I published my Vontar H618 bring-up patch set here:
https://github.com/aco-art/vontar-h618-armbian-patche
It includes the Armbian userpatches, U-Boot/kernel changes, and diagnostics tools I used for this box. Tested on my 4 GiB DDR3 Vontar H618 unit and shared in case it helps with similar H618/H616-class TV boxes.
On my tested unit, Wi-Fi, Bluetooth, LAN, HDMI output, and the basic GPU/display path are working with this baseline.