Read Panasonic KX-FP320E / KX-FM330E Service Manual Simplified online
16
(Model KX-FP320E/KX-FM330E)
KX-FP320E/KX-FM330E
6.9.6. SIDE TONE CIRCUIT (Change from original page 174)
1. Function
A sidetone is the returning of the TX signal to the RX signal. The sidetone circuit uses a bridge circuit to attenuate the
sidetone. Howling may occur if the attenuation of the sidetone is inadequate.
2. Circuit Operation
The TX signal is output to the circuit along the route from the IC10-1pin
→
C37
→
R58
→
R57
→
T1
→
TEL LINE. However,
if balance is lost in the bridge as shown below, a voltage occurs between the IC10-5 pin and 6 pin and a sidetone results.
Because the balance cannot be maintained completely at all frequencies in the audio range, some sidetones always occur.
C159
Circuit Diagram
Z
Line
T1
1:1
Z
BAL
R71
R66
C48
R62
R61
C159
Z
A
IC10
1
2
3
3
R73
C53
IC10 C44 R59
5
6
C47 R65
RX Signal
7
Side Tone
TX Signal
C160
C38
C37
R58
R57
Z
B
_
+
_
+
IC5(59)
LINEIN
LINEIN
IC5(63) LINEOUT
Conditions for bridge balance
Z
A
×
Z
BAL
=Z
B
×
Z
LINE
↓
(Z
A
= Z
B
)
Z
BAL
= Z
LINE
Z
LINE
: Tel line blockage
6.9.7. REMOTE FAX ACTIVATION CIRCUIT
1. Function
Another telephone connected to same line activates the unit to the FAX mode by using a DTMF signal.
2. Circuit Operation
TEL Line
→
T2
→
C115
→
R154
→
IC5 (61
→
67)
→
R167
→
C134
→
IC2 (10
→
11)
→
C68
→
CN7 (9)
→
{CN501 (9)
→
C701
→
IC801(3
→
4)
→
C943
→
J604
→
C603
→
IC5(60)}
{ }........Digital board
6.9.8. AUTO DISCONNECT CIRCUIT (Addition)
(1) Function
This circuit is used to detect that the telephone connected in parallel to the same line is OFF-hook while the unit picks up the
line. If this detection circuit is activated when TAM is being delivered, the delivery stops and the circuit is automatically
released.
(2) Circuit Operation
If the line is picked up, C19 is charged by following the path shown below.
D6 (+)
→
Q3
→
R24
→
D12
→
C19
When the electric potential difference between the base and emitter of Q4 becomes less than about 0.3V, Q4 and Q6 and
PC5 turn off, then the IC5 pin 5 becomes a high level.
In this condition, if a telephone connected in parallel goes into OFF-hook status, the base of Q4 becomes low.
On the other hand, the emitter of Q4 goes down because the capacitor (C19) is charged. Q4 turns on when the electric
potential difference between the base and emitter of Q4 becomes more than 0.6 V while being charged.
When Q4 turns on, Q6 and PC5 also turn on, then the IC5 pin 5 becomes a low level.
Circuit Diagram
~
~
+
+
+
–
–
–
R29
IC5
C23
PC5
Q6
R29
R30
R31
Q4 D15
R28
R26
D13
D12
D11
C19
C17
R24
Q3
R17
D6
5
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