I just downloaded http://mirror.centos.org/altarch/7/isos/aarch64/CentOS-7-aarch64.img.xz uncompressed it. Read the readme.txt
dd if=CentOS-7-aarch64.img of=/dev/sdd bs=2M conv=fsync && sync;
put the new SD card in the PI3 and connected power I got nothing. my SD card is 32G.
I tried the 32bit image and that booted and ran fine. So my hardware is Ok.
Thoughts?
Jerry