Panasonic KX-FT937LA-B Service Manual page 38

KX-FT937LA-B
6.7.5. Line Amplifier and Side Tone Circuits
1. Circuit Operation
The reception signal received as output from line transformer T1 is given as input to R81, C17, R13 and IC2(2).
Then it is input to the reception system at an amplifier gain of 2.5 dB from pin (2).
The transmission signal is input from CN1 pin (5), and output to the TEL line through C11, R16, IC2(6,7) and T1. Without a
side tone circuit, the transmission signal would return to the reception amplifier via C28, R27 and R26. Here, the signal output
from CN1 pin (5) passes through C28, R23, R22, R82, C21 and R18, and enters the amplifier IC2 pin (3). This is used to can-
cel the return portion of the transmission signal. This is the side tone circuit.
6.7.6. 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 detected, the TAD operation stops
and the line is disconnected.
38