Rock-4C+ HDMI stopped working

[awneil]

Somebody else having trouble with the HDMI output from a Rock Pi 4:

Force HDMI output on RockPi4

Hi, I’m working with a RockPi4 using DietPi. Now I’m facing an issue with a projector which doesn’t get recognized at the startup and the only way I found it to be tricked is starting up with another screen and then switching plugs. I’ve just purchased one of those HDMI plugs that might solve it but, in the meantime and cause I may need it for other purposes what I’ve seen is the “soft” solution which I’ve seen that in other SBCs is as simple as adding “hdmi_force_hotplug=1” in the config.txt. …

maybe more:

https://forum.radxa.com/t/rock-pi-4c-plus-defective