Texas Instruments 990 Maintenance Manual page 46

Table 5-1. Troubleshooting Procedures (Continued)
d5-
Step Symptom
Probable Cause Troubleshooting Procedure
Normal Indication If Abnormal
'°
~
VI
Transmit shift Set up scoping loop to send
See figure 5-4. Check circuit back
~
0
ex>
clock generator
a character to terminal.
from U14-12 through
I
'°
Ul4, U6. Replace
........
0
faulty component(s).
-
Transmit bit
Set up scoping loop to send
See figure 5-5. Check circuit back
counter
a character to terminal.
from U13-12 through
U13, US. Replace
faulty component(s).
Transmit shift
Set up scoping loop to send See figure 5-6.
Check circuit back
register
a character to terminal.
from U21-8 through
U21 , Ul 1 , U20.
Replace faulty
w
'°
component( s).
5
Bad data Link driver
Actuate terminal
RCVD=O
Check circuit back
transfer from
receiver
from U41-8 through
terminal
U41 , U30. Replace
faulty component(s).
Loop back logic
Set up scoping loop to
RCVEN=l
Check circuit back
read back a CRU character
from U35-11 through
U35, U39, U20.
Replace faulty
component( s).
0
~:
Receive shift
Set up scoping loop to
See figure 5-7. Check signals in
-
~
clock generator
read back a CRU character
figure 5-7. Replace
(/)
faulty component(s).
~
-
< D
3
Receive bit
Set up scoping loop to
See figure 5-8.
Check signals in
en
0
counter
read back a CRU character.
figure 5-8. Replace
<·
faulty component(s).
c;;·
o·
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