Theres settings that have to be manipulated on the AV portion. If you are running RCA's at first, hook up your hdmi concurrently and make the adjustment while its turned on. Same for if you are going back. If you have it set for HDMI and turn it off and switch to RCA, fire it up and wait 30 sec. and then turn it off using the power key on the PS3. When you turn it on again it will have automatically reverted back for you.
You need to reset the video setting after using HDMI. I think you hold the power button for a while. Got thsi from the internet.
Make sure the system is off.
Hold down the Power Button for 5-6 seconds - until you hear the second beep.
That's it, your video settings are reset.