There is a bug in the SD flashing routine in the firmware that can brick the ZX-Uno. Firmwares v0.48 and newer have fixed the bug. At the moment only there are reported 2 bricks, but to avoid more, these are the instructions for a safer upgrade:
Steps to upgrade through ESXDOS (use attached files):
- Use a SD with working ESX-DOS 0.8.6 beta4 installed
- Copy FLASH.ZX1 on the root dir, UPGRADE on the BIN dir into the SD
- Boot with "Rooted 48K"
- Write .UPGRADE in the command line (remember initial dot)
- Wait the progress. After finish reboot your ZX-Uno
If all is ok you'll have v0.50 BIOS. Next upgrades can be done using BIOS because they are safe.