DVD picture too small using component cable

my dad has a cheap Sony DVD player and a Vizio 42" plazma TV and I hooked it up using component cables. I was surprised to see the picture did not fill the screen. It is stuck in the 4/3 spot (though widescreen mode) to explain: there are black bars to the sides and above and below the picture.

I have a Muse DVD player and 50" Vizio and I use component cables and it fills the picture completely or it may have black bars above and below but never on the sides.

Is this because the Sony DVD player is too cheap or too old? (it is both) What can I do? I went thru both carefully and could not find a resolution adjustment - I presumed the component cables determined that anyway...

thanks for any info!

Phil