Circuit Description Of Tel/Liu Pwb - Sharp FO-475TH Service Manual

[3] Circuit description of TEL/LIU PWB

(1) TEL/LIU block operational description
1) Block diagram
TEL LINE
HS DETECTOR
EXT
HANDSET
HOOK SW
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
TEL/LIU PWB
H
L
CI DETECTOR
TELIN
TELOUT
SP AMP
SPEAKER
CONTROL PWB
HS
CML
GAIN-C
TXOUT
0
RXIN 1
1
0
VOL A
VOL B
VOL C
4051
TEL MUTE
CI
RHS
+5V
+24
DG
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
TXCONT
SIGTX
1
MODEM
0
4053 (R96V24)
1
SIGRX
0
1 0
BZCONT
0
1
TXCONT
RXCONT
MONITOR
BZCONT
FC200
RCVOL
SP MUTE
TEL MUTE
CI
UX-258TH
FO-475TH
GAIN-C
CML
HS