| Error | Likely Cause | Fix | |-------|--------------|-----| | Sync failed | Wrong COM port / baud rate / cable | Check connections; try 38400 baud | | Flash write error | Wrong firmware or chipset mismatch | Get correct firmware (board version matters) | | Timeout | STB not entering upgrade mode | Retry power-on timing; disable any other serial software | | File format not supported | Wrong file type | Convert or rename to .abs or .bin (if supported) | | Cannot open COMx | Port in use or driver missing | Close other apps; reinstall USB-serial drivers |

Connect the USB cable between your PC and the STB’s USB port. Do not power on the box yet.