Panasonic KX-FT25LA, Service Manual

Page: 135 / 167

6.8.5. LINE AMPLIFIER AND SIDE TONE CIRCUITS
1. Circuit Operation
The reception signal received as output from line transformer T1 is given as input to C14, R13 and IC2(2).
Then it is input to the reception system at an amplifier gain of 3.3 dB from pin (2).
The transmission signal is input from CN1 pin (11), and output to the TEL line through C6, R14 and T1. Without a side tone
circuit, the transmission signal would return to the reception amplifier via C6 and R14. Here, the signal output from CN1 pin (11)
passes through C6, C36 and R12, and enters the amplifier IC2 pin (3). This is used to cancel the return portion of the
transmission signal. This is the side tone circuit.
6.8.6. CPC (Calling Party Control) DETECTION CIRCUIT
1. Function
This circuit detects the signal (cuts the current) output from the converter when the other party finishes ICM recording
and goes into the ON-HOOK status.
TAD detects this signal and disconnects the line. When the TAD is operating, pin (4) of PC2 becomes a low level.
While detecting the CPC signal, pin (4) of PC2 becomes a high level. When the CPC signal is betected, the TAD operation
stops and the line is disconnected.
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