Panasonic KX-TG2448BXF, Service Manual

Page: 55 / 98

13.6. Parallel Connection Detect 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 Q136 is ON, the voltage is monitored pin 35 of IC501. 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 Q136 is OFF, the voltage is monitored pin 35 of IC501; the presence/absence of a parallel connection is
determined when the voltage changes by 0.2 V or more.
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KX-TG2448BXF / KX-TG2448B XS / KX-TGA254BXF / KX-TGA254BXS