Oki OKIOFFICE44 Service Manual page 268

A3.1.4 R44 Circuit Diagram
1. Block diagram
The audio monitor circuit consists of IC11 (analog switch IC) and IC5 (amplifier) generates the
following audio monitor.
• Line monitoring
• Buzzer signals
Figure A3.1.4 shows the block diagram of audio monitor circuit.
2. Function
1) Line monitoring
Send and receive signals are input from the transformer on the NCU board to this circuit as
a R signal and the signal power is input to the IC11. The IC11 adjusts the monitor
volume by MONC0, MONC1 and MONC2 signal under the control of IOGA3. Output
(high and low) from IC11 passes through the amplifier and is fed to the 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
2) Buzzer control
Alarm and other signals are input from CPU to this circuit as BZ signals. The various
buzzer signals are sounded under the control of CPU.
+5 V
TR1
RM
0 VA
Board Descriptions
monitor will be switched off automatically after the elapse of specified time (about 5
sec).
CPU
BZ
MONC0
MONC1
MONC2
IC2
IOGA3
Figure A3.1.4 Block Diagram of Audio Monitor Circuit
IC11
Amplifier
Analog
switch
0 VA
A - 26 OKIOFFICE 44 Serv. Man., P/N 59276801
CN9
Speaker
1
IC5
2
0 V