Panasonic KX-TC1200NLB, Service Manual

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JK1 (2): R L4 R120 R152
When the CPU (DSP) detects a ring signal and press the TALK Key on the handset. Q6 turns on
and then RY1 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.
T R160 L4 RY1 R107 T7 R116 D5 L6 R161 R [OFF HOOK]
ON HOOK Circuit:
Q6 is open, RY1 disconnected as to cut the DC loop current and to cut the voice signal. The unit
is consequently in an on-hook
condition.
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal.
As for this unit, TX signal feed back from Q11 is canceled by the cancellor circuit of AGC.
16.6. Transmitter/Receiver
Base Unit and Handset are mainly consists of RF(Radio Frequency) IC and CPU.
Base Unit and Handset transmit/receive voice signal and data signal through the antenna on
carrier frequency.
Signal Pass :
*Refer to CDL TX/RX in
Signal Route ().
16.6.1. Base to Handset
Circuit Operation:
The voice signal input from the TEL LINE interface goes to RF IC as shown in
BLOCK DIAGRAM (BASE UNIT) ().
In the talk mode (off-hook) condition, the telephone line voice signal passes through D2, D3, D4,
D5, RY1 (Relay), R107 and T7.
The other party's voice signal is coupled with T7 and amplified by Q11 and led to IC3-B (OP
Amplifier device).
And the signal goes through the compressor of RF IC, it is output to transmitter circuit.
The signal of the data sent to the handset is applied in the anode of the variable capacitor diode
(VARICAP : DV1).
The capacitor of VARICAP is changing in accordance with the voice signal from telephone line
interface or TX DATA signal from
CPU. Therefore, the carrier frequency which is generated by TXVCO will be changing, and
Frequency modulated RF
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