CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [341]
Figure 19-76 Hey! That’s 25,000 volts! Be careful!
The CRT monitor contains a wire called a high-voltage anode, covered with a suction cup. If you lift that suction cup, you will almost certainly be seriously electrocuted. The anode wire leads to the flyback transformer and produces up to 25,000 volts. Don’t worry about what they do; just worry about what they can do to you! That charge is stored in a capacitor, which holds that charge even if the monitor is turned off. It will hold the charge even if the monitor is unplugged. That capacitor (depending on the system) can hold a charge for days, weeks, months, or even years. Knowing this, you should learn how to discharge a CRT.
Discharging a CRT There are 75,000 opinions on how to discharge a CRT properly. Although my procedure may not follow the steps outlined in someone’s official handbook on electrical code, I know this works. Read the rules, and then look at Figure 19-77.
Figure 19-77 Discharging a CRT
1. Make sure everything is unplugged.
2. If possible, let the monitor sit for a couple of hours. Most good monitors discharge themselves in two to three hours, and many new monitors discharge in just a few moments.
3. Get a heavy, well-insulated, flat-head screwdriver.
4. Get a heavy-gauge wire with alligator clips on each end.
5. Do not let yourself be grounded in any way. Wear rubber-soled shoes, and no rings or watches.
6. Wear safety goggles to protect yourself in the very rare case that the CRT implodes.
7. Remove the monitor’s case. Remember where the screw went in.
8. Attach one alligator clip to an unpainted part of the metal frame of the monitor.
9. Clip the other clip to the metal shaft of the screwdriver.
10. Slide the screwdriver blade under the suction cup. Make triple-sure that neither you nor the screwdriver is in any incidental contact with anything metal.
11. Slide the blade under until you hear a loud pop—you’ll also see a nice blue flash.
12. If anyone is in the building, they will hear the pop and come running. Tell them everything’s okay.
13. Wait about 15 minutes and repeat.
The main controls that require you to remove the monitor case to make adjustments include those for convergence, gain for each of the color guns, and sometimes the focus control. A technician with either informal or formal training in component-level repair can usually figure out which controls do what. In some cases, you can also readily spot and repair bad solder connections inside the monitor case, and thus fix a dead or dying CRT. Still, balance the cost of repairing the monitor against the cost of death or serious injury—is it worth it? Finally, before making adjustments to the display image, especially with the internal controls, give the monitor at least 15 to 30 minutes of warm-up time. This is necessary both for the components on the printed circuit boards and for the CRT itself.
Troubleshooting LCDs
With the proliferation of LCD panels in the computing world, PC techs need to have some understanding of what to do when they break. Some of the components you can fix, including replacing some of the internal components. I tend to use monitor repair shops for most LCD issues, but let’s take a look.
An LCD monitor may have bad pixels. A bad pixel is any single pixel that does not react the way it should. A pixel that never lights up is a dead pixel, a pixel that is stuck on pure white is a lit pixel, and a pixel on a certain color is a stuck pixel. You cannot repair bad pixels; the panel must be replaced. All LCD panel makers allow a certain number of bad pixels, even on a brand-new LCD monitor! You need to check the warranty for your monitor and see how many they allow before you may return the monitor.
If your LCD monitor cracks, it is not repairable and must be replaced.
If the LCD goes dark but you can still barely see the image under bright lights, you lost either the lamp or the inverter. In many cases, especially