I have recently encountered the same issue. My Minix U9-H starts and I see the Minix logo, green android bot and HDMI in the bottom right corner but after a few seconds, although the blue light remains lit, my 55 inch LG 4K TV says No Signal. This Minix box has been working with the original firmware for several years apart from the odd times when it froze and the power cable has to be disconnected. I cannot update it's firmware as I only have access to a Chromebook and a Windows 10 S laptop. Is it really just some sort of display issue?