Make sure your device is fully charged and turned off.
Websites like SamMobile or Samsung Semiconductor often host firmware for various models. samsung gt-c3520 flash file and tool
| Problem | Solution | | :--- | :--- | | WinDup doesn't see phone | Install BCM driver manually from WinDup folder. Use Windows 7. | | Error: "Bootloader mismatch" | Your firmware's bootloader is different. Find a full package including Apps_boot.DNF . | | Error: "Invalid DNF file" | The file is corrupted or for another chipset (e.g., C3520 uses BCM2133, not BCM2153). | | Phone stuck in bootloop after flash | You flashed wrong Reed.DNF . Flash again Reed file. | Make sure your device is fully charged and turned off