Apple CRT Displays

Apple continues to sell the CRT-based eMac, and there are literally millions of CRT-based iMac models still in use today. Therefore, it's important to familiarize yourself with these computers and their service issues.

User Controls

Users control Apple displays through physical controls as well as Display preferences. These controls often provide different ways of adjusting the same thing, such as brightness.

Physical Controls

To access the physical controls, simply check the front panel of the display itself, or consult the display's user's manual if you can't locate the controls by sight.

Different Apple displays have different control configurations. Some have controls for power, contrast, and brightness.

Display Preferences

To access the controls through software, choose System Preferences from the Apple menu, and then click Displays.

The Displays pane in System Preferences provides features based on the type of display that is connected to the computer system. User controls accessible through software include resolution, colors, refresh rate, brightness and contrast, geometry adjustments, and color calibration (these last two are discussed in the “Troubleshooting CRT Displays” section). (Because LCDs don't suffer from geometric distortion as do CRTs, there are fewer settings in an LCD Displays pane.)

Resolution

Use the settings on the Display tab to make images appear larger or smaller (called changing the resolution). For best results, select the “Show modes recommended by display” checkbox (if available). With higher resolutions, the Mac can display more information, but text may become so small that it's hard to read for some users. Choose a resolution that suits the customer's needs.

Colors

If images on the display appear grainy, try choosing a greater number of colors from the Colors pop-up menu. For the most realistic images, you should choose the maximum number of colors available, but some applications (notably games) require a specific color setting. The number of colors a Macintosh can display at a given resolution is a function of the amount of installed video random-access memory (VRAM), which may or may not be expandable, depending on the model.

Refresh Rate

The refresh rate setting determines how often the display refreshes the image. Normally, you want to have a display refresh at least 75 times per second. This minimum rate reduces the user's chance of eyestrain. If you choose a refresh rate that's too slow, the human eye can discern the drawing of the screen as an annoying flicker. Higher refresh rates provide a more stable image. However, some high-end graphics controllers can refresh too fast for some displays. Check the display's specifications for maximum supported refresh rate before cranking up the controller.

Brightness and Contrast

Making changes to the brightness and contrast settings affects the color that appears on a display. The higher the brightness setting for your screen, the more washed out the colors may appear. For best color, set the brightness to the middle setting, and then adjust the contrast to change the overall luminance of the display.

Screen Savers

CRT-based displays can have a ghostlike image permanently burned into the phosphors of the screen if the display is left displaying a static image (such as a company logo on an older video arcade machine) for a very long time. To combat this problem in Mac OS X, choose System Preferences from the Apple menu, click Desktop & Screen Saver, click the Screen Saver tab, and select any one of the many built-in screen-saver modules. Using the slider, set the screen saver to start after a reasonable idle period.

From the standpoint of energy consumption, putting the computer to sleep or shutting it down is preferable to running a screen saver indefinitely. The Energy Saver pane in System Preferences has a setting for display sleep that works for internal and standalone displays.