I was thinking could it be possiable to hack the eboot file for version 1.5 to look like it was say 2.1 ? Then when you try to boot it since it would be an offical piece of code and not some homebrew thing. The psp would run it and install the earlier version of the firmware thinking it was an upgrade. I don't know how to hack the file or I would try it. But I did see on this site that someone was able to trick the psp into starting to run a bit of homebrew code on a 2.0 machine by tricking it into thinking it was a firmware upgrade. Although the code did not run I was thinking it would work if it was an offical firmware eboot file.

Now, now boys... allow me.
Flame, flame, flame
search!
If ur mother had a tooth for each time this was asked, she'd be a t-rex.
Warning: Downgrader thought-up shortly following blunt head trauma.
I'm surprised noone else thought of this.

Hey mods.... slam the door!

Yeah try this!!

BRICK!!!!!!!!!!!!!!!

actually.. this has been done befor by somebody..

and it didnt brick the psp just so u all know..

he got an error.. matter of fact im sure hes still playin around with it

your spelling of the thread title proves you are a noob