Panasonic KX-TCD420GS Service Manual page 63

20.3. Telephone Line Interface
<Function>
- Bell signal detection
- Clip signal detection
- ON/OFF hook circuit
- Audio circuits
Bell & Clip (: Calling Line Identification Presentation: Caller ID) signal detection:
In the standby mode, Q2 is open to cut the DC loop current and decrease the ring load.
When ring voltage appears at the TP3 (A) and TP40 (B) leads (when the telephone rings), the signal is
transferred as follows;
- A C25 R40
[CLIP]
- B C24 R39
[CLIP]
- A C2 IC1
- B D2 D3
ON/OFF hook circuit:
In the standby mode, Q2 is open, and connected as to cut the DC loop current and to cut the voice
R45 IC5
R44 IC5
IC8 (81) [BELL]
R1 IC1 IC8 (81) [BELlL]
C28 R47 C29
C28 R47 C29
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R49 IC8 (136)
R49 IC8 (136)