Panasonic KX-FP362BX Service Manual

7.9.5. LINE AMPLIFIER AND SIDE TONE CIRCUIT1. Circuit OperationThe reception signal output from the line transformer T101 is input to pin (2) of IC101 via C112 and R112 and then the signalis 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 24.8dB.Then, it is output from pin (1) of IC101 and transmitted to T101 via C125 and R121. If the side tone circuit is not applied, thetransmission signal will return to the reception amplifier via C112 and R112. When the side tone circuit is active, the signaloutput from IC101 pin (1) passes through C125, R123, C122, C115 and R115 and goes into the amplifier IC101 pin (3). Thiscircuit is used to cancel the transmission return signal.7.9.6. AUTO DISCONNECT CIRCUIT1. FunctionThis circuit is used to detect that the telephone connected in parallel to the same line is OFF-HOOK while the unit picks up theline.2. Circuit OperationIf the line is picked up, C158 is charged by the following path shown below.Tip (Ring) → D107 → R160 → D108 → R161 → Q110→ PC103If a telephone connected in parallel goes into OFF-HOOK status, the base of Q110 becomes low and PC103 turns OFF.When the line is connected, Q110 and PC103 turn on, then pin (97) of IC505 (MODEM) on the digital board becomes low. Onthe other hand, When the line is disconnected, Q110 and PC103 turn off, then the pin (97) of IC505 (MODEM) becomes high.7.9.7. CPC (Calling Party Control) DETECTION CIRCUIT1. FunctionThis circuit detects the signal (cuts the current ) output from the converter when the other party finishes ICM recording and goesinto the ON-HOOK status.TAD detects this signal and disconnects the line. When the TAD is operating, pin (4) of PC105 becomes a low level.While detecting the CPC signal, pin (4) of PC105 becomes a high level. When the CPC signal is detected, the TAD operationstops and the line is disconnected.150KX-FP362BX