Sharp FO-3150, Руководство по обслуживанию

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FO-3150U/C
[4] Circuit description of TEL/LIU and Hook
SW PWB
1. TEL/LIU block operation description
(1) Block diagram
(2) Circuit description
The TEL/LIU PWB is composed of the following 8 blocks.
1. Surge protection circuit
2. On-hook status detection circuit
3. Dial pulse generation circuit
4. CML relay
5. Matching transformer
6. Signal selection
7. CI detection circuit
8. Power supply and bias circuits
(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 AR3 protects the circuit from the 470V or higher vertical surge
voltage.
2) On-hook status detection circuit
The on-hook status detection circuit detects the status of the hook
switch (RHS) of built-in telephone, and the status of the hook of a
telephone externally connected.
• The status of on-hook switch (RHS) is determined from the logical
level of RHS signal. (RHS is in the hook SW PWB)
RHS LOW: ON-HOOK
RHS HIGH: OFF-HOOK
• External telephone hook status detection circuit (HS)
This circuit comprises the photo-coupler PC1, resistors R7 and R8,
Zener diodes ZD3 and ZD4.
When an external telephone is connected and enters the on-hook
mode, the LED of photo-coupler PC1 emits light and the light receiv-
ing element turns on.
HS LOW: EXT. TEL OFF-HOOK
HS HIGH: EXT. TEL ON-HOOK
3) Dial pulse generation circuit
The pulse dial generation circuit comprises the CML relay.
4) CML relay
The CML relay switches over connection to the matching transformer
T1 while the FAX or built-in telephone is being used.
Fig. 27
C
LIU PWB CONTROL
DG
DG
DG
DG
DG
RTLoop
DG
DG
EXIT
LINE
RX
TX
1, 0
C I
Mi c/
CML
HS-
L PF
0, 1
SIGTX SPKRP
(20438 I/A)
0,
1,0
1,1
0
ect
SIGRX
Mut e,0,- 6, -12dB
C I
T XOUT
SIN
SP Out Enable
LninS el
D A C
HS
0 ,2 0 ,25, 30dB
0, 6dB
MICP
1, 1
S OUT
MICMUTE
A D C
0, 4dB
0, 0
OPAMP
OPAMP
SW1
HOOK-SW PWB
OPAMP
OPAMP
E
B
C
3 5
4
T1
E
B
C
E
B C
E
B
C
SPMUTE
SPOUT
(H:MUTE)
DETECTOR
+24V
+5V
DG
SPMUTE
DTMFMUTE
TELMUTE
MICMUTE
RCVOL
RHS-
DETECTOR
RXIN
Mic Enable
LINE
OUT
Sel
Line Out Enable
Line In Enable
(H:MUTE)
(H:MUTE)
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