Fire-Lite MS-4 Fried NAC

Hi everyone. I have a Fire-Lite MS-4 circuit board on which NAC 1 has been fried. I’m not exactly sure what I did to it although it’s possible I back-fed voltage into the circuit. Anyway, what happens when the panel is on is that it displays a “NAC fault” which can be acknowledged although it will resound after a few days or so. I have checked the voltages on the circuit with a multimeter, when normal, the polarity of NAC 2 is reversed and reading ~2 volts, as it should. NAC 1 however is not reversed and always reads about 1.5 - 3 volts regardless of the panel being normal or in alarm (when it should be outputting 24 volts). The circuit board has since been removed from service but what would it take to rectify the problem on this board? I have a little experience in soldering and the way I see it, I can only fix it. I can’t use it anymore and it’s not worth what I paid to have it professionally repaired, especially since I am now using a Silent Knight 5808 for my hobby setup. So if anyone knows a way to repair these kinds of things, please let me know. Once again, I am not concerned with accidentally damaging it further since I do not plan on using it but I would consider it a success if I could actually fix it.