CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [340]
Hissing or sparking sounds are often indicative of an insulation rupture on the flyback transformer. This sound is usually accompanied by the smell of ozone. If your monitor has these symptoms, it definitely needs a qualified technician. Having replaced a flyback transformer once myself, I can say it is not worth the hassle and potential loss of life and limb.
Big color blotches on the display are an easy and cheap repair. Find the Degauss button and use it. If your monitor doesn’t have a Degauss button, you can purchase a special tool called a degaussing coil at any electronics store.
Bird-like chirping sounds occurring at regular intervals usually indicate a problem with the monitor power supply.
Suppose you got a good deal on a used 19-inch monitor, but the display is kind of dark, even though you have the brightness turned up all the way. This points to a dying CRT. So, how about replacing the CRT? Forget it. Even if the monitor was free, it just isn’t worth it; a replacement tube runs into the hundreds of dollars. Nobody ever sold a monitor because it was too bright and too sharp. Save your money and buy a new monitor.
If the monitor displays only a single horizontal or vertical line, the problem is probably between the main circuit board and the yoke, or a blown yoke coil. This definitely requires a service call.
A single white dot on an otherwise black screen means the high-voltage flyback transformer is most likely shot. Take it into the repair shop.
External Adjustments
Monitor adjustments range from the simplest—brightness and contrast—to the more sophisticated—pincushioning and trapezoidal adjustments. The external controls provide users with the opportunity to fine-tune the monitor’s image. Many monitors have controls for changing the tint and saturation of color, although plenty of monitors put those controls inside the monitor. Better monitors enable you to square up the visible portion of the screen with the monitor housing.
Finally, most monitors have the ability to degauss themselves with the push of a button. Over time, the shadow mask picks up a weak magnetic charge that interferes with the focus of the electron beams. This magnetic field makes the image look slightly fuzzy and streaked. Most monitors have a special built-in circuit called a degaussing coil to eliminate this magnetic buildup. When the degaussing circuit is used, an alternating current is sent through a coil of wire surrounding the CRT, and this current generates an alternating magnetic field that demagnetizes the shadow mask. You activate the degaussing coil by using the Degauss button or menu selection on the monitor. Degaussing usually makes a rather nasty thunk sound and the screen goes crazy for a moment—don’t worry, that’s normal. Whenever a user calls me with a fuzzy monitor problem, I always have them degauss first.
Troubleshooting CRTs
As shipped, most monitors do not produce an image out to the limits of the screen, because of poor convergence at the outer display edges. Convergence defines how closely the three colors can meet at a single point on the display. At the point of convergence, the three colors combine to form a single white dot. With misconvergence, a noticeable halo of one or more colors appears around the outside of the white point. The farther away the colors are from the center of the screen, the more likely the chance for misconvergence. Low-end monitors are especially susceptible to this problem. Even though adjusting the convergence of a monitor is not difficult, it does require getting inside the monitor case and having a copy of the schematic, which shows the location of the variable resistors. For this reason, it is a good idea to leave this adjustment to a trained specialist.
I don’t like opening a CRT monitor. I avoid doing this for two reasons: (1) I know very little about electronic circuits, and (2) I once almost electrocuted myself. At any rate, the CompTIA A+ exams expect you to have a passing understanding of adjustments you might need to perform inside a monitor. Before