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Troub ........ i .... nd DI •• noatlc. 8-33
,..... .... Dlaptar/GPU Troubleshooting IIndIl .... i'
Use the following procedure to troubleshoot and repair a display jGPU problem.
In each of these
steps, always turn off the power before
you
connect or disconnect a cable or replace a component.
Note. Do
not attempt to
repair
the display assembly itself. It is a
tuned assembly
and must
be replaced
with an
exchange assembly if it is faulty.
Early versions of the display assembly may have a small PCA installed on the back of the
assembly.
This
PCA
contains some drc:uitry that has been incorporated into the display
assembly main PCA in later units. Do not remove the small peA, if present, from a display
assembly
or
transfer it to a new display assembly.
ltep
t.
H
the entire display pattern is shifted down
and to the left, it is likely that the GPU is
running in CRT
mode. That is, the GPU is
configured for a CRT monitor rather than
for the electroluminescent
(EL)
panel· dis-
play. This is caused by a bit in the real-time
clock becoming changed from its normal
value.
2.
Set up the computer to troubleshoot the
logic B peA (refer to table 8-27). Repeat the
display test. If you get one of the following
error
messages, take the indicated action.
Otherwise go on to step 3.
***
ERROR - 201
***
ERROR - CPU
tim. out
error
***
ERROR - Display RR" (R/W)
error
I
InciloatecI Action
To
reconfigure
the GPU for normal operation,
proceed as follows:
a.
Insert the System Disc in the disc drive and
turn on the computer.
This
resets the bit in
the real-time clock, but the display is still
shifted.
b. Turn off the power.
c.
Turn on the power again. The display
should now be back in its normal
(EL)
mode.
If the error message appears, or if you hear a
descending
musical scale, a GPU failure is proba-
ble. Replace UI (the GPU) on the logic B PCA.
Check pin 33 of UI for a 3-MHz signal:
• If not present, troubleshoot the 3-MHz sys-
tem clock (table 8-23).
• If
present, replace Ul on the logic B peA.
Replace the logic B PCA.
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