Sure shock ss 2000 electric fence controller

Unit works on hv side, problem is on alarm circuit, when fence ok light is on and fault light is off, siren output is on and relay output contact is closed. Will not reset and only switches when monitor switch is in off position. Board looks ok so i am suspecting faulty ic or transistor, any help would be greatly appreciated.

I remember some fence controller discussion where there was a "homemade" optocoupler and that failed. By home made, it was a photo--transistor and an IR LED separated by a large distance to probably get lots of isolation, I don;t remember the model being discussed.