I writ:
“The latest kernel kernel-3.10.0.229.1.2.el7.x86_64 appears not to like our Supermicro X9SBAA-F board. It fails on boot with the last message before panic being apic_timer_interupt ….”

It turned out that only one X9SBAA box was affected.

Deleting and reinstalling the kernel did not fix the issue. The problem turned out to be the old “initrd” issue in grub.conf. We have seen this from time to time on updates in the past. The line:
initrd /initramfs-3.10.0-229.1.2.el7.x86_64.img was missing from grub.conf. When manually inserted, the new kernel worked swimmingly. I suspect that this is related to updating grub either immediately before or after a new kernel is installed. It’s just enough of an annoyance that someone with spare time on their hands might want to look in it.