So I fried a computer motherboard(oldish z97 board housing a 4790k) tonight at church while getting setup for our Tuesday night livestream. We're borrowing space in a fairly old church in a small town, so I suspect that the wiring might be on the questionable side, although we hadn't had any issues until now. This setup had been working fine for several weeks. We basically have an XR18 near the stage with some powered speakers providing monitors and FOH and at the back of the room is the aforementioned PC for running lyrics and, since the COVID pandemic, the livestream. The audio is provided via a 50ft USB extension cable connecting the PC to the XR18's USB interface port.
So tonight I had to hook the mixer back up and re-connect the FOH/monitors as I had used them over the weekend for a gig(PA is my personal rig, but it stays at the church and gets used for the weekly Tuesday night service). I had the mixer on while I was finishing getting it connected and my brother was on the PC getting it ready to go. When I went to plug in the USB cable(short A-B cable connected to the 50ft extension) to the mixer there was an arc and audible pop as soon as the metal on the USB connector touched the metal of the port on the mixer. Immediately the PC shut off and best I can tell the motherboard is fried; I don't have another machine handy to test the CPU. The power supply does turn on when jumpered and the mixer survived apparently unharmed.
Any thoughts on what happened and/or is going on with the electrical in there? Currently I don't know if the PC and mixer are on the same circuit, but I plan to do some investigating this weekend to find out. Is there anything I can test? I have a DMM and have done some household wiring.
Thanks in advance,
Tommy