Oki OKIOFFICE 84 Service Manual page 386

A3.1.3 R51 Circuit Diagram (Page 3/12)
1. Block diagram
The audio monitor circuit on page 3/12 that consists of IC11 (analog switch IC) and IC5 (amplifier) generates the
following audio monitor.
l
Line monitoring
l
Buzzer signals
Figure A3.1.3 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 IOGA4. 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 monitor will be switched
off automatically after the elapse of specified time (about 5 sec).
2) Buzzer control
Alarm and other signals are input from IOGA4 to this circuit as BZ signals. The various buzzer signals are
sounded under the control of IOGA4 (CPU).
Service Guide OKIOFFICE 84
Chapter A Board Descriptions
Page: 231