Datasheet

Display Devices 55
The creation of the image is known as a raster. Rasterizing an image, thus, is creating
the image in such a way that it can be displayed in a rectangular ray.
Display System Problems
There are two types of video problems: no video and bad video. No video means no image
appears on the screen when the computer is powered up. Bad video means the quality is
substandard for the type of display system being used.
No Video
Any number of things can cause a blank screen. These three are the most common: the
power is off, the monitor’s cable is unplugged, or the contrast or brightness is turned down.
If you’ve checked the power as well as the brightness and contrast settings, then the
problem could be a bad video card or a bad monitor. Most monitors these days display a
Working message briefly when you turn them on, so you can ascertain that the monitor is
working and that an amber light appears on the front. When the PC starts up, the light on
the front of the monitor changes from amber to green, indicating that the monitor is receiv-
ing a signal.
If the monitor is working but not receiving a signal from the PC, the video card may be
bad. However, no video can also mean a problem with the motherboard, RAM, or CPU, so
it isn’t a given that the video card is at fault when no video appears.
Malfunctioning monitors are usually not worth fixing, because the cost of the labor
involved exceeds the cost of a brand-new monitor. In addition, it may be difficult to find a
technician to work on a monitor, because it isn’t part of most standard PC technician training
programs (due to the risk of electric shock from the high-voltage capacitor inside the monitor).
Bad Video
A monitor that doesn’t display one of the three basic colors (red, green, or blue) probably
has a bad cable, a bent or broken pin, or a loose connection at either the PC or the monitor.
This is the case because different pins on the connectors—and wires in the cable—control
different colors.
Color problems may also result from the monitor being out of adjustment. With most
new monitors, this is an easy problem to fix. Old monitors had to be partially disassem-
bled to change these settings; new monitors have push-button control panels for changing
these settings.
Exposure to a magnetic field can cause swirls and fuzziness even in high-quality monitors.
The earth generates magnetic fields, as do unshielded speakers and power surges. Most moni-
tors have metal shields that can protect against magnetic fields. But eventually these shields
can become polluted by taking on the same magnetic field as the earth, so they become useless.
To solve this problem, these monitors have a built-in feature known as Degauss; it removes the
effects of the magnetic field by creating a stronger magnetic field with opposite polarity that
gradually fades to a field of zero. A special Degauss button or feature in the monitor’s onscreen
software activates it. You need only press it when the picture starts to deteriorate. The image
will shake momentarily during the Degauss cycle and then return to normal.
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