Circuit Description Of Tel/Liu Pwb; Circuit Description Of - Sharp FO-1850 Service Manual

[3] Circuit description of TEL/LIU PWB

(1) TEL/LIU block operational description
1) Block diagram
CML
LINE
EXT.
Handset
HOOK SW
Speaker
2) Circuit description
The TEL/LIU PWB is composed of the following 12 blocks.
1. Surge protection circuit
2. On-hook status detection circuit
3. Dial pulse generation circuit
4. CML relay
5. Matching transformer
6. Hybrid circuit
7. Speaker amplifier circuit
8. Adjustment of voice/ringer volume
9. Signal selection
10. Sensor circuit
11. CI detection circuit
12. Power supply and bias circuit
LIU PWB CONTROL PWB
TXOUT
H
L
CI
DETECTOR
RXIN
TELIN
TELOUT
SPOUT
SPMUTE
P. E
CML
SEL A SEL A
GAIN-C
SEL C
TXCONT
1 1
0
0
1
0
MPX B
VOL A
VOL B
VOL C
MPX C
1
X0
0
X1
X2
X7
+5V
+24VA
DG
VREF
Fig. 6
3) Block description
1. Surge Protection circuit
This circuit protects the circuit from the surge voltage occurring on
the telephone line.
•
The AR1 protects the circuit from the 390V or higher line surge
voltages.
•
The VA1 and VA2 protect the circuit from the 470V or higher
vertical surge voltages.
5 – 9
SIG TX
MODEM
(R144V24)
0
SIG RX
1
RXCONT
MONITOR
1
TXCONT
MPX B XFC-MVP
MPX C
SP MUTE
TEL MUTE
CI
RHS
FO-1850TH
SEL C
GAIN-C
SEL A
CML