Panasonic KX-TA1232, Service Manual

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(3) DOOR-PHONE UNIT (KX-TA123260)
DOOR-PHONE UNIT consists of the following:
Door-Phone Interface Circuit
Door Opener Circuit
Door-Phone Interface Circuit
Door-Phone Interface Circuit is a circuit which functions the interface between the door-phone
and the PCM highway, and is composed of the following circuits.
Composition:
(a) Circuit for detection whether the door-phone is connected or not.
(b) Current supply circuit
(c) Hook detection circuit
(d) 2-4lines conversion circuit
(e) A/D and D/A conversion circuit(CODEC)IC2
Circuit Operation:
(a) Circuit for detection whether the Door-Phone is connected or not.
When the Door-Phone is not connected, base of Q2 is high.When collector of Q2 is low, input pin
of IC5 is low. When the Door-Phone is connected, base of Q2 is low. When collector of Q2 is high,
input pin of IC5 is high. CPU (IC1) on CPU BOARD gets information through IC5 whether the Door-
Phone is connected or not.
(b) Current Supply Circuit
Q3 supplies current to the Door-Phone line through the transformer (T1).
(c) Hook Detection Circuit
When the call button of Door-Phone isn't pushed, base of Q1 is high. When collector of Q1 is low,
input pin of IC5 is low. When the call button of Door-Phone is pushed, base of Q1 is low. When
collector of Q1 is high, input pin of IC5 is high. CPU (IC1) on CPU BOARD gets information
through IC5 whether the call button is pushed or not.
(d) 2-4Lines Conversion Circuit
This circuit converts 2-line analog signals to 4-line signals.
(e) A/D, D/A Conversion Circuit
This circuit is for converting the analog signals from Door-Phone to the PCM digital signals to
present to the PCM highway, and also converting the data on the PCM highway into the analog
signals to the Door-Phone. This circuit has the power down function and the /A conversion
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