Panasonic KX-TMC40JX-W, Service Manual

Page: 34 / 63

9.9. 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 Q101 is ON, the voltage is monitored pin 35 of IC201. 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 Q101 is OFF, the voltage is monitored pin 35 of IC201; the presence/absence of a
parallel connection is determined when the voltage changes by 0.2 V or more.