ARC not working with Fire TV after 'something changed'

[martens]

I have Apple TV 4K (latest generation) connected to my Fire TV's HDMI/ARC port (HDMI4). It's connected with a pair of HomePods (2nd generation). A BluRay player is connected to a different port (HDMI3).

In the past I have been able to have the BluRay audio play through the HomePods (then 1st generation HomePods). But AppleTV says 'ARC is not supported on this input, make sure CEC is enabled' and I have to use the TV speakers instead. I've checked FireTV, ARC is enabled and the cable plugged into HDMI4 actually goes to the Apple TV (eliminating possibility I mixed them up). I have had ATV run a check on the HDMI input and passed.

FireTV firmware has not changed since I got it and updated at that time. It's never been able to connect to the internet since then. I did swap in the newer HomePods (which shouldn't affect any of this), and Apple TV has had at least a couple of updates since it worked. So it seems some tvOS update broke it.

Any other ideas?

 

[-Gonzo-]

HDMI Reset - basically remove all devices from mains power then remove the HDMI cables.
Leave for around 5 minutes then connect to mains power again.
Power on devices and put into standby then reconnect the HDMI cables and then power on the devices one by one starting with the tv.

 

[martens]

Thanks, that worked! We've been having frequent power outages here (replacing all the utilities poles), I guess that could have messed it up.