Downgrade from preinstaled 3.50 fw

[vale87]

I have two PS3 one is 320GB CECH-2503B, one is 160GB CECH-2503A. I have tried everything ( 3.41 modifed, 3.15 debug.........) nothing worked!!!!!!!!!!!! Flashing green NON stop.

any idea? I think any PS3 come with CECH-2503............ and 3.50 can not be downgraded. coz Sony did something into chip which preventing downgrade.

My slim is 160gb cech 2504a. It came with 3.40. The thing i dont understand is, is it about the fw it came with? or can it be because those are newer models? its strange.