Panasonic KX-FP81BX Service Manual page 165

KX-FP81BX / KX-FP81CX / KX-FP82CX
6.8.5. LINE AMPLIFIER AND SIDE TONE CIRCUIT
1. Circuit Operation
The reception signal output from the line transformer T101 is input to pin (2) of IC101 via C136, R111, C111 and R158 and then
the signal is amplified at pin (1) of IC101 and sent to the reception system at 11.6dB.
The transmission signal goes through C571 and R579 and enters IC511-pin (2), where the signal is amplified to about 7.4dB.
Then, it is output from pin (1) of IC101 and transmitted to T101 via C117 and R110. If the side tone circuit is not applied, the
transmission signal will return to the reception amplifier via C136, R111, C111 and R158. When the side tone circuit is active,
the signal output from IC101 pin (1) passes through C117, R113, C113, C112 and R112 and goes into the amplifier IC101 pin
(3). This circuit is used to cancel the transmission return signal.
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