Panasonic KX-TG6700B Service Manual page 29

4.8.5. Sending Signal
The voice signal from the microphone is input to DSP (89, 90). CN331 is the headset jack. When the headphone is connected,
the Q331 detect it. The input from the microphone of the Handset (MIN, MIP) is cut and the microphone signal from the headset
is input to DSP (94). Also the power for the microphone is supplied from DSP (78) and the power is turned OFF on standby.
4.8.6. Reception Signal
The voice signal from the Base Unit is output to DSP (97). This signal is led to the headset jack (CN331). The signal through the
headset jack and the other signal output from DSP (96) drives the speaker. When the headset is inserted to the jack, the voice
signal is cut at the jack, so the sound does not come out from the speaker, but from the headset only.
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KX-TG6700B/KX-TG6702B/KX-TGA670B