upgrading and repairing PCs technicians ... - 400 Bad Request

228
Chapter 9—Keyboards, Mice, and Input Devices
Use Table 9.9 to help you troubleshoot a defective keyboard.
Table 9.9 Keyboard Troubleshooting
Problem Symptoms Solution
Defective cable No keyboard operation; Swap keyboard with known,
all keys produce errors working spare. If problem isn’t
or wrong characters. repeated, original keyboard is the
problem.
Replace cable with spare (if available,
check “scrap” keyboards or
vendor spare parts lists) or replace
keyboard.
Test cable with Digital Multimeter
(DMM) with continuity tester; each
wire (see pinouts previously) should
make a connection, even when you
wiggle the cable. Replace failed
cable.
Stuck key “Stuck key error” or 3xx Look up scancode from table in this
error onscreen during chapter to determine which key is
POST. stuck. Clean keyswitch.
Damaged Known-working key- For a simple test of the motherboard
motherboard boards don’t work keyboard connector, you can check
keyboard when plugged in. voltages on some of the pins.
connector 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
9.10.
Repair or replace motherboard if
voltage fails specifications.
USB Keyboard USB Legacy mode not Connect standard keyboard, start
works in enabled in BIOS/CMOS computer, start BIOS/CMOS config-
Windows 98, configuration. uration, enable USB Legacy mode,
2000, or Me, save changes, and shut down combut
not in
MS-DOS or at
startup
puter.
Reconnect USB keyboard and retry;
keyboard should now function at all
times.