Panasonic KX-TCD540NZM Service Manual page 117

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ON/OFF hook circuit
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Audio circuits
Bell & Clip (: Calling Line Identification Presentation: Caller ID) signal detection:
In the standby mode, Q4 is open to cut the DC loop current and decrease the ring
load.
When ring voltage appears at the TP21 (A) and TP19 (B) leads (when the telephone
rings), the signal is transferred as follows;
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A C13 R17
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B C12 R16
ON/OFF hook circuit:
In the standby mode, Q4 is open, and connected as to cut the DC loop current and
to cut the voice signal. The unit is consequently in an on-hook condition.
When IC2 detects a ring signal or press SP Key or pick up Curl Cord Handset or
press the TALK Key onto the handset, Q5 turns on and then Q4 turns on, thus
providing an off-hook condition (active DC current flow through the circuit) and the
following signal flow is for the loop current.
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A D3 Q4
21.4. Transmitter/Receiver
Base Unit and Cordless Handset mainly consist of RF Module and DECT BBIC.
Base Unit and Cordless Handset transmit/receive voice signal and data signal
through the antenna on carrier frequency.
Signal Pass:
*Refer to SIGNAL ROUTE
).
21.4.1. Transmitter Block
R24 IC2 Pin 107 (CID IN +)
R32 IC2 Pin 112 (CID IN -)
R34 Q8 R45
(
R46 D3 B [OFF HOOK]
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