Ncu Section - Panasonic KX-FC255CX-S Service Manual

KX-FC255CX-S
6.7.

NCU Section

General
6.7.1.
It is composed of bell detection circuit, pulse dial circuit, line amplifier, sidetone circuits.
6.7.2. Bell Detection Circuit
1. Circuit Operation
The signal waveform for each point is indicated below. The signal (low level section) input to pin 10 of BBIC IC4 on the digital
board.
TEL LINE → PC101 (1, 2 → 4) → IC4 (10)
6.7.3. On/Off Hook Circuit
Normally (ON-HOOK condition), LINE RELAY (RL101) and Opt Isorator (PC102) is OFF. While OFF-HOOK, RL101 and PC102
turns ON. This LINE RELAY is controlled by pin 83 of IC4 through the Q101. PC102 is controlled by pin 12 of IC4 through the
Q104.
ON-HOOK:
IC4 (83) Low Level → Q101 OFF → RL101 OFF
IC4 (12) Low Level → Q104 OFF → PC102 OFF
6.7.4. Pulse Dial Circuit
The pulse dial is generated by operating the transistor PC102 while OFF-HOOK (RL101 ON) condition.
Make state:
IC4 (12) High Level → Q104 ON → PC102 ON
Break state:
IC4 (12) Low Level → Q104 OFF → PC102 OFF
6.7.5. Line Amplifier and Side Tone Circuit
1. Circuit Operation
The reception signal output from the line transformer T101 is input to pin (2) of IC101 via C130, R138 and then the signal is
amplified at pin (1) of IC101 and sent to the reception system at through the LPF.
OFF-HOOK:
IC4 (83) High Level → Q101 ON → RL101 ON
IC4 (12) High Level → Q104 ON → PC102 ON
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