Ac Alarm Circuit And Dc Alarm Circuit - Panasonic KX-NS700 Service Manual

1.5.

AC Alarm Circuit and DC Alarm Circuit

Added into the Original Service Manual as section 4.9.
This section describes the operation of the circuit that sends the AC alarm/DC alarm signal.
1) AC alarm circuit
When the AC Detection Circuit (described in section 1.2. (5)) detects AC input as "Yes", the Secondary side transistor of U1
turns ON. This action turns Q23 ON and then a LOW signal is sent to AC alarm output.
However, if the AC input is detected as "No", the Secondary side transistor of U1 turns OFF. This action turns Q23 OFF and
then AC alarm sending output becomes OPEN. (Open collector output)
Q18 functions as same as Q23 and the output of Q23 is used for DC ALM control.
2) DC Alarm Signal Sending Circuit
When 41V is output normally, shunt regurator U8 in the output voltage detection circuit turns ON and Q26 turns OFF. Q21 also
turns on and then DC alarm sending output becomes LOW.
When 41V output becomes abnormal, shunt regurator U8 turns OFF and Q26 turns ON, Q21 also turns OFF and DC alarm
sending output becomes OPEN. (Open collector output)
Q17 and Q25 function for the hysterysis of DC ALM detect/undetect voltage.
If AC alarm is detected, Q24 turns ON and Q21 tourns OFF (DCALM Low  Open) with some delay.
5