Board Descriptions A - 23 OF 5300/5600 Serv Man, P/N 59278301A3.2.4 M17 Circuit Diagram1. Block diagramThe audio monitor circuit consists of IC11 (analog switch IC) and IC5 (amplifier) gener-ates the following audio monitor.• Line monitoring• Buzzer signalsFigure A3.2.4 shows the block diagram of audio monitor circuit.2. Function1) Line monitoringSend and receive signals are input from the transformer on the NCU board to thiscircuit as RM signal and the signal power is input to the IC11. The IC11 adjuststhe monitor volume by MONC0, MONC1 and MONC2 signal under the control ofIOGA3. Output (high and low) from IC11 passes through the amplifier and fed tothe speaker as a SP signal.• MONC0/MONC1/MONC2 signal : Volume control signal.Note: In case of transmission mode, the monitor will be available during dialing,but the monitor will be switched off automatically after the elapse of speci-fied time (about 5 sec).2) Buzzer controlAlarm and other signals (key touch etc.) are input from CPU to this circuit as BZsignal. The various buzzer signals are sounded under the control of CPU.Block Diagram of Audio Monitor Circuit (Figure A3.2.4)IC11IC2IOGACPURMAnalogswitch IC5Amplifier CN812SpeakerBZMONC0MONC1MONC20V0VA+5 V0VAfrom modemTR1
