Read Panasonic KX-TG2560B / KX-TG2560S Service Manual online
44
KX-TG2560B/KX-TG2560S
11. Parallel Connection Detection Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, a circuit that determines
whether a telephone connected in parallel is in use or not is needed. This circuit determines whether the telephone connected in
parallel is on hook or off hook by detecting changes in the T/R voltage.
Circuit Operation:
Parallel connection detection when on hook:
When on hook Q103 is ON, the voltage is monitored pin 40 of IC701. There is no parallel connection if the voltage is 1.65 V or
higher, while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when off hook:
When off hook Q103 is OFF, the voltage is monitored pin 40 of IC701; the presence/absence of a parallel connection is
determined when the voltage changes by 0.2 V or more.
Circuit Diagram
1
2
L101
C103
~
~
D101
C104
R102
R108
RLY
DCIN
USE-CTL
Q103
Q101
Q102
R124
R105
R104
R101
C112
L102
CN101
SA101
99
40
15
P101
R109
R103
IC701
DSP
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