Circuit Operation - Panasonic KX-TS820MXB Service Manual

KX-TS820MXB/KX-TS820MXW
4.2.

Circuit Operation

4.2.1. Power supply circuit
The set is powered from the line, 48V/24V.
• Off hook
LINE → Q101 → Q107 → R119 → D106 → D201 → D203 → Vdd (pin7 of IC1)
• On hook
LINE → R101 → R102 → D101 → SW1(pin 5-6) → R13 → D102 → D6 → Vdd (pin7 of IC1)
4.2.2. Bell Ringer Circuit
When the bell signal is input from LINE to T/R (when the telephone rings), the signal is detected and output by micon to the
buzzer via the following path :
• Bell Detection circuit
T / R → C1 → D2 → R2 → Q1 → RINGDET (pin 27 of IC1)
• Bell Output circuit
Pin 15 of IC1 → Q3 → Q2 → R9 → SW2/3 → Buzzer
4.2.3. Telephone Line Interface
4.2.3.1. Circuit operation
• On hook
Q101 is OFF, on-hook condition where DC loop is disconnected and voice signal flow is cut.
• Off hook
During Off-Hook, pin 4_6 of SW1. Q101 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(+) → Q101 → Q107 → R119 → D106 → D101(-) → L102 → R
• Receiving signal flows:
LINE → Q101 → C114 → C301 → R301 → Q301 → C305 → R307 → C306 → Q306 → C310 → R315 → Q308 → C315 →
R318 → SP (handset)
• Transmission signal flows:
MIC (handset) → C402 → R402 → R405 → C405 → Q401 → R409 → C410 → Q107 → Q101 → LINE
• Pulse Dial
A pulse signal switches repeatedly between high and low logic is output from IC1 (pin 11), on and off the line loop, generating the
pulse dial signal.
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