Panasonic KX-FP342BX Service Manual

7.9. NCU SECTION7.9.1. GENERALThis 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 OperationNormally, 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 CIRCUIT1. Circuit OperationThe signal waveform for each point is indicated below. The signal (low level section) input to pin 42 of ASIC IC501 on the digitalboard is read by ASIC and judged as a bell.TEL LINE → PC101 (1, 2 - 4) → IC501 (42)7.9.4. TAM INTERFACE CIRCUITThis circuit is to switch between FAX receiving and the external TAM’s message recording automatically. This circuit consists of anEXT. 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 CIRCUITWhile OFF-HOOK, RLY101 is ON. Q102 turns on by pin (138) of IC501 as well. On the other hand, while ON-HOOK, Q102 turnsOFF by pin (138) of IC501, then the line turns OFF. ON/OFF-HOOK, controlled by pin (138) of IC501, makes the pulse dialoperation possible.IC501 (138) LINE RLY Low Level → CN517 (12) → CN101 (12) → Q102 OFF → RLY101 OFF : DC Loop OFFIC501 (138) LINE RLY High Level → CN517 (12) → CN101 (12) → Q102 ON → RLY101 ON : DC Loop ON147KX-FP342BX