Service manual

FO-4700U
FO-47UC
5 – 18
3. Dial pulse generation ciruit
The pulse dial generation circuit comprises the photo-coupler PC2,
polarity guard REC, and transistor Q3.
The dial pulse turns on CML, controls the base current of PC2 and
supplying the DP signal to the photo-coupler PC2, and generates the
DP signal by making the TEL circuit make and break.
4. CML relay
The CML relay switches over connection to the matching transformer
T1 while the FAX is being used.
5. Matching transfomer
The matching transformer performs electrical insulation from the tel-
ephone line and impedance matching for transmitting the FAX signal.
6. Hybrid circuit
The hybrid circuit performs 2-wire-to-4-wire conversion using the IC
of operational amplifier, transmits the voice transmission signal to the
line, and feeds back the voice signal to the voice reception circuit as
the side tone.
7. Signal selection
The follwing signals are used to control the transmission line of FAX
signal. For details, refer to the signal selector matrix table.
[Control signals from output port]
Signal Name Description
CML
SP MUTE
VOL A
VOL B
VOL C
(the circuit is located in
the control PWB.)
Line connecting relay and DP generating relay
H: Line make
L: Line brask
Speaker tone mute control signal
H: Muting (Power down mode)
L: Muting cacel (Normal operation)
Speaker volume control signal,
L
H
L
VOL A
L
L
L
VOL B
L
L
H
VOL C
VRSEL1 VRSEL2 matrix
–
High
Low
Buzzer DTMF
High
Middle
Low
High
Middle
Low
RING./
Receiving
TXMUTE
(the circuit is located in
the control PWB.)
TXOUT mute signal
H: Signal sending, when transmitting
L: During reception, transmission mute,
(durung standby)
GAIN-C
(the circuit is located in
the control PWB.)
Reception gain switching signal
L: When connected to line, 1:1 gain
H: When not connected to line, 1:1 gain
BZCONT
(the circuit is located in
the control PWB.)
Speaker output signal switching
H: Buzzer signal output
L: When monitoring line signal
[SIgnals for status recognition according to input signals]
Signal Name Function
CI
EXHS
Incoming call (CI) detection signal
H: The handset or external telephone is in the
on-hook state.
L: The handset or external telephone in the off-
hook state.
H: Active choke ON
L: Active choke OFF
DPON
[Other signals]
Signal Name Function
TXOUT
RXIN
Transmission (DTMF) analog signal output from
modem
Reception (DTMF, others) analog signal input into
modem
8. CI detection circuit
The CI detection circuit detects the CI signals of 15.3 Hz to 68 Hz.
A CI signal, which is provided to the photo-coupler PC1 through the
C1 (0.82 uF), R6 (22K), and ZD3 and R5 (13K) when the ring signal is
inputted from the telephone line.
9. Power supply and bias circuits
The voltages of +5V and +24VA are supplied from the control PWB
unit.
NO Signal Name(CNLIU)
1 RXIN
2 TXOUT
3CI
4 EXHS
5 DPON
NO Signal Name(CNLIU)
6 CNL
7 +5V
8DG
9 +24VA