Panasonic KX-TG3411BXH Service Manual page 16

KX-TG3411BX/KX-TG3412BX/KX-TG3419BX/KX-TGA341BX
4.5.5. Parallel Connection Detect Circuit/Auto Disconnect Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. 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, the voltage is monitored at pin 27 of IC501. There is no parallel connection if the voltage is
0.54 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, the voltage is monitored at pin 13 of IC501; the presence/absence of a parallel connection is determined by
detecting the voltage changes.
If status is Hold, BBIC disconnects the line after detecting parallel connection is off hook.
Pin 13 of IC501
PARADET
R151
R121
R152
C152
Pin 27 of IC501
ADC0
HOOK
Pin 15 of IC501
Q141
Q161
Q142
R122
16
C101
D101
L101
3 2
4 1
C102 L102
L1T
L1R
TEL JACK
P101