Rock-4C+ HDMI stopped working

I’ve had it for a couple of months, working fine.
This afternoon, the HDMI just stopped working.

It’s as if the Desktop went to sleep, but now can’t see any wakeup signals (mouse movement, KB) - even though the mouse & KB are clearly working.

I can still login via SSH.

Full details here:

Is it broken? What other tests can I do?

Dumb question; Did you try the other hdmi connection ? I have had these flip which port is active.

Yes - see the linked post.

Smarter people than me may have better suggestions, but I would use xrandr to send screen through the other port as long as you have an ssh connection.

I had never tried the other port before - should it “just work”? Should I be seeing something on it anyhow?

But none of this answers the primary question of why the 4K port has stopped working - and what to do about it.

As in this: ?

More specifically: ?

Update (from the DesignSpark thread):

It had been going through an HDMI switch. Removing the switch and connecting direct to the monitor, it works again!

So that leaves 2 questions:

  1. How come it was working fine for a couple of months, and then just stopped?

  2. How to diagnose what’s going wrong when using the switch?

Note that other devices (a Windows PC; a Raspberry Pi) still work fine through the switch.

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

maybe more: