Keyboards

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The keyboard is the one of the most widely used peripheral input devices. It allows manual entering of characters, numbers, punctuation, and symbols that represent data and commands into a computer system. Keyboards are available in many different forms, shapes, and sizes. Most are manufactured to meet the English standard computer keyboard layout known as QWERTY. QWERTY is the first line of character keys on the top left side of the keyboard. The keyboard keys are laid out into three main groups: alphanumeric, punctuation, and special function keys. You can configure a keyboard's setting through the use of the keyboard applet in most Windows-based operating systems.

There are actually three types of keyboards: the original PC keyboard with 84 keys, the AT-style keyboard (which also has 84 keys), and the enhanced keyboard with 101 keys. The main differences between the three designs are the layout and placement of the special function keys. Today's keyboards are designed with interchangeable connectors that allow them to be used with different systems. A 6-pin mini-din (PS/2) connector is most commonly used today to connect a keyboard to a computer. (See Chapter 8 for more on keyboard connectors.)

Keyboard Technologies

There are two main keyboard technologies: switch technology, which is mechanical, and capacitive technology, which is nonmechanical. Each technology has its own specific design and usefulness.

Switch Technology

When you enter data using a keyboard, you are actually pushing on a keycap that is attached to a key switch. The key switch closes a circuit, which creates a signal. This electronic signal is converted to a digital scan code by the keyboard's processor, and is manipulated until it is finally readable by an application in American Standard Code for Information Interchange (ASCII) format.

There are two contact key switches worth mentioning:

  • Foam element and foil key switch. This key switch is a combination of stem, foam element, foil, and spring. When a key is pressed, the stem pushes on the foam, foil, and spring combination, which eventually touches copper contacts on the keyboard's circuit board to create a signal. The spring pushes the stem back up to its original position and awaits the next keystroke.

  • Rubber dome key switch. This key switch technology uses a rounded rubber dome with carbon material on its underside. When a key cap is pressed, a stem pushes on the rubber dome, which in turn pushes the carbon material onto the circuit board, thus completing the circuit.

Capacitive Technology

Capacitive technology, the nonmechanical keyboard technology, uses a switch housing that contains two conductive plates and a stem. When a key is pressed, the stem pushes the top plate toward the bottom plate, causing a change in capacitance within the switch housing. The keyboard controller recognizes the change in capacitance, and a signal is created. This technology is expensive, and with good reason: it lasts longer than switch technology and has a good level of tactile feedback.

Keyboard Troubleshooting and Maintenance

Keyboards are considered Field-Replaceable Units (FRUs). FRUs are computer parts or components that a technician can easily replace while troubleshooting computer systems in a work area or on a job site. The best way to fix a broken or defective keyboard is to replace it. Keyboards are inexpensive components. Like a computer monitor, it can cost more to have a keyboard repaired than replaced.

The keyboard is connected to a port that is connected to the motherboard. If you think you have a bad keyboard, you should verify that the problem exists with the keyboard itself and not with the motherboard. Follow these simple steps to verify if your keyboard is bad.

  1. Turn the computer off.

  2. Carefully unplug the keyboard connector from the back of the system.

  3. Plug a known working keyboard with a similar keyboard connector into the system.

  4. Turn the computer on.

If the known working keyboard is functional, the original keyboard or its connector is bad. If the known working keyboard is not functional, you most likely have a motherboard-related issue.

Keyboard problems are rare. Common keyboard issues are typically related to stuck keys or loose keyboard connectors, and are most likely detected by the POST at system boot with a 301 error (refer to POST error codes in Chapter 2).

Keeping a keyboard in good working order requires regular cleaning. To clean a keyboard, follow these basic steps.

  1. Turn the computer off.

  2. Carefully unplug the keyboard connector from the back of the system.

  3. Turn the keyboard upside down and shake it until any foreign material is dislodged.

  4. Use a can of compressed air to spray out dust and other particles.

  5. Use a very dilute combination of soap and water applied with a nonabrasive cloth to remove stains from the keycaps. Alternatively, soak the keyboard in distilled, demineralized water.

  6. Carefully plug the keyboard back into the system. (Verify that the keyboard is completely dry before doing so.)

  7. Turn the computer on.

If a keyboard has been subjected to a major soda, coffee, or other chemical spill, you can rinse it off with water or run it through the rinse cycle in a dishwasher (no-heat cycle; this is recommended only for mechanical keyboards, not capacitive). For best results, replace the keyboard.



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A+ Complete Study Guide, Third Edition (220-301 and 220-302)
The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)
ISBN: 1584503076
EAN: 2147483647
Year: 2003
Pages: 237

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