Texas Instruments 990 Maintenance Manual page 47

+:-.
0
0
cCi"
~
-
Step
6
7
8
9
Symptom
No data from
terminal
No write re-
quest interrupt
No read re-
quest interrupt
No new status
interrupt
Table 5-1. Troubleshooting Procedures (Continued.)
Probable Cause Troubleshooting Procedure ·
Multiplexer, receive
Set up scoping loop to read
shift/buffer registers back a CRU character.
Address decoder, Set up scoping loop to set
write request flag Clear Write Request (CRU
output bit B).
Address decoder, Set up scoping loop to set
read request in- Clear Read Request (CRU
terrupt logic output bit C).
Address decoder, Set up scoping loop to set
new status flag Clear New Status Flag
(CRU output bit D)
~
Normal Indication If Abnormal
\0
+:-.
VI
+:-.
CRUDATAIN= Check circuit beginning 0
00
CRUDATAOUT at U33-l l through I
\0
U33, U7, U8, lJl,
.........
0
U9. Replace faulty
-
component(s).
WRQ=O Check circuit beginning
at Ul 8-9 through Ul8,
Ul7, U37, U35, Ul2,
U26.
RRQ=l Check circuit beginning
at U25-9 through U25,
Ul9, U25, U23, Ul 7.
Replace faulty
component(s).
NSFTG...,=l
Check circuit beginning
at U22-6 through U22,
U23, UIS, U39.
Replace faulty
component( s).