Ncu Section; General; Ext. Tel. Line Relay (Rly100); Bell Detection Circuit - Panasonic KX-MB2085CXW Service Manual

6.4.

NCU Section

6.4.1.

General

NCU is the with the telephone line. It is composed of Bell detection circuit, Pulse dial circuit, Line amplifier and sidetone circuits. The
following is a brief explanation of each circuit.
6.4.2.

EXT. TEL. Line Relay (RLY100)

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)
6.4.3.

Bell Detection Circuit

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)
6.4.4.

Pulse Dial Circuit

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
6.4.5.

Line Amplifier and Side Tone Circuit

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.
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KX-MB2085CXW/KX-MB2090CXW