Sharp AM-900 Service Manual page 93

1.3.4 CML relay
The CML relay switches over connection to the matching transformer
T1 while the FAX is being used.
1.3.5 Matching transformer
The matching transformer performs electrical insulation from the tele-
phone line and impedance matching for transmitting the FAX signal.
1.3.6 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.
1.3.7 Signal selection
The following 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
Line connecting relay and DP generating relay
CML0 H: Line make
L: Line break
Speaker tone mute control signal
SP MUTE H: Muting (Power down mode)
L: Muting cancel (Normal operation)
Speaker volume control signal
VOL A
VOL B
VOL C
VOL A
(the circuit is
located in the
L
control PWB.)
H
L
(Example: Fax signal send)
SURGE
LINE PROTECTION
HI
CIRCUIT
LO
HS
DETECTOR
EXT.TEL
Description
VRSEL1 VRSEL2 matrix
RING./
VOL B VOL C Buzzer DTMF
Receiving
High High
L L -
High
L L Middle Middle
L H Low Low Low
DIODE
ACTIVE
BRIDGE
CHOKE
CI
DETECTOR
+5V
[Signals for status recognition according to input signals]
Signal Name
CI
EXHS
[Other signals]
Signal Name
TXOUT
RXIN
No. Signal Name (CNLIU)
1 RXIN
2 TXOUT
3 CI
4 /EXHS
5 DPON
1.3.8 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.
1.3.9 Power supply and bias circuits
The voltages of +5V and +24VA are supplied from the control PWB
unit.
LIU CONTROL
TXA2
TXOUT TXOUT
TXA1
HI
RXIN RXIN
RIN
LO
VREF
CML CML
EXHS EXHS
CI CI
HI
LO
SPEAKER
+5V
+24VA
DG
Fig. 18
5 – 20
Function
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.
Function
Transmission (DTMF) analog signal output
from modem
Reception (DTMF, others) analog signal input
into modem
No. Signal Name (CNLIU)
6 CML
7 +5V
8 DG
9 +24VA
MODEM
(FM336PLUS)
CI
CML
PB_DATA
IC10
LOGIC IC
BZOUT
SPMUTE
VOLC
VOLB
VOLA
AM-900U
OA-2000