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Int ............... COIIqtUter
,...... .... Dlapl-w/GPU Trou ..... booti •• and R . . . . (ConIIMIed)
Step
S.
Check the 6-MHz video clock signal at pin
11
of
U13
on the logic B PCA.
.. Run the display test on the service ROM
and stop at a checkerboard pattern. While
the checkerboard pattern is on the display,
check the
VSYNC
signal at pin 45 of Ul
(the GPU) on the logic 8 PCA.
7. While the checkerboard pattern is still on
the display, check the
HSYNC
signal at pin
5 of UI0 on the logic 8 PCA.
Ind ...... ActIon
If the signal is not present, check for the clock
signal at pin 13 of U13.
• If the signal
is
present at pin 13, but not at
pin 11, replace U13 on the logic 8 PCA.
• If the signal
is
not present at pin 13 of U13,
troubleshoot the 6-MHz system clock (refer to
table 8-23) .
The waveform should be as follows:
., .. - t.. ..., ... -.
.
.
.L
•
H
the waveform is not present, replace
UI
on
the logic 8 PCA.
The waveform should be as follows:
_, .. -t.. . . . , .. -
ao
.
•
If
HSYNC
is not present at pin 5, check for
HSYNC at pin 12 of UIO on the logic B PCA.
• If
HSYNC
is present at pin 12. but not at pin
5, replace UIO on the logic B PCA.
• If
HSYNC
is not present at pin 12 of
UIO,
check for a signal at pin 46 of U 1 on the logic
8 PCA. If not present, replace U
1.
If present,
replace the logic B PCA.
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