Panasonic KX-T7565AL, Service Manual

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8.7. HANDSET CIRCUIT
(1) TRANSMISSION SIGNAL PATH
The analog input signal for the handset microphone is changed to a digital signal and sent through the telephone line via the
following path:
(2) RECEPTION SIGNAL PATH
The digital input signal from the telephone line is changed to an analog signal by IC3 and sent to the receiver via the following
path:
(3) CIRCUIT DIAGRAM FOR TRANSMISSION / RECEPTION SIGNAL PATH.
8.8. SPEAKER-PHONE CIRCUIT
(1) FUNCTION
This circuit controls the automatic switching of the transmitted and received signals to and from the telephone line, when the
unit is used in the hands-free mode.
(2) CIRCUIT OPERATION
The speakerphone can only provide a one-way communication path.
In other words, it can either transmit an outgoing signal or receive an incoming signal.
This switching circuit is contained in IC8 and consists of a Voice Detector, Tx Attenuator, Rx Attenuator, Comparator and
Attenuator Control. The circuit analyzes whether the Tx (transmit) or Rx (receive) signal is louder, and then it processes the
signals so that the louder signal is given precedence.
The Voice Detector provides a DC input to the Attenuator Control corresponding to the Tx signal. The Comparator receives a
Tx and Rx signal, and supplies DC input to the Attenuator Control corresponding to the Rx signal. The Attenuator Control
provides a control signal to the Tx and Rx Attenuator to switch the appropriate signals ON and OFF. The Attenuator Control also
detects the level of the volume control to automatically adjust the volume for changing ambient conditions.
(3) CONTROL SIGNAL PATH
Control signals for transmission and reception are input to IC8 via the following path:
(Transmission Control Signal Path)
(Reception Control Signal Path)
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KX-T7565AL / KX-T7565AL-B