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Texas Instruments 990 User Manual

Texas Instruments 990
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Table 2-7. Fault Isolation Procedures When Unable
to
Load Diagnostic
~
Step
Symptom
Probable Cause
Troubleshooting Procedure
Normal Indication
If
Abnormal
\0
~
Diagnostic does not
Constant keyboard
Scope circuit.
Logic 1
at
P2-66
Trace back until fault
is
Ul
~
execute
interrupt
{Pl-66 for 2nd
located. Replace faulty
N
~
controller).
component(s).
\o
-....)
0
-
2
Diagnostic does not
Master clear not
Scope circuit.
Logic 1 at P2-66
Trace back until fault
is
load, test LED
functioning or
{Pl
-66
for 2nd
located. Replace faulty
lighted
always active
controller).
component(s).
3
Diagnostic does not
CRU interface signal
Master clear system
CRUBIT12 = 0
Remove CPU or CPU
load
shorted to another
(cycle chassis power
CRUBIT13 = 0
buff
er. Ground each
signal or
to
ground
off
and back on)
CRUBIT14 = 0
input. Check effect
of
CRUBIT
15
= 0
grounded input on other
CRUBITOUT = 0
input. Check continuity
STORECLOCK- = 1
to
locate short circuit
MODSELA- = 1
path. Repair.
N
I
MODSELB- = 1
N
-
CR UBITINT = 1
NKBINT = 1
4
Diagnostic does not
CRU interface signal(s)
Same
as
for step 3
Same
as
for step 3.
Remove VDT controller.
load, CRU lines
not
shorted
to
ground
Check CRUBIT, 12-15,
shorted to each
and CRUBITOUT for
other
ground.

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Texas Instruments 990 Specifications

General IconGeneral
BrandTexas Instruments
Model990
CategoryDesktop
LanguageEnglish

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