Ncu Section - Panasonic KX-FP342BX Service Manual

7.9.

NCU SECTION

7.9.1. GENERAL
This section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL line relay (RLY101),
bell detection circuit, pulse dial circuit, TAM interface circuit, line amplifier and sidetone circuits and a multiplexer.
7.9.2. EXT. TEL. LINE RELAY (RLY101)
1. Circuit Operation
Normally, this relay switches to the external telephone side (break) and switches to the open side (make) while OFF-HOOK.
{ IC501 (138) High Level → CN517 (12) High Level } → CN101 (12) High Level → Q102 ON → RLY101 (make)
7.9.3. BELL DETECTION CIRCUIT
1. Circuit Operation
The signal waveform for each point is indicated below. The signal (low level section) input to pin 42 of ASIC IC501 on the digital
board is read by ASIC and judged as a bell.
TEL LINE → PC101 (1, 2 - 4) → IC501 (42)
7.9.4. TAM INTERFACE CIRCUIT
This circuit is to switch between FAX receiving and the external TAM's message recording automatically. This circuit consists of an
EXT. TAM OFF-HOOK detect circuit, monitor transformer, multiplexer, amplifier, and VOX detect circuit.
For details, please refer to TAM INTERFACE SECTION (P.152).
7.9.5. PULSE DIAL CIRCUIT AND ON / OFF HOOK CIRCUIT
While OFF-HOOK, RLY101 is ON. Q102 turns on by pin (138) of IC501 as well. On the other hand, while ON-HOOK, Q102 turns
OFF by pin (138) of IC501, then the line turns OFF. ON/OFF-HOOK, controlled by pin (138) of IC501, makes the pulse dial
operation possible.
IC501 (138) LINE RLY Low Level → CN517 (12) → CN101 (12) → Q102 OFF → RLY101 OFF : DC Loop OFF
IC501 (138) LINE RLY High Level → CN517 (12) → CN101 (12) → Q102 ON → RLY101 ON : DC Loop ON
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KX-FP342BX