I'm able to flash an image using Rufus onto a USB and boot it up on a Wyse Z90. I have a screen and keyboard connected and can execute commands without any problem.
I then proceeded to flash the internal 4GB SSD with the same image using an Ubuntu Live system on USB. I can mount /dev/sda1 & /dev/sda2. The boot partition has the standard grub.cfg. The files on /dev/sda2 all look fine. In all it's a clone of the openWRT system I booted from the USB drive.
When I try to boot from SSD the screen shows "Grub..." briefly then ... nothing. Prior to this the SSD hosted a minimal Ubuntu server so I'm sure the SSD is OK.
I've poked around for several hours now. If any of you kind folks could offer some suggestions I'd be very grateful.