Greetings, first post (because I'm desperate), not an audiophile.
I have the Onkyo HT-R500 receiver. The in-the-box SKW-100 subwoofer goes into standby when playing DVDs. The sub works great (and pounds!) w/ TV and radio. It sems to be an intermittent problem, mostly in DVD mode. When I start a DVD, the sub is on for a few minutes, then the sub goes into standby. I can cycle the sub power and get it back, but then it goes into standby again later. I suspect the the signal is to too low, but I'm an AV dunce.
This seems related to the volume level on the receiver. While set to Video1 (i.e. the TV), the volume setting is around 80, and I use the TV volume setting to control volume from there, sub seems fine like this. When I switch to DVD, I set the receiver volume setting to between 50 and 60 or so for typical DVD viewing (and listening). I know some of you crank it, but over 60 is pretty loud for most DVDs.
I'm past warranty, looking for help. Thanks in advance.
Check your receiver setup and see if the "LFE" channel is turned off for surround modes. I think on Onkyo its under the Setup and Subwoofer on/off.
This would have the effect that you describe since turning the LFE or x.1 channel off would only be noticeable during DVD or other surround content. I believe the subwoofer is active in stereo mode just as an additional audio output for low frequency signals.