Texas Instruments 990 - Page 130

N
N
00
Step
Symptom
Alarm duration out
of tolerance
Table 2-11. Fault Isolation Procedure for Apparent Alarm Problems
Probable Cause
Defective alarm
logic (figure 148)
Built-in test
logic (figure 1-33)
Troubleshooting Procedure
Execute part 4
(E4) alarm test.
Loop on part l
(LI).
Normal Indication
See figure 2-8.
.28 - .32 sec at 50 Hz
.23 - .27 sec at 60 Hz_
BBTSL follows AQ.
If Abnormal
Trace circuit back from
U79-6 (U3 7-6 for 2nd
controller). Replace
faulty component(s).
Sync on AQ at U79-6
(U37-·6 for 2nd contro:l-
ler). Trace foirward from
U80-9 (Ul 8-9 for 2nd
controller). Replace
faulty component(s).