iMac 2015 - Burn mark on back of screen - Potential DAC Issue

Fixing a 2015 iMac which will not power on.

From tearing it down I found a burn mark on the back of the screen which is just in front of the Cirrus (CS4208-CRZ BGA) on-board DAC. It has likely blown.

After chatting to the friend of a friend he has been running the iMac through his amp using the headphone port. He had a power outage/short during the week and the iMac hasn’t turned on since. This seems to be in line with the visible burn mark.

Diagnostic LED #1 is illuminated. When I hit the power button the hard drive is turning on but no other LED’s illuminate.

At this point I am thinking of replacing the logic board. Any other tests or things to look for before doing so?

Thanks in advance.