FO-2970MU
[3] 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 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.
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 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 PC1 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.
Fig. 23
H
L
HS DETECTOR
CML
CI DETECTOR
0:LINE
1:BZ
SPEAKER
LINE
+5VA
+24VA
DG
BZCONT
TELOUT
TEL IN
EXT.
RX
RXIN
TXOUT
CML
HS
0:CID
CONTROL PWB
LIU PWB
SIGTX
SIXGRX
1:RX
0:MID
1:HIGH
TEL MUTE
(H:MUTE)
IC15 G.A
LR38784A
SP MUTE
(H:MUTE)
BZOUT
BZCONT
RCVOL
VOL C
VOL B
VOL A
SP MUTE
TEL MUTE
CI
RHS
GAIN-C
CML
HS
IC5 SH2
(7041)
HOOK-SW PWB
TX
GAIN -C
CI
MIC MUTE
IC8
MODEM(FM336)
SPKR
5 – 21
Summary of Contents for FO-2970M
Page 70: ...FO 2970MU 6 10 Control PWB parts layout Top side ...
Page 71: ...FO 2970MU Control PWB parts layout Bottom side 6 11 ...
Page 73: ...FO 2970MU 6 13 TEL LIU and Hook SW PWB parts layout Top side ...
Page 74: ...FO 2970MU 6 14 TEL LIU and Hook SW PWB parts layout Bottom side ...