Oki OKIOFFICE84 Maintenance Manual page 274

R51
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.
•
•
Figure A3.1.3 shows the block diagram of audio monitor circuit.
2. Function
1)
2)
+5 V
RM
From MODEM
circuit
0 VA
40672201TH Rev. 4
Line monitoring
Buzzer signals
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).
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).
IC2
IOGA4
TR513
IC2
IOGA4
Figure A3.1.3 Block Diagram of Audio Monitor Circuit
IC11
BZ
MONC0
Analog
switch
MONC1
MONC2
A3 - 4
CN9
Amplifier
1
IC5
2
0 VA 0 V
Speaker