I have an H50-labeled tv box with a different board (T98-3318-V2.3) but with exactly the same problem - no HDMI even though all the software debug traces show that everything video-related gets called and works.
I first tried to make it work 5 years ago and failed and a few months ago I revisited it just to see if I can make it work now in the age of AI.
I made a really deep dive into reverse engineering it. I rooted the original Android firmware and dumped anything I could, extracted and analyzed with Ghidra the vendor u-boot and kernel (wasn't particularly helpful) and finally managed to execute the u-boot binary in Renode by emulating a lot of hardware stuff with code or by simply replacing functions with successful returns all the way to the point of u-boot displaying the splash screen and with various hooks and warnings about peripheral accesses I collected a comprehensive trace of everything that u-boot was doing, and in that trace, the AI noticed a certain GPIO access and suggested replacing this
vcc-host-vbus {
compatible = "regulator-fixed";
enable-active-high;
gpio = <0x74 0x00 0x00>;
pinctrl-names = "default";
pinctrl-0 = <0x76>;
regulator-name = "vcc_host_vbus";
regulator-always-on;
regulator-min-microvolt = <0x4c4b40>;
regulator-max-microvolt = <0x4c4b40>;
vin-supply = <0x77>;
phandle = <0x100>;
};
with this
vcc-display-en {
compatible = "regulator-fixed";
gpio = <0x74 0x00 0x01>;
pinctrl-names = "default";
pinctrl-0 = <0x76>;
regulator-name = "vcc_display_en";
regulator-always-on;
regulator-boot-on;
regulator-min-microvolt = <0x4c4b40>;
regulator-max-microvolt = <0x4c4b40>;
vin-supply = <0x77>;
phandle = <0x100>;
};
in the standard rk3318-box.dts which made HDMI work.
