Ncu Section - Panasonic KX-FT72BR-G Service Manual

5.8.

NCU SECTION

5.8.1. GENERAL
This section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL Line relay (RLY1),
bell detection circuit, EXT TEL selection circuit, pulse dialing circuit, line amplifier, sidetone circuits and multiplexer.
5.8.2. LINE RELAY (RL1)
Circuit Operation
Normally, this relay switches to the external telephone side (Break) and switches to the open side (make) when the unit starts
facsimile communication. Pulse dialing is also performed by ON/OFF of the relay.
[IC1 (99) High Level → CN9 (8)] → CN1(8) → Q3 ON → RL1 (make)
5.8.3. BELL DETECTION CIRCUIT
Circuit Operation
The signal waveform for each section is indicated below. The signal (low level section) input to pin 19 of ASIC IC4 on the digital
board is read.
TEL LINE → PC1 (1, 2 - 4) → CN1(6) → [CN9(6) → R119 → IC1(56)]
5.8.4. PULSE DIALING
[IC1 (99) High Level → CN9 (8)] → CN1 (8) → Q3 ON → PC1 ON (make)
Refer to # 013 on the PROGRAM MODE TABLE (P.54)
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KX-FT72BR-G