Panasonic KX-FT981LA-B Service Manual page 38

KX-FT981LA-B / KX-FT987LA-B
6.7.5. Line Amplifier and Side Tone Circuits
1. Circuit Operation
The reception signal received as output from line transformer T101 is given as input to C108, R109 and IC101(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 CN101 pin (6), and output to the TEL line through T101. Without a side tone circuit, the
transmission signal would return to the reception amplifier via C113 and R114. Here, the signal output from CN101 pin (6)
passes through C113, R113, R112, C109 and R110, and enters the amplifier IC101 pin (2). This is used to cancel the return
portion of the transmission signal. This is the side tone circuit.
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