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A+ Exam Cram: Hardware Troubleshooting Techniques

Nov 5, 2004

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A+ Certification Exam Cram 2 PC Maintenance and Troubleshooting Field Guide

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Troubleshooting Keyboard Problems

Most of the circuitry associated with the computer's keyboard is located on the keyboard itself. However, the keyboard interface circuitry is located on the system board. Therefore, the steps required to isolate keyboard problems are usually confined to the keyboard, its connecting cable, and the system board.

Keyboard Symptoms

Typical symptoms associated with keyboard failures include the following:

No characters appear onscreen when entered from the keyboard.
Some keys work, whereas others do not work.
A Keyboard Error—Keyboard Test Failure error appears.
A KB/Interface Error—Keyboard Test Failure error appears.
An error code of six short beeps is produced during bootup (BIOS dependent).
The wrong characters are displayed.
An IBM-compatible 301 error code appears.
An Unplugged Keyboard error appears.
A key is stuck.

Basic Keyboard Checks

The keys of the keyboard can wear out over time. This might result in keys that don't make good contact (no character is produced when the key is pressed) or that remain in contact (stick) even when pressure is removed. The stuck key produces an error message when the system detects it; however, it has no way of detecting an open key.

An unplugged keyboard, or one with a bad signal cable, also produces a keyboard error message during startup. Ironically, this condition might produce a configuration error message that says "Press F1 to continue."

If the keyboard produces odd characters on the display, check the Windows keyboard settings in Device Manager. Device Manager is located under the System icon (found in Control Panel) in Windows 9x and Windows Me. In Windows 2000, the path is similar—Control Panel, System, Hardware tab. However, in both Windows 2000 and Windows XP, Device Manager is usually accessed through the Computer Management console. If the keyboard is not installed or is incorrect, install the correct keyboard type. Also, be certain that you have the correct language setting specified in the Keyboard Properties dialog box (found by double-clicking the Keyboard icon in Control Panel).

Keyboard Hardware Checks

If you suspect a keyboard hardware problem, isolate the keyboard as the definite source of the problem (a fairly easy task). Because the keyboard is external to the system unit, detachable, and inexpensive, simply exchange it with a known-good keyboard.

If the new keyboard works correctly, remove the back cover from the faulty keyboard and check for the presence of a fuse in the +5V DC supply and check it for continuity. Neither the older five-pin DIN nor the six-pin PS/2 mini-DIN keyboards can be hot-swapped. Disconnecting or plugging in a keyboard that has this type of fuse while power is on can cause the keyboard to fail. If the fuse is present, simply replace it with a fuse of the same type and rating.

If replacing the keyboard does not correct the problem, and no configuration or software reason is apparent, the next step is to troubleshoot the keyboard receiver section of the system board. On most system boards, this ultimately involves replacing the system board.

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