My remote controller is smart in that it knows whether the tv is “on” or “off”. When tv is thought to be off, the volume control doesn’t work. Could this be your issue too?

Hmm. Could be but it should be able to override it? Should be communicating with playbar when tv is off.

 Hmm.

This depends: if the remote control itself is bluetooth and the TV transmits the ir signals, it won't work when the TV is off.

Interesting. So the playbar can't register Samsung q70t tv remote when tv is off.. that sucks.. 

It’s more of a case of “if the remote isn’t sending an IR signal, the PLAYBAR can’t read it”. It’s not the Sonos that’s failing to read the signal, it’s the remote failing to send the signal.

The PLAYBAR has no idea (essentially) whether or not the TV is on. The PLAYBAR is always “on” or ready to be “woken up” by an input from either wifi in the case of music, or through the optical port, in the case of a TV or other optical source. 

If your remote links to the TV using a Bluetooth connection, you may find there is a way to switch the TV to use a universal IR remote and/or be able to purchase an IR remote as an accessory - but in some cases users may opt to program their connected cable/STB box remote instead to control the Playbar volume with the TV either ‘on’ or ‘off’ and let the cable box connect to the TV over HDMI and use its built-in CEC feature to adjust/mute the TV audio.  

I'm using the Samsung one remote without an stb box.

The tv remote works when tv is on. But once the tv is off, it doesn't control volume at all ..

But is it the remote that controls the Playbar by ir, or the TV sending out the ir signals, while itself being commanded by bluetooth remote)?

That is how it works with my settopbox and my QE65Q90: the TV is controlled by the bluetooth remote, but the TV (Connectbox in my case) sends out ir commands to the settopbox.

In which case the TV does nit send anything when it’s off….

Dang that makes sense. I couldn't find the answer to that question.. but probably does. So remote doesn't work when tv is off. Ouch 

Well, the remote works. There’s just no middle man from bluetooth to ir…. 

Try this: turn the TV on with the remote but block the signal from the remote, so that the TV stays off and the Playbar is still playing a music source. Can the remote control operate the music volume now?

Played music. Closed my hand around Samsung one remote.. My tv switched on.. music still playing.. pressed power button again. Tv switched off. 

(Oddly enough: It is working but seems to stop .. seems like it works for a few seconds after TV turns off)

That’s not quite what I suggested. 
 

Do you have TV Autoplay turned on or off?

Hi. Yes. I usually have it on. (Maybe i misunderstood your suggestion. How do i block the signal of remote?)

Well, the tv won’t turn on if you successfully block the signal, will it? Put something over the emitter to block/absorb the signal, or go somewhere out of range so that the tv doesn’t receive the “turn on” command. Then, the Playbar will still be playing music and you can go back into range and see if the volume control works. 

If the remote is ir. I suspect it is bluetooth, though.