Panasonic KX-FPC135 Service Manual page 190

KX-FPC135 / KX-FPC141
7.8.5. LINE AMPLIFIER AND SIDE TONE CIRCUITS
1. Circuit Operation
The reception signal output from the line transformer T101 is input to pin (6) of IC101 via C126 and R131, and then the signal
is amplified at pin (7) of IC101 and sent to the reception system at 12dB (KX-FPC135), 10dB (KX-FPC141).
The transmission signal goes through C131 and R137 and enters IC101-pin (2), where the signal is amplified to about 18dB
(KX-FPC135), 16.5dB (KX-FPC141). Then, it is output from pin (1) of IC101 and transmitted to T101 via C133 and R125. If the
side tone circuit is not applied, the transmission signal will return to the reception amplifier via C126 and R131. When the side
tone circuit is active, the signal output from IC101 pin (1) passes through C133, R128, R129, C124, C123 and R127 and goes
into the amplifier IC101 pin (5). This circuit is used to cancel the transmission return signal.
7.8.6. AUTO DISCONNECT CIRCUIT (KX-FPC141 only)
1. Function
This circuit is used to detect that the telephone connected in parallel to the same line is OFF-HOOK while the unit picks up the
line.
2. Circuit Operation
If the line is picked up, C104 is charged by the following path shown below.
Tip (Ring) → D101 → R103 → D102 → R105 → Q102 → PC102
If a telephone connected in parallel goes into OFF-HOOK status, the base of Q102 becomes low and PC102 turns OFF.
When the line is connected, Q102 and PC102 turn on, then pin (153) of IC501 (ASIC) on the digital board becomes low. On
the other hand, When the line is disconnected, Q102 and PC102 turn off, then the pin (153) of IC501 (ASIC) becomes high.
7.8.7. CPC (Calling Party Control) DETECTION CIRCUIT (KX-FPC141 only)
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 PC104 becomes a low level.
While detecting the CPC signal, pin (4) of PC104 becomes a high level. When the CPC signal is detected, the TAD operation
stops and the line is disconnected.
190