Portable
PLUS
Computer
Troubleshooting
8·27
Table
8·8.
Repairing the Display (Continued)
Step
4.
Measure the voltages at the LCD connectors
A2J9
and
A2J10 on the
motherboard
PCA:
Pin
8:
0 Vdc (GND).
Pin 10:
-7
to
-13
Vdc (VLCD).
Pin
7:
4.9 to 5.1 Vdc (VccS).
5. Using a scope, check for proper
output
sig-
nals at
A2U10:
Pins 16, 18-20: toggling (DIl-DI4).
Pin
12:
260
Hz
(M).
Pin
3:
1.25 MHz (CL2).
Pin
15: 5.2 kHz (CLl).
Pin 13: 52
Hz
(FLM).
1
6.
Adjust the contrast by pressing
(Shift
)@
to
see if the display becomes visible.
7.
Take action based
upon
the observed be-
havior of the display.
8.
Using a scope, check for a toggling signal
on
these LCD controller lines: A2UlO pins
41-47
and
1-8.
Response
If
all voltages are proper, go to step 5.
If
any
voltage is
out
of range, check connections
and
traces; check the power supply according to
table 8-6,
"Repairing the Power Supply.'
If
each signal is correct, go to step 6.
If
any
signal is incorrect, check
path
through the
display cable; replace the LCD module assembly.
If
the display can be seen with
poor
contrast,
check the LCD negative power supply according
to table 8-6,
"Repairing the Power Supply
.·
If
the display
doesn't
turn
on, replace A2U10.
If
the display pixels are observed, (most easily
at
high contrast)
but
the display is blank, replace
A2U10.
If only two horizontal black stripes are present,
replace
A2U10.
If a repetitive
pattern
is displayed over the
en-
tire screen, press the reset
button
on
the
motherboard PCA (several times,
if
necessary);
check for a
bad
cable connection.
If
a
random
pattern
is displayed, go to step
8.
If
all lines toggle,
swap
the
motherboard
PCA.
If
any
address line never toggles, replace
A2UIO; exchange the
motherboard
PCA.
For further component-level troubleshooting, re-
fer to the LCD oscilloscope routines (section
8.3).
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