USB power drop or bad cable. Solution: Use a powered USB hub. If still stuck, hard power cycle (unplug 30 sec) and restart the flashing process. Do NOT turn off during write.
Extract the archive and connect your printer to a computer via USB. Printer Toner Reset Firmware Fix Samsung Clx 3185.rar
No firmware flashing, no brick risk. Cons: Requires soldering or conductive glue on each cartridge. USB power drop or bad cable