HKC panel board damaged

mattym

Somehow while changing the battery in my HKC alarm panel i damaged the circuit board. The keypads and pir's were not powered up when i came home from work so i checked the battery in the panel and it was dead. Today i tried to change the battery but as soon as i connected it a component labelled RJ on the top of the pcb started smoking and is clearly damaged. Anyone have any idea whats up? The alarm is up and running over 4 years without a problem but just came home to a dead system out of the blue...