Circuit Description Of Tel/Liu Pwb - Sharp FACSIMILE FO-4500 Service Manual

[3] Circuit Description of TEL/LIU PWB

(1) TEL/LIU block operational description
1) Block diagram
E
T1
L
CURRENT
L1
SENSOR
H
H
DUMMY
L2
L&C
L
S
T2
T1
T2
H
SPEAKER
L
2) Circuit description
The TEL/LIU PWB is composed of the following 12 blocks.
1. Surge protection circuit
2. Noise filter
3. On-hook status detection circuit
4. Dial pulse generation circuit
5. CML relay
6. Matching transformer
7. Hybrid circuit
8. Speaker amplifier
9. Adjustment of voice volume
10. Signal selection
11. Cl detection circuit
12. Power supply and bias circuit
H
L
~ –
TAX
PULSE
FILTER
~ +
SHUNT
CIRCUIT
H
CI DETECTOR
L
SPARK
QUENCH
TEL/LIU PWB
HS
CML
E-RLY
DP
MPX A
N.C.
N.C.
N.C.
H
SIGTX
L
H
SIGRX
L
ACTIVE
CHOKE
N.C.
N.C.
H
N.C.
L
DPMUTE
CI
SPOUT
SPMUTE
DG
DG
+5V
+12V
AG
AG
Fig. 8
3) Block description
1. Surg 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.
•
The ZD4 and ZD5 control the voltages generated on the sec-
ondary side of matching transformer to 2V.
•
The VA3 protect the circuit from 100V or higher line surge
voltages.
2. Noise filter
The noise filter comprises the RF choke coil, L1, L2, L3 and
capacitor C16.
•
The L1, L2, L3 and C16 prevent unnecessary radio noises from
being transmitted from the telephone line.
•
The C16 prevent radio pickup from the telephone line.
5 – 19
CONTROL PWB
CNLIU-18
CNLIU-22
CNLIU-13
CNLIU-20
CNLIU-9
CNLIU-7
CNLIU-8
CNLIU-10
CNLIU-16
CNLIU-17
CNLIU-19
CNLIU-23
CNLIU-24
CNLIU-15
CNLIU-21
H
CNLIU-14
X0
SPOUT
X1
X2
L
CNLIU-12
CNLIU-1
DG
CNLIU-3
CNLIU-2
+5V
CNLIU-5
+12V
CNLIU-4
AG
CNLIU-6
FO-4500H
CML
TELMUTE
VOLCNT
MPX A
CPU
MPX B
VRSEL1
VRSEL2
SPMUTE
TXOUT
MODEM
RXIN
RHS
DP
SDT
HS1
DT
GATE
DT3
ARRYA
CI
VOLA
VOLB
BZOUT