Si j'ai bien compris, il fonctionne que pour les ex-1.0 !
Source:http://pspupdates.qj.net/-Downgrader-for-1-0-PSP-Users-Go-back-to-1-0-after-using-1-50-Firmware-/pg/49/aid/44226
"That mad scientist 0okm is at it again. And this time, it's something pretty revolutionary. He has just managed to write a program which can flash your 1.5 PSPs to 1.0, provided that you've backed it up using his tool. This isn't a true downgrader since you can't actually downgrade your original 1.5 PSPs, or even the 1.0s unless you've backed up your firmware with it. But if you're one of those lucky people to still have a 1.0 PSP, rejoice! You can actually take a trip to the 1.5 firmware, and come back home to 1.0!
How is it possible? Well, in simple words, it's just copying the firmware to the memory stick and later, just re-flashing it again. But then, why wouldn't a normal firmware file work, like in the 2.0 downgrader? Under the circumstances, I'll assume that all the files in the flash are somehow encrypted differently for every PSP. That's why it isn't accepting files from a different PSP. It will only restore your firmware if the backup is taken on your own PSP.
And this comes from the guy with the multiple firmware hack which we covered some time back. Seeing all his wacky projects, I'm pretty much sure he has a bunch of stuff up his sleeve. What exactly, I can't tell you because I myself don't know. But whatever it is, I'm waiting with bated breath. For now, enjoy this backup and restore tool for your 1.0 PSP.
The download file is locked by a password. You should open the attached README and find it out yourself since it carries an important message. Please make sure to read the README because it also mentions a lot of info which you should be aware of before embarking on this adventure. And as with every firmware tool, it is risky. Make sure you know what you're doing. Neither 0okm, or QJ.NET accepts any responsibility if you burn your hands badly with it.
But if you're still dying to try it, download it using the link below. And thanks for the tip i386!"
Pour le télécharger : http://dl.qj.net/index.php?pg=12&fid=7902