Ncu Section - Panasonic KX-FT937LA-B Service Manual

6.7.

NCU Section

6.7.1. General
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 23 of ASIC IC1 on the digital
board.
TEL LINE → PC1 (1, 2 → 4) → CN1 (11) → {CN2 (11) → IC1 (23)}
Note:{ }: inside the digital board
6.7.3. ON/OFF Hook Circuit
Normally (ON-HOOK condition), LINE RELAY (RLY1) is OFF. While OFF-HOOK, RLY1 turns ON. This LINE RELAY is con-
trolled by pin 130 of IC1 through the Q7.
ON-HOOK:
IC1 (130) Low Level → Q7 OFF → RLY1 OFF
OFF-HOOK:
IC1 (130) High Level → Q7 ON → RLY1 ON
6.7.4. Pulse Dial Circuit
Make state:
IC1 (130) High Level → Q7 ON → RLY1 ON
Break state:
IC1 (130) Low Level → Q7 OFF → RLY1 OFF
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KX-FT937LA-B