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Table 4- 2.
Digital Circuits, Symptom Troubleshooting Chart (Continued)
Symptom
7. The terminal unit is
unable to transmit or
receive data after a
message is typed into
the unit. the cursor is
re set to the be ginning,
and the EOM code
is
displayed.
8. Unable to transmit
data, receive mode is
opera tional.
a.
b.
Check Procedure
Check the voltage at A 14 pin 13
for +6 :J:2V.
Place the character select
switch on the 402-2 Test Set to
1.
Enter the ETX code in the
last character slot of the last
line.
On the test set, place the
character select switch to LAST
and connect an oscilloscope probe
to pin 14 of A 12.
Observe that
the cpA clock is 833 ±1O f.Ls.
apart.
a.
Connect the 402-2 Test Set to
J 1 of the te rmina1 unit and
enter the ETX code in the last
character slot of the last line.
Place the character select
switch on the test set to 1 and
connect an oscilloscope probe
to pin 12 of A 12.
Observe that
the level changes after" the
XMIT key is depressed.
Corrective Action
If absent, check R48 on A 14.
If pre sent, connect the 402-2
test set to J1 of the unit and
proceed to check b.
I
If incorrect, adjust R26 on
the A 14 board.
If correct
and the light readout on the
LSB
test set indicates 00000110,
the trouble is not in the
Terminal Unit.
If the level does change and
the light readout on the test set
LSB
does not indicate
0000010 I,
replace the A 14 board.
If the
level does not change, replace
the A 12 bqard.
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