busted Mac Pro (late 2013)

My guess is that I’ve broken something so here’s my sob story. I’ve been away from Macs for a while so hopefully I haven’t exhausted all the possibilities.

I bought a Mac Pro (late 2013) 6-core, 16Gb RAM, 512Gb SSD, fresh Monterey install. 99% sure it was running OK.

Upgraded the RAM to 64Gb (OWC). All good.

2Tb SSD (OWC) + fresh Monterey install. All good.

Upgraded the processor to 12-core (ES-2697V2; Amazon). Not good.

At this point I have ‘kernal_task’ using about 90% CPU (2000% in activity monitor) and as you would expect, the machine is a slug. Bought 2 of the 12-core CPUs so I swapped in the other one. Same thing. Back to the 6-core, same thing.

Installed HWMonitor and nothing is over 50C. The only numbers that look weird are “zone 1” and “zone 2” power consumption reporting 1500+ watts. Unsure if these sensors are real or if I’ve broken them. CPU reporting 20 watts total.

Apple Hardware test reports no issues found.

command-option-P-R on boot didn’t fix the issue. After the first chime the machine shuts down rather than reboots. Normal?

So apart from relegating the trashcan to the display shelf I’d be happy to hear any suggestions to try and fix the issue.

Thanks in advance,

Scott.