Portable
PLUS
computer
Trouble.hootlng
8·21
Table 8·6. Repairing the Power Supply (Continued,
Step
VccDS
Regulator Problem:
5.
Measure VccDS: A2U17 (PPU), pin 40.
6.
Monitor the SLEEP signal with a scope
while pressing
@)
(or other keys): A2U17,
pin 34.
7.
Unsolder
and
lift the drain lead of A2Q70;
then
measure
VccS
at
the lifted drain lead.
LCD Supply Problem:
1
Response
If
VccDS is less
than
1 Vdc, check A2VR50 (pro-
duces regulated voltage of 1.23 Vdc), check
A2Q63, A2Q66,
and
A2Q62 for open circuit; re-
place the motherboard PCA.
If
VccDS
is
between 3.2
and
3.4 Vdc, go to step
6.
If
VccDS
is
between 4.0
and
4.9 Vdc, go to step
6.
If
VccDS is the same as
VBAT
(measured
at
the
battery terminals), replace A2Q63; replace the
motherboard PCA.
If
VccDS is outside
any
of
the above ranges, re-
place the motherboard PCA.
If
the SLEEP signal goes low (less
than
1
V),
go
to step
7.
If
the SLEEP signal stays high or "floats' be-
tween high and low, check the processors using
the procedure in table 8-7, "Repairing the
Processors:
If
the drain voltage is between 4.9
and
5.1 Vdc,
swap
the mempry PCA;
swap
the motherboard
PCA.
If
the drain voltage stays low, check A2Q63; re-
place the motherboard PCA.
8.
Measure LCDON signal
on
A2U17 pin 16.
If
LCDON is high, use the procedure in table 8-
7,
'Repairing the Processors:
9.
Measure the collector voltage
of
A2Q77.
If
VLCD
is
between
-7
and
-13
V dc, the
sup-
ply voltage is in the proper range.
Skip
to
step
12.
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