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4-1.9 Digital Circuits
Table 4- 2. Digital Circuits, Symptom Troubleshooting Chart
Symptom
1.
Unable to write a char-
acter or characters or
perform functions such
as carriage return, cur-
sor left, etc., when
proper keys are pressed.
Check Procedure
Note:
Cheek the voltages at the
terminals of the digital cir-
cuits (use fig. 4-3 fcir iden-
tification of terminals that
handle the de voltages on the
circuit boards).
a.
Press and hold the keys.to
paint the characters listed and
check that the signal level
changes occur at the terminals
on board A13 as listed:
-
FXO FXI FX2 FYO FyI FY2
Key
on
on
on
on
on
on
41
53
60
55
58
56
v
o
1
1
0
.1
I
M
1
o
1
1 -',0
1
D
o
o
1
0
0
1
9
1
o
o
1
1
a
b.
Check that strobe level at
Corrective Action
If
functions or characters do
not check out
in~.
b, or
£.
replace keyboard assembly
All.
If
present, replace
A
13.
L
A13-27 changes when'any char-
acter key is pressed.
. --------L-----~---L--. _ _ _
_ _ _ J
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