とても いい しつもん です。 (Very good question!)
One thing to note is the ending ~へん, surely you've heard people say, わからへん！ *(wakarehen)* which is the equivalent of the standard tokyo-dialect わからない！ *(wakaranai)* _"I don't understand!"_.
If you ever hear _"something-something ~へん"_ you can assume that it's _"something-something-NOT"_ as in, ~へん = ~ない.
*たべる → たべない → たべへん → たべへんかった*
_I eat → I don't eat → I don't eat → I didn't eat_
_(dictionary form → standard negative form → kansai dialect → kansai dialect -past-form)_
Another funny point is that instead of saying だめ [as in, _"no", "it can't be done"_ - a negative answer] Kansai people say あかん *(akan)*.
And finally, as you've noted, in Kansai-dialect, the だ *(da)* is replaced by や *(ya)*, such as:
*なんだ → なんや*