Hardware Reference
In-Depth Information
with the continuity in one of the wires, replace the cable or the entire keyboard, whichever is
cheaper. Because replacement keyboards are so inexpensive, it's almost always cheaper to replace
the entire unit than to get a new cable, unless the keyboard is an expensive unit like an older IBM
Model M. You can get replacement cables (and other parts) for older IBM Model M type keyboards
from
www.clickykeyboards.com
.
Testing, and Maintenance
.”
Many times you first discover a problem with a keyboard because the system has an error during the
POST. Many systems use error codes in a 3xx numeric format to distinguish the keyboard. If you
encounter any such errors during the POST, write them down. Some BIOS versions do not use cryptic
numeric error codes; they simply state something such as the following:
Keyboard stuck key failure
This message is usually displayed by a system with a Phoenix BIOS if a key is stuck. Unfortunately,
the message does not identify which key it is!
For a simple test of the motherboard keyboard connector, you can check voltages on some of the pins.
Using
Figure 15.8
(shown earlier in the chapter) as a guide, measure the voltages on various pins of
the keyboard connector. To prevent possible damage to the system or keyboard, turn off the power
before disconnecting the keyboard. Then unplug the keyboard and turn the power back on. Make
measurements between the ground pin and the other pins according to
Table 15.2
,
shown earlier in the
chapter. If the voltages are within these specifications, the motherboard keyboard circuitry is
probably okay.
If your measurements do not match these voltages, the motherboard might be defective. Otherwise, the
keyboard cable or keyboard might be defective. If you suspect that the keyboard or cable is the
problem, the easiest thing to do is to connect a known-good keyboard as a test. If the system works
properly with the known-good keyboard, you know the original keyboard or cable is defective. If the
system still does not work normally, you might have to replace the motherboard.
Cleaning a Keyboard
One of the best ways to keep a keyboard in top condition is periodic cleaning. As preventive
maintenance, you should vacuum the keyboard weekly, or at least monthly. When vacuuming, you
should use a soft brush attachment to dislodge the dust. Also note that some keyboards have keycaps
that come off easily, so be careful when vacuuming; otherwise you may have to dig the keys out of the
vacuum cleaner. I recommend using a small, handheld vacuum cleaner made for cleaning computers
and sewing machines; these have enough suction to get the job done with little risk of removing your
keytops.
You also can use compressed air to blow the dust and dirt out instead of using a vacuum. Before you
dust a keyboard with the compressed air, however, turn the keyboard upside down so that the
particles of dirt and dust collected inside can fall out.
On most keyboards, each keycap is independently removable, which can be handy if a key sticks or
acts erratically. For example, a common problem is a key that does not work every time you press it.
This problem usually results from dirt collecting under the key. An excellent tool for removing
keycaps on almost any keyboard is the U-shaped chip puller included in many computer tool kits.
Simply slip the hooked ends of the tool under the keycap, squeeze the ends together to grip the
