KX-TDA0103X, KX-TDA0103XJ, KX-TDA0104X, KX-TDA0104XJ, ETX1KM753MB, ETX1KM752MB - Panasonic PBX Service Manual (repair manual). Page 13

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This section generates the Alarm signal such as AC ALM, DC ALM and FAN ALM

1. AC ALM Signal Output

The detection of AC is done on the Primary and the information is transmitted to the secondary side via PC001. 
AC ALM is generated by the IC133 by monitoring the condition of the transistor side of PC001.
IC133 : Voltage monitoring IC with delay.
Q134 : Open Collector Output buffer transistor for AC ALM

2. DC ALM Signal Output

The detection of each of the output voltage of 15VP, 30V and 41V. 
DC ALM is sent out when any of the output voltages drop below the pre-set value or when AC ALM is activated.
However, when a working Battery is connected to CN604 DC ALM is not sent out during the period AC ALM is activated while 
the DC output voltages are within the pre-set value.
SW601: Battery Backup On/Off control
Q165, D135, Q133: Negate the sending out of DC ALM during AC fail and Battery backup is activated.
IC131, IC132 : Comparator IC for detecting the status of each output.
Q130: Open Collector output buffer transistor for DC ALM

3. FAN ALM

Send an alarm signal to the PBX system when the Fan stop operation.
Fan Stop signal is generated by the fan
Q202 : open Collector Output buffer transistor for FAN ALM