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[3] Circuit description of TEL/LIU PWB
(1) TEL/LIU block operational description
1) Block diagram
2) Circuit description
The TEL/LIU PWB is composed of the following 7 blocks.
1. Speech circuit section
2. Dial transmission section
3. Speaker amplifier section
4. Ringer circuit section
5. Externally connected TEL OFF HOOK detection circuit
6. CI detection circuit
7. Signal/DTMF transmission level & receiving level
Fig. 5
3) Block description
1. Speech circuit section
• The receiver volume is an electronic volume type, this model is
switch in 2 steps.
2. Dial transmission section
• D.P. transmission: The CML relay is turned on and off for control in
the DP calling system. (Refer to the attached sheet.)
• DTM transmission: It is formed in the modem, and is output.
3. Speaker amplifier section
• The volume of the ringer sound/speaker sound is controlled with
3-bit signal of VOLA, VOLB and VOLC, and the sound switch is
controlled with BZ CONT.
4. Ringer circuit section
• The ringer sound is formed in the tone of 1-chip engine when CI
signal is detected. The amplifier circuit drives the speaker of the
main body.
5 – 8
SIGTX
SIGRX
MODEM
(R96V24)
SP AMP
4051
CI DETECTOR
HS DETECTOR
TEL LINE
EXT
+5V
+24
DG
CI
TEL MUTE
RHS
HOOK SW
HANDSET
SPEAKER
TELIN
TELOUT
RXIN
TXOUT
HS
CML
CONTROL PWBTEL/LIU PWB
VOL A
VOL B
VOL C
BZCONT
TXCONT
RXCONT
MONITOR
BZCONT
RCVOL
SP MUTE
TEL MUTE
CI
GAIN-C
CML
HS
4053
1
0
1
0
GAIN-C
TXCONT
0
1
1
0
10
0
1
FC200
H
L