Circuit Description Of Tel/Liu And Hook Sw Pwb - Sharp UX-4000M - UX 4000 B/W Laser Printer Service Manual

[3] Circuit description of TEL/LIU and Hook
SW PWB
1. TEL/LIU block operation description
(1) Block diagram
CML
H
HS DETECTOR
LINE
L
EXT.
TEL MUTE
(H:MUTE)
RX
TX
SPEAKER
CI
(2) Circuit description
The TEL/LIU PWB is composed of the following 9 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. Signal selection
8. CI detection circuit
9. Power supply and bias circuit
(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 voltage.
LIU PWB CONTROL PWB
HS
CML
GAIN -C
TXOUT
CI DETECTOR
0:CID
RXIN
1:RX
0:MID
TEL IN
1:HIGH
TELOUT
SP MUTE
(H:MUTE)
+5VA
+24V
DG
SP OUT
ENABLE
SIGTX SPKRP-P
SP
DRIVER
TELOUT MICP
MIC IN LPF
MIC
GAIN
0, 20, 25, 30dB
SIXGRX LINE IN
LINE IN LPF
LNLNSEL
LINE
DRIVER
LINE OUT
SPOUT
MUTE, 0,
–6, –12dB
LINE OUT
ENABLE
BZCONT
0:LINE
1:BZ
HOOK-SW PWB
Fig. 23
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 PC2, resistors R1 and R2,
Zener diodes ZD1 and ZD2.
When an external telephone is connected and enters the on-hook
mode, the LED of photo-coupler PC2 emits light and the light receiv-
ing element turns on. The status signal HS is input to the pin119 of
(SH7041) (IC5: control PWB).
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.
5 – 21
UX-4000MU
FO-2950MU/C
(0:1)
MIC ENABLE
(1:0)
(0:0)
DAC SIN
(1:1)
DAC GAIN
0, 6dB
MIC
ENABLE
1
0
SOUT
ADC
ADC, GAIN
1
0, –4dB
0
LINE IN
ENABLE
(0:0)
(1:1)
(1:0)
BZOUT
IC15 LR38784A
BZCONT
RCVOL
GAIN-C
VOL C
VOL B
CML
VOL A
SP MUTE HS
IC5 SH2
TEL MUTE
(7041)
CI
RHS