Mac mini died overnight, will not power up

I was having trouble with my late 2012 Mac Mini last month. After troubleshooting, I found that one stick of RAM was failing. I ordered two new sticks and also replaced the HDD with a SSD (thanks ifixit tutorial). Restored everything from Time Machine backup, and the Mini has been chugging along beautifully.

Fast forward to two nights ago, and it just flat out dies. No power at all, completely inaccessible. SMC reset, PRAM reset, etc. do nothing. Powered off all night and plugged in to try these things again, but no luck. I’ve taken it apart today and pulled the power supply as my first hardware troubleshooting step (update below to show the power supply is fine). I cannot find a proper pinout for the Late 2012 power supply harness, but the outside pins are showing 11.9VDC across them, which makes me think it’s operable. However, I don’t know the rest of the pins and desired voltages, and can’t find it anywhere online.

I have another Mini available, but it’s operating as a server and I hesitate to take it down for testing. It’s probably my best way forward, but I figured I’d ask if anyone had other troubleshooting steps/logic board testing ideas before I do so.

Update (02/16/2019)

I went ahead and pulled the other Mini, and the power supply is able to boot that machine. So I'm back to looking at the logic board. I hear a "tick" sound repeating, which is coming from the back portion of the logic board (the part that wraps behind the HDD space). Thoughts on that?

Update 2 (02/16/2019)

The repetitive ticking sound appears to be coming from the communication board. If I remove the ribbon cable from that comm board, it no longer makes the ticking noise (but still doesn’t boot). I have everything removed and have only the logic board and power supply connected. I’m beginning to think I’ll need to replace this logic board, but I do want that to be the last resort if possible.