD.

If, when you started the laptop you heard the the hard drive spinning up, and maybe you saw the manufacturer's splash screen or BIOS startup information being displayed on the screen before it went dark, then you probably have an operating system problem. If everything is totally dark and silent, you probably have a power problem.

Another thing to suspect before taking the laptop apart is a defective operating system power saver mode. If the laptop starts normally but after a few seconds the display goes dark, it may be going into power saving mode. Certain power saving modes can cause the laptop to go to sleep abnormally and be unable to wake up. Power saving modes such as "hibernation" were especially common with older Windows operating systems. The solution is to disable all power saving modes before the system goes to sleep.

It's important to realize that almost all laptops have a connector that supports a second external display. Some laptops can be configured to disable the built-in display and use only the external display. One important troubleshooting method is to connect an external display. If you can get video on the external display, then you can eliminate the power, the operating system, and the laptops video circuitry as being the problem.

Older systems used a tiny switch to turn off the built-in display when the lid was closed. If you can see a tiny switch sticking up, you can put your finger on it and the screen would go black and it will send the video to the external port. It's common for these tiny switches to break, and not having an external monitor connected, you would assume that your computer was dead. Newer systems use a magnetic switch, so it's much less common for this to be a problem.

Many laptops use function keys to allow you to set if want to use the external port for video or if you want to send video to both the built-in display and an external monitor. To set the which display is active, you press the [Fn] key located at the lower left of the keyboard, along with a function key. Unfortunately which function key you press is not standardized.

Many laptops use the [Fn]-[F5] combination to toggle between the laptop LCD and an external display. You can usually tell which function key to use by labels or graphics on the function keys.

Another common problem with laptop displays is backlight failure. The backlight sits behind the LCD screen, shinning through the screen allowing you to see the display. The back of the laptop lid is lined with a highly reflective surface, such as metal foil, to reflect as much of the light out through the LCD as possible. If you turn on your laptop and the screen is dark but you can barely make out something on the screen then your back light has failed.

The backlight is a fluorescent bulb. Fluorescent lights need a high AC voltage to operate. A circuit board inside the laptop called the inverter circuit takes the lower DC voltage from the laptop battery and converts it to a higher AC to voltage the fluorescent back light. It's common for these inverter circuits to fail.

Inverter circuit board

To replace the fluorescent back light or the inverter circuit board, You'll need to take apart the laptop. Some newer laptops use an LED backlight, which uses DC and is much more reliable than than the inverter fluorescent bulb setup.

If you're taking apart the laptop to check the inverter board and fluorescent bulb, first check for loose or corroded connectors inside the laptop. Many times people spill liquid or drop a laptop, and it works for a while, until the liquid corrodes a connector or normal handling causes an already loose connector to separate.

Video Display Visual Anomalies

Many times you may be troubleshooting a display that is not blank, but has some visual anomalies such as bluryness or the screen image being smaller or larger than the screen. These types of anomalies are caused by configuring a screen to a non-native resolution.

All screens are manufactured with a native resolution. The native resolution of a display is the number of pixels it's designed to display in each dimension (quoted as width × height). For example, "1024x768" means the width is 1024 pixels and the height is 768 pixels.

Determine the native resolution of the laptop's LCD screen. Video drivers can usually be configured to a range of resolutions, but the resolution that will display the screen with the proper size and most crisp view is the native resolution. Check the video configuration in the operating system and make sure it's set to the native resolution of the LCD.

Standard Screen Resolutions
TypeNameResolution
VGAVideo Graphics Array640 x 480
SVGASuper Video Graphics Array800 x 600
XGA eXtended Graphics Array1024 x 768
SXGASuper eXtended Graphics Array1400 x 1050
UXGAUltra eXtended Graphics Array1600 x 1200
WUXGAWidescreen Ultra eXtended Graphics Array1920 x 1200

A permanent black line bar horizontally or vertically across the screen usually means that a cable inside the laptop has an open conductor or that a pin on a connector has lost continuity. The concept of vibrations from portability along with cheap construction can results in conductors breaking and connectors becoming lose.

Older laptops used passive matrix technology for their displays. In a passive matrix, pixels are addressed by row and column circuits. The pixel must retain its state between refreshes without the benefit of a steady electrical charge. Slow response times and poor contrast are typical of passive-matrix addressed LCDs.

Newer laptops use active matrix technology for their displays. In an active matrix, each pixel has its own dedicated thin-film transistor (TFT) transistor. Active-matrix displays have quicker response times and brighter and sharper images than passive-matrix displays.

If a visual anomoly frequently appears after a few minutes or hours of operating time, it's usually caused by an overheating problem. It may be caused by an overheating video circuit component, such as an overheating video processor or overheating video memory, or the entire laptop may be running too hot. Check for clogged vents or a cooling fan not operating.

MoniServ, Inc. is a company specializing in LCD test equipment and custom designs parts for all types of LCD screens. Established in 1989, MoniServ, Inc. has developed into a highly recognized leader in its field.


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