| Error Message / Symptom | Underlying Cause | |-------------------------|------------------| | Device not found | Driver not installed, device in wrong mode (normal boot vs. download) | | Download failed – timeout | Windows USB selective suspend, poor cable, or unstable COM port | | IMEI write failed – NAK | NV region locked; need to unlock using AT+SPNVM command first | | Checksum error | Tool version mismatch with firmware version on SC7715 | | Port open error | Another application (e.g., modemu, SPD Upgrade Tool) holds COM port |
: Ensure you have the correct Spreadtrum USB drivers installed on your PC. Launch Tool sc7715 imei tool download fixed
