It really depends on the set-top box and the programs you're playing. Some boxes will turn off the component if its senses a single over the HDMI connection. Some boxes won't turn on component output if it sense the HDMI port is plugged but there's no signal. Some boxes will shut off the component connection if it sense a HDMI connected device and a DRM program is playing.
Bascially what I'm trying to say there's no standard in how HDMI and component outputs work together across manufacturers. The best way to tell is to take the Slingbox out of the picture and test your settop box with both HDMI and Component outputs connected and or disconnect to the TV and then switch the sources while you test them.
The symptoms you've described is indicative of the Slingbox streaming a blank signal to the SlingPlayer. Which probably means the Slingbox itself isn't getting a video or audio signal. You might want to make sure that you've selected the appropriate input from the the Slingplayer. If you're using the Slingplayer for PC check the command bar | Connect | Video Input and make sure that is set the the proper input which is connect into the Slingbox. (And that make sure the settop box is turned on)
My problem is similar with the error message :
"unsupported video signal (1080p) detected.
Ima getting this from my Panasonic Blue Ray recorder connected through component cables.
This device is connected to my tv with an hdmi cable but has been operating successfully for 9 months.
Is it possible the hdmi is causing this problem after being ok for so long?
Any help would be appreciated.
I am away from home at the moment so can't experiment by disconnecting the hdmi.