ps3 not working with A/V cables after HDMI session

[zoon_ii]

so i bought a ps3 back in march. never had an HD tv, so i used a SD tv with the A/V cables supplied with the initial ps3 purchase.

the other day, i took my system over to a friends house because he has a plasma tv, and i wanted to see what my games would look like in true HD. (needless to say yesterday i irrationally splurged and bought a samsung plasma 42" hd-t4254, monster surge protector, and a tv stand, I'm just dying to put it together and play)

BUT to the original question...

i used an HDMI cable at his house, and when i came back home with the system and tried to hook it back up to my SD tv with the A/V cables, there was only a blue screen, as if it were not receiving a signal from the A/V cables at all.

Now, does this mean that when I was using the ps3 at my friends house that the system set itself up (or maybe me off chance because i was fiddling with settings while we were testing regular dvd movies at his place) to only output in HDMI format? or should it matter at all? I didn't jar the system, as I'm very careful with how I transport it, so physical abuse is out of the question.

HELP!

(PS: i know i now have an HD tv, but still, just in case, if I take over to someone's house that does NOT have an HD tv, I would still like to be able to play the system on their SD tv.)

thanks in advance for any and all insight, clues and help.