KX-MB2110RUW, KX-MB2130RUW, KX-MB2170RUW, KX-MB2117RUB, KX-MB2137RUB, KX-MB2177RUB - Panasonic Copying Equipment Service Manual (repair manual). Page 35

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KX-MB2110RUW/ KX-MB2130RUW/ KX-MB2170RUW/ KX-MB2117RUB/ KX-MB2137RUB/ KX-MB2177RUB

 NCU: (Network Control Unit)
Requires for connecting computers to public communication networks and send a dial signal to call the other party.  

NCU is the with the telephone line. It is composed of EXT. TEL. Line Relay (RLY100), Bell Detection Circuit, Pulse Dial Circuit, Line
Amplifier and Side Tone Circuit, Calling Line Identification Circuit (FSK_Bellcore), Calling Line Identification Circuit (DTMF), Calling
Line Identification Circuit (FSK_ETSI), Remote FAX Activation Circuit and TAM Interface Circuit. The following is a brief explanation
of each circuit.

1. Circuit Operation

Normally, this relay switches to the external telephone side and switches to the open side while OFF-HOOK.
IC300 (P23) High Level

Q201 ONRLY100 (ON)

1. Circuit Operation 

The signal waveform for each point is indicated below. The signal (low level section) input to IC300 (W25).
TEL LINE 

 PC103 (1, 2  4)  IC300 (W25)

The pulse dial is generated by operating the transistor Q201 while OFF-HOOK (RLY100 ON) condition.
Make state:
IC300 (P23) High Level 

 Q201 ON  RLY100 ON

Break state:
IC300(P23) LOW Level 

 Q201 OFF  PC100 OFF

1. Circuit Operation

The reception signal output from the line transformer T100 is input to pin (2) of IC201 via C256, R224 and then the signal is
amplified at pin (1) of IC201 and sent to the reception system at through the LPF.