Service manual

[3] Circuit description of TEL/LIU PWB
(1) TEL/LIU block operational description
1) Block diagram
Fig. 6
2) Circuit description
The TEL/LIU PWB is composed of the following 10 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. Sensor circuit
9. Cl detection circuit
10. 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 voltages.
H
L
HS DETECTOR
CML
CI DETECTOR
0
1
SPEAKER
TEL
LINE
+5V
+24VA
DG
TEL MUTE
CI
TEL MUTE
CI
BZCONT
RCVOL
TXCONT
BZCONT
VOL C
VOL B
VOL A
TELOUT
TEL IN
EXT.
HANDSET
RXIN
TXOUT
CML
HS
GAIN-C
TXCONT
SIGTX
SIGRX
0
1
RCVOL
0
1
GAIN-C
CML
HS
XFCR-MVP
MODEM
(R96DFXL-CID)
CONTROL PWBTEL/LIU PWB
SP MUTEI
UX-510U/UX-510C/UX-500U
UX-500C/FO-1460U
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