Matsushita Electric KM40108849C3, Service Manual

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2. Reception signal path:
Signals receive from the telephone line are outputted at the
speaker via the following path:Tel line Q108 Q109 C112
R600 C603 Pin 27 of IC601 Pin 26 of IC601 Pin 19 of
IC601 Pin 15 of IC601 Speaker.
3. Transmission/Reception switching
The comparison result between TX and RX outputs as a DC level
of Pin 25 of IC601.TX level is high ...... Pin 25 = Pin 21 - 6mVRX
level is high ...... Pin 25 = Pin 21 - 150mVComparator output is
connected to the attenuator control inside of IC601.
4. Voice detector
The output of the mic amp (Pin 10 of IC601) is supplied to Pin 13
of IC601 as a control signal for the voice detector.
5. Attenuator control
The attenuator control detects the setting of the volume control
through Pin 24 of IC601 to automatically adjust for changing
ambient conditions.
13.4. Telephone Line Interface
13.4.1. Circuit operation
- On hook
Q101 is open, Q101 is connected as to cut DC loop current and cut
the voice signal.
- Off hook
Q101 turns on thus providing an off-hook condition (active DC
current flow through the circuit) and the following signal flow id
for the DC loop current. T POS101 D101 Q101 Q108
R124 D106 D101 R
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