Portable
PLUS
Computer
Troubleshooting
8-29
Table 8-9. Repairing the Keyboard (Continued)
Step
4.
Turn
on
the
computer. (Press
CID
or
other
keys, if necessary.)
s. Using a scope, check for a 2.67-MHz signal,
50%
duty
cycle (MCLK)
at
A2U16
pin
23.
6.
Check individual keys: use a scope to moni-
tor
the
corresponding column line
(and
then
row line) at A2U16 while pressing
and
holding
the
key. (Refer to figure 12-11.)
C1
(pin 14)
Rl
(pin 22)
C2 (pin 13)
R2
(pin 21)
C3 (pin 12)
R3
(pin 20)
C4 (pin 11)
R4
(pin 19)
C5 (pin
10)
R5
(pin 18)
C6 (pin 9) R6 (pin 17)
C7
(pin
8)
R7 (pin 16)
C8 (pin 7)
R8
(pin 15)
C9 (pin 6)
CIO (pin 47)
CII
(pin 46)
C12 (pin 48)
C13
(A2UI7, pin 36)
7. Using a scope,
monitor
the
SYSINT* line
(A2UI6,
pin
34)
while
pressing
and
holding
any
key
(but
not
(ill)
.
I
Response
If
present, proceed to step
6.
If
signal is missing
or
bad, verify
that
unit is
turned
on
.
Then
trace signal back to A2U6
pin
2;
unsolder
and
disconnect
pin
at
A2U6,
then
check signal to see if A2U6 is
the
problem.
For
C10 through C13: if the signal is lower
than
1 V while the key is held
and
higher
than
4V
while the key is released,
the
key
is
good; other-
wise, replace the keyboard
module
.
For
other
lines:
if
an
l1.25-JLs-low,
l2
.0-JLs-high
square-wave signal is observed
on
both
the
row
line
and
column line,
the
key is
good
.
•
If
you can
load
and
run
the
disc-based
di-
agnostic tests, check
the
keyboard using
the
main diagnostic procedure in section 8.2.1.
•
If
you
can't
use
the
disc-based diagnostic test,
go to
step
7.
For
other
lines: if a different signal is observed
on
either the row line or column line, check
the
signals for
other
keys in
that
row
and
for
other
keys in that column.
•
If
the
signal is
bad
for only
one
key, replace
the
keyswitch (or keyboard module).
•
If
the
signal is
bad
for
an
entire
row
or col-
umn
, check continuity
between
A2U2
and
the
keyboard; replace A2U2.
If
signal periodically pulses
low
while
key is
pressed,
swap
the
motherboard
PCA.
If
signal
doesn't
pulse low
while
key is pressed,
replace A2U16.
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