Panasonic KX-TMC40JX-W, Service Manual

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voltage appears at the Tip (T) and Ring (R) leads (When the telephone rings), the AC ring
voltage is transferred as follows:
T L101 R2 C2 Q1 IC201 pin 27.
When the CPU (DSP) detects a ring signal, Q103 turns on, thus providing an off-hook condition
(active DC current flow through the circuit) and the following signal flow is for the voice signal.
T D101 Q103 R119 C110 R117 R116 D103 D101 L102 P0S101
R.
ON HOOK Circuit:
Q103 is open, Q103 is connected as to cut the DC loop current and to cut the voice signal. The
unit is consequently in an on-hook condition.
SPECIFICATIONS
In the on-hook state (idle), the current flows between the telephone line and the unit is as
follows:
T L101 R2 C2 R4 C3 R2 L102 R.
The DC component is blocked by C2, C3: thereby providing an on-hook condition.
The AC interface impedance is over 100k ; thus, satisfying the telephone company
requirements.
9.16. Initializing Circuit
Function:
This circuit is used for to initialize the microcomputer when it incorporates an AC adaptor.
Circuit Operation:
The set can operate beyond point A in the circuit voltage diagram.