Panasonic KX-TD612NE Service Manual page 13

transmitted to the ringing transformer through pin 7 of CN101.
3. AC cut off detection function:
AC power failure is detected by R31 - R36, R38, D31-34, C31 and
PC2. When AC power is on, pin 4 of PC4 is high. When AC power
is turned off, pin 4 of PC2 changes to low.
4. Battery back up function:
This back up battery adapter circuit has DC supply function, from
battery (+24V) to service unit and DC charge function from service
unit to battery (+24V). Charge current is 0.4A.
2.3.2. MAIN BOARD
1. CPU Block
13