Panasonic KX-FM330GR Service Manual page 216

KX-FP320G / KX-FM330G
6.9.6. SIDE TONE CIRCUIT
1. Function
A sidetone is the returning of the TX signal to the RX signal. The sidetone circuit uses a bridge circuit to attenuate the sidetone.
Howling may occur if the attenuation of the sidetone is inadequate.
2. Circuit Operation
The TX signal is output to the circuit along the route from the IC10-1pin → C37 → R58 → R57 → T1 → TEL LINE. However,
if balance is lost in the bridge as shown below, a voltage occurs between the IC10-5 pin and 6 pin and a sidetone results.
Because the balance cannot be maintained completely at all frequencies in the audio range, some sidetones always occur.
6.9.7. REMOTE FAX ACTIVATION CIRCUIT
1. Function
Another telephone connected to same line activates the unit to the FAX mode by using a DTMF signal.
2. Signal Path
TEL Line → T2 → C115 → R154 → IC5 (61→67) → R167 → C134 → IC2 (10 → 11) → C68 → CN7 (9) → {CN501 (9) → C701
→ IC801(3→4) → C943 → J604 → C603 → IC5(60)}
{ }........Digital board
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