The message "Sonos Arc HDMI 3 No Signal” sounds like it’s an HDMI-CEC issue.

I think Samsung call their version of the protocol "Anynet+". I would suggest powering off (not standby) the TV and all its connected devices for a minute. Unplug the ‘other’ connected devices too, leaving the Arc attached and then power on all. Check Anynet+ is enabled on the TV and that the audio-out is working and then connect the ‘other’ devices back to the other TV HDMI ports. 

If the problem re-occurs, then perhaps try switching off HDMI-CEC on the ‘other’ connected devices, or use a CEC-Less adapter as shown in this link:

https://www.amazon.com/Lindy-HDMI-Adapter-Female-41232/dp/B00DL48KVI

Thx Ken, yes, I have done all that & Anynet is enabled :( 

I haven’t heard about CEC.  I’ll research that & share your info with my surround sound installers.

Thx again!

Have you managed to get the TV/ARC back up and running now, or do you need help from the user-community here?

If it still isn’t working, I would suggest toggling off/on Anynet+ whilst you have just the ARC connected to the TV, just remove the devices from the other HDMI ports temporarily why you do that. Also ensure the sound-out is set to the TV’s HDMI-ARC port, rather than the internal TV speakers - again you can toggle between those TV settings too, to ensure the ARC port is set as the audio out.

Hope that helps.

As with any CEC potentially related issue, it’s always wise to both check for any updates to the TV, and then reboot the TV by unplugging it from the wall for two minutes. Sometimes a firmware update/refresh helps. And certainly doesn’t hurt. 

Ok, I toggled the on & off for anynet & my Sonos & Samsung are both updated.  Yes I did unplug TV from wall. I guess I’ll have to listen to TV audio until Monday when I can get Sonos support :(

Thx for all the suggestions!

Did you also toggle the TV sound-out between the internal TV speakers and the HDMI-ARC port and check the audio format is still set to Dolby Digital (preferred) or PCM (fallback codec). 

Is your HDMI cable rated for eARC?

I’m pretty sure my old ones aren’t so I ordered one to have it on hand when my ARC arrives off backorder.

I can’t find any detailed cable specifications in the Sonos documentation.

I hope this may help too, I copied the below from one of the Staff posts about the HDMI cables that Sonos use...

Any HDMI cable with HEAC support can handle eARC. Both the HDMI cable which comes with Beam and Arc have HEAC support.

Technically there are four kinds of cable :

• Regular HDMI
• High-Speed HDMI
• High-Speed HDMI with ethernet 
• Ultra-High-Speed

The cable that comes with the Beam/Arc is a High Speed one with ethernet, whereby the ethernet pins are used for eArc. Sometimes referred to as HDMI 1.4+

Came with my Beam? Arrrghhh.

Off to dig in the spares closet.

Yes, the cables that Sonos includes with their sound bars are appropriate to carry the necessary signal.

I think I have found the Beam cables, not sure as there are no markings on the cable, but the ends look like the pictures in the user’s manual.

I’ll tag them as Sonos Beam so I don’t confuse myself in the future.