Circuit Operation - Panasonic KX-TSC62SXB Service Manual

KX-TSC62SXB/KX-TSC62SXW
4.2.

Circuit Operation

4.2.1. Bell Detector Circuit
When the bell signal is input from LINE to T/R (when the telephone rings), the signal is output at the buzzer via the following
path :
T/R  C201  R201  IC201 (pin8)  IC201 (pin5)  R204  SW201  Buzzer
4.2.2. Telephone Line Interface
4.2.2.1. Circuit operation
• On hook
Q301 is OFF, on-hook condition where DC loop is disconnected and voice signal flow is cut.
• Off hook
During Off-Hook, pin 1-3 of SW301 and Q301 is ON, providing an off-hook condition (active DC current flow through the circuit)
and the following is the signal flow :
T  POS101  L101  D101(+)  Q301  Q401  R412  D413  D101(-)  L102  R
• Receiving signal flows:
LINE  Q301  C402  C431  R431  Q431  C434  C438  R443  Q433  C440  SP (handset)
• Transmission signal flows:
MIC (handset)  C422  R422  R423  C425  Q422  C429  R429  Q401  Q301  LINE
• Pulse Dial
A pulse signal switches repeatedly between high and low logic is output from IC801 (pin 56), on and off the line loop, generating
the pulse dial signal.
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