I tried that again, and still failed. However, I remembered reading about bad SD cards - so I switched to a USB stick - and it worked!!!
My apologies to both of you - I should have done that a long time ago. Anyway, this is where I am:
Armbian_5.37_S9xxx_Ubuntu_xenial_3.14.29_mate_20171226.img with NO dtb loaded
can boot into GUI desktop
sound works
no wifi, can't test ethernet (router is too far away) - I only want wifi
TV is set to overscan, and I can't adjust it - so part of my display is cut off - I don't know how to fix that in Linux (if at all possible)
I appreciate the help you've given me so far ... but now I don't know what to do to have a usable system.
My knowledge of Linux commands is VERY limited, but any tips you can offer would be greatly appreciated.
Oh - if I need to load a DTB (for wifi, etc), can I just copy it to the USB stick and reboot, or do I need to do something different?
Thanks in advance!