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Table 4-2.
Digital Circuits, Symptom Troubleshooting Chart (Continued)
Symptom
2. Character disappears as
soon as key is released.
c.
d.
a.
b.
Check Procedure
Check that signal level at cor-
responding te rminals of A 13
changes 'when FRAME RESET,
CR, cursor left, cursor right,
ERASE LINE, ERASE MSG,
INSERT, DEL, ADV LINE,
BACK LINE or XMIT keys are
pre ssed.
If
the cycle function is inop-
erative, check for ab-Hz
pulse at A 13-terminal 32 when
the CYCLE and right key are
depressed.
Connect the oscilloscope probe
to terminal 3 of A13.
Press
and hold the FRAME RESET
key.
Observe on the oscillo-
scope that the frame reset
pulse is present once every
14.8 ms (once/frame).
Press and hold the FRAME
RESET key and observe the
frame pulse once/frame at
terminal 6 of A 13.
Corrective Action
If
the signal is absent,
I
replace A 14.
If present,
replace A 13.
If
the pulses are not
present, replace A 13.
If
present, perform
check b.
If
the pulses are absent,
adjust the delay line.
If
they are still absent, re-
place the A 10 board
if
the
unit has a single delay
line.
If the unit has a
L _ _ ._
---
..
- - - - -
..
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I
'
double dela y line,
p~
rform
check
£:
If the pulses are
present, replace the A 13
board.
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