APM power module starts ok but then goes o/c?

Wonder if anyone has encountered this. I have a new pixhawk and new APM power module. I plug in 3s lipo and connect to pc to configure controller for flight. Working away for several minutes and suddenly the pixhawk smokes around the power plug and the board fries apparently as now it just lights white solid light. Anyway I check the APM and its putting the whole 14v through. Solved apparently as faulty APM so I complain to manufacturer. I want to take an image of the fault so next day get camera and put voltmeter across and APM power module is putting out 5 volts perfect. I am going crazy now what happened and then wonder is it that the APm faults when it gets hot? Ie after a few minutes but is ok when tested. Has anyone seen anything like this or confirm my logic as otherwise it don’t make sense.

How did you fix this? Did you get a new one or did you manage to troubleshoot?