Troubleshooting LCDs
LCDs have far fewer user-adjustable parts than CRT displays. There is no electron gun or grids to adjust via software or hardware.
Because of this relative simplicity, troubleshooting an LCD is limited to verifying that it is correctly connected to a known-good video source, making adjustments using physical and software controls as described on the previous pages, and following the techniques discussed in this section.
Color Calibration
Customers may complain that their display's colors are “off”—not realistic, not what they expected, not matching a printed output, and so on. The colors you perceive on a display are affected by many factors, including ambient light, wall colors, the position and angle of the display, and the age of the display.
NOTE
The people who most often notice color inaccuracy are those who output color documents for print. The gamut of colors available in the electronic (RGB) and printed (CMYK) arenas varies greatly. These users must calibrate their monitors regularly, and understand and employ other techniques for color management.
Mac OS X relies on the Apple ColorSync color management system to produce accurate, predictable color from a wide variety of displays, scanners, printers, proofing systems, and presses, all of which represent color differently.
From a technical standpoint, ColorSync is fairly complex, but from a user's standpoint, it's pretty simple. You need only select color-calibrated profiles for each device and let ColorSync handle the tricky part. If you work with web or print publications, you are strongly urged to review the Help material on ColorSync.
To make color adjustments:
1. | |
2. | Click Calibrate to launch the Display Calibrator Assistant application, which takes you through the necessary steps for creating a ColorSync profile for the display.  |
3. | |
4. | If you are satisfied with the new profile, continue to use it. If not, you can return the preference to its original setting by selecting the computer's original display profile in the Color pane of Displays preferences. |
Brightness Uniformity
Brightness uniformity symptoms usually include lighter shades on the outer edges of the panel and darker shades in the center of the screen. The symptoms are most severe when the backlight bulbs have not warmed up to their optimal operating temperature. Let the display warm up (the time required to warm up varies by display and environment), and then check again for the symptoms. If the brightness uniformity doesn't improve after warm-up, consider replacing the display.
MORE INFO
Refer to Knowledge Base document 25242, “LCD Panels: Backlight Requires a Warm-Up Period.”
Pixel Anomalies
Active-matrix LCD technology uses rows and columns of addressable locations (pixels) that render text and images on screen. Each pixel location has three separate subpixels (red, green, and blue) so the image can be rendered in full color. Each subpixel has a corresponding transistor responsible for turning the subpixel on or off.
There are typically millions of subpixels on an LCD display. Modern manufacturing processes do not yet consistently yield displays in which every pixel and subpixel works perfectly. It is normal for a given LCD to have some number of pixel anomalies and be within the range of normal operation. Depending on the nature of an imperfection, it may appear only on a completely red, green, or blue image, and even then may be just barely perceptible. But displays are inspected when they are made, and units with too many imperfect pixels are not shipped to customers.
Generally speaking, technicians cannot repair pixel anomalies, but you can identify them. If a customer complains of pixel anomalies, determine the exact number of anomalies by following these steps:
1. | Use Apple LCD Tester (discussed in Lesson 2, “Software Tools”) to display a solid color image, and then check carefully when displaying solid white, red, green, and blue (different types of anomalies become most obvious under different conditions). |
2. | Using a jeweler's loupe, pocket microscope, or other magnifying device, identify and count each subpixel anomaly:
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If you or one of your customers runs across an in-warranty LCD that you feel has too many pixel anomalies, take the LCD to an Apple Authorized Service Provider (AASP) or Apple Store, and a certified service technician can confirm whether the LCD is operating within the normal range.
MORE INFO
Refer to Knowledge Base document 22194, “LCD Displays: About Pixel Anomalies.”
Don't Rub the Screen!
If a customer tells you he or she has a scratched screen, you might want to dig a little deeper to see what happened, because you might be able to prevent a “next time.” Some people believe that you can restore defective LCD pixels by rubbing the screen around the defective pixel. This procedure does not work and is very likely to create further problems (like scratched screens). Or worse, rubbing the screen can crush some of the tiny spacers that keep several of the LCD layers apart, causing even more pixel anomalies to appear.