Sanyo CLA-1380 Service Manual page 39

CIRCUIT DESCRIPTION
.
a
(3) The branch detection circuit
The branch detection circuit serves to detect the signal that is emitted when a telephone that is branch-connected goes
off-hook while CIA-1 380AUS is in the auto answer mode.
The circuit then informs IC401 and stops the auto answer mode.
When the telephone line enters the closed stated (i. e. off-hook), the direct current from the telephone line flows
through telephone line @ to @.
At this time, Q901. Q902 drive IC902, then switched pin 44 in IC401 "L" and "H".
L
Branch detection condition
Detection begins 2.5 sec. following off-hook.
"L" is detected if pin 44 in IC401 if it continues for 500 msec or more.
BRANCHES(OFF-HOOK)
TEL LINE
@to@
I
o
IC401 PIN 43
II
(4) The VOX (Voice activate recording) detection circuit
This circuit determines whether the signal sent from the telephone line while CIA-1 380AUS is in the auto answer mode
is voice, a busy signal, silence or a continuous sound, then stops auto answer mode.
While in the auto answer mode, the signal from the telephone line is input to pin 3 in IC702.
After being amplified by the Amplifier inside IC702, the signal is output from pin
8
in IC702 and sent to pin 10 in IC702.
Then, the waveform shown in the figure below is output from pin 20 in IC702.
VOX detection conditions
The signal is interpreted sa a voice if "T" does not occur in 8 seconds in the following range:
15~T~8fJ msec or 900 ~T~ 3r)orJmsec.
VOICE
IC702
PIN 10
1
[
I
I
I I
IC702
PIN 20
(IC401 PIN 47)
T
* >
IC702
="
'
'
LINE AMPLIFIER
>
T901 Q701
j—~ iC401 PIN 47 (VOX)
&f
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