Panasonic KX-F1200 Service Manual And Technical Manual page 126

KX-F1200 i
6-5. AUTO DISCONNECT CIRCUIT
1) Function:
This circuit is used to detect the fact that another telephone connected to the same line is OFF-Hook while the unit is in the
time of TAM'S answering operation or line hold operation.
2) Circuit Operation: (ex. Line1)
Tip (Ring) --, REC1 _ Q1 --, C8 --* D1 --, R10 --, Q2 ---, PC3.
During this interval C8 charges and the base of Q2 becomes high, and PC3 pin(2) becomes low, causing PC3 to go ON.
If a parallel-connected telephone or external telephone is put into an OFF-HOOK status,, charge ceases to flow C8 and the
base of Q2 becomes low, causing PC3 to go OFF.
When a line is connected, Q2 and PC3 go ON, causing pin 99 of IC1 to go low. When the line is disconnected, Q2 and PC3
go off, causing pin 99 of IC1 to go high.
6-6. LINE AMPLIFIER AND SIDE TONE CIRCUIT
1) Circuit Operation (ex. Line1)
The reception signal received as output from the line transformer T1 is given as input to R21, C21 to IC14 pin (2), and it is in-
putted to the reception system at an amplifier gain 12.5dB from pin 1 of IC14.
The transmission signal given as input to IC14 pin(6) is amplified to about 20dB, it is outputted form pin 7 of IC14 and it is
transmitted to T1 via R20. Without R27, R25, C23, the transmission signal would return completely to the reception amplifier
via R21. Here, the signal output from IC14 pin(7) passes through R27, R23, IC23 and enters the amplifier IC14 pin(3), a sig-
nal with the reverse phase of the transmission signal is formed at IC14 pin(l), and this is used to cancel the return part of the
transmission signal. This is the side tone circuit.
Transmission Signal: IC7 (2) --* R30 _ C29 _ IC14
(FAX)
[
Transmission Signal: IC3 (15) _ R29 --, 028 -J
(Voice)
(6)(7) T R20 _ _ Telephone Line
R271 '1
R25
(Side Tone)
C23
1
IC14 (3)(1)
l
Reception Signal: Telephone Line --, T1 _v R21 --, C21 --, IC14(2)(1)--r-_R189 (FAX Signal)
L'-R173 (Voice Signal)
6-7. MULTIPLEXER (IC7)
This multiplexer is used for switching and selecting the transmission and reception systemof the FAX circuit(modem).
Multiplexer (IC7)
Control
Switch Mode
A (,Pin 10)=Low
B (Pin 9)=Low
A=High Pin 5-3
A=Low Pin '2-3
B=High Pin 15-13
A=High Pin 4-3
B=High Pin 11-13
Pin 1-3
ON
Pin 12-13
ON
ON
ON
A: ICl Pin 35
B: IC1 Pin 36
Operation
Line1
FAX Reception
Eine2
FAX Reception
L\nel
FAX Transmission
Line2
FAX Transmission
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