Unknown error tones, burned pixhawk for no reason

I am diagnosing a friend’s drone. It appears very dead, but we are trying to identify why. They said they had powered it up at one point to just check that everything was working. It had flown before many times and there was no reason to suspect anything was wrong. A current sensor had been replaced recently, but it functioned correctly too. The old one failed from a factory cold solder joint on the shunt.

When the pixhawk powers up, it plays what sounds like the first half of the boot beeps, then suddenly it plays a series of tones that I can’t recognize, and then it plays the boot failed tones. I am told there was also a burning smell from the pixhawk. Later inspection shows this to be the largest IC on the bottom of the board, I assume the main controller.

We have measured the voltages on all inputs and they appear to be completely normal. This failure came unexpectedly with no real changes to the system, it just sort of happened. We are unsure as to what could cause this, and its an expensive glitch to just fry pixhawks.

This is what it plays. It’s surely dead, but why?