New issues, related to the snapshot. It may be obvious to the old users and perhaps it's already documented in this forum somewhere, but I can't read Russian. Maybe this little information will help someone else later.
Taking the snapshot using the NMI button only works when using the EVO ProfROM.
I also tried TRDOS ("BETA1024") from GLUK Service. CAT says "No disk" on the first or first two attempts but eventually sees the files on the physical disk. After the files are listed, the GOTO command happily loads them using the GOTO command. I also found LIST says "Out of memory" a lot of times, especially if the CAT command failed first, it looks like a bug to me. Pressing the NMI button brings up the same interface that the EVO Service has, a simplistic menu and the register contents and not the feature-packed monitor of the ProfROM mode.
I was able to create an empty TRD disk image under Linux, mount it in the EVO Service mode and copy all the files to from the physical disk to the disk image, so it's a good bridge between the floppy, the SD card and sending the image on the Internet or archiving and restoring. But loading the snapshot doesn't work at all in this mode, neither from the physical disk nor from a disk image. I tried both starting TRDOS from the EVO Service menu and by RANDOMIZE USR 15616 from 48K mode. Neither combination worked in the EVO Service mode.
Mounting disk images from SD card only works in the EVO Service mode, they are not persistent when rebooting in a different mode.
Is there a comprehensive documentation about the ZX EVO in English? Like what can be done in the 3 standard modes (EVO Service, GLUK Service and EVO ProfROM), with all the features and differences (and bugs) like the ones I just discovered.
Anyway, it's a versatile little thing, it is really 3 machines in one and can also be extended with a custom set of ROMs, so it's possibly 4-in-1.