Panasonic KX-T2388 Service Manual And Technical Manual page 24

KX-T2388
ME CPC (CALLING PARTY CONTROL) DETECTOR CIRCUIT
Function:
The CPC DETECTOR complements the units shut off, in the ANSWER mode, after the caller hangs up. At this times,
the CPC DETECTOR takes over. The CPC DETECTOR senses the temporary disconnection the telephone line which
occurs after the caller hangs up.
Circuit Operation:
When the unit seizes a line, current will flow through D5~D8, Q101, R10, Q3 and R13. Also a result, voltage will be
applied across R13 causing current to flow to the base of Q4 via R14. As a result, [C1 pin 35 will go LOW. If then the line
is momentarily cut, line current will cease to flow, and voltage will no longer be applied across R13, thus Q4 will turn
OFF, and !IC1 pin 35 will go High, hence this condition will be detected.
Circuit Diagram
R10 DS
IC1
less than 5 ms less than 350 ms
Mi VOX CIRCUIT
Function:
The vox circuit is designed to detect cyclic signals is which the signal is ON for 100 msec. to 1 sec, continuous sounds
and no-sound at all.
After detection, the CPU issues an instruction that makes VOX operation possible.
This means that when a telephone call has ended, the phone is reset and is ready to receive the next call.
Circuit Operation:
A signal output from terminal pin 16 of IC2 passes through C26, R48, then it is amplified and rectified by C29, R51, D18
and D19.Then it is inputted to the comparator which consists pin 13 of IC2 . The output from pin 12 of IC2 is inputted to pin
14 of CPU(IC1). When sound is present, the output at pin 12 of IC2 becomes a low level, while with no-sound its output
becomes a high level.
Circuit Diagram ste See page 24.