(If available, include exact BootROM output lines, timestamps, and UART baud/settings here.)

: Check that your USB-to-UART converter is set to the correct voltage (typically 3.3V rather than 5V) to match the STB's logic levels. Driver & Software Configuration :

: The most frequent culprit. This includes loose USB cables, faulty USB ports, or poor solder joints on the UART pins if you are using a USB-to-TTL adapter.

: On some unbrickable devices, you must manually short the eMMC "CLK" or "Data" pins to GND momentarily during power-up to prevent the device from loading corrupted internal firmware and force it into MaskROM mode. 3. Update Drivers and Software