TeamXtreme

Right on the heels of their 2.50/2.60 downgrader, Dark_Alex, Mathieulh, and Yoshihiro have just released a working 1.50 to 1.00 downgrader!

The downgrader uses a method similar to that of the 2.50/2.60 downgrader. At first it was considered impossible, as there was no IPL writing code for 1.00 (since it comes in the update EBOOT file). However, they discovered they could patch the file so that it would write the 1.00 IPL instead of the 1.50 IPL, thus making it possible to load 1.00!

We here at PSP3D.com have tested this, again, and can confirm that it is working.

Mr_Dank (one of the other downgrader testers) of Noobz.eu IRC channel has just released a video of the process and the successful downgrading of a firmware 1.50 PSP to 1.00:

A few details about the coming downgrader:

The downgrader must be run on a 1.50 PSP. It cannot work on any other version.
It currently does not automatically restart your PSP after the process finishes. This should be fixed when the program is released.
You may have to reset your PSP to system defaults after running the downgrader; it doesn't do this automatically.

Naturally, this downgrader will not work on TA-082 hardware PSPs, seeing how there's currently no way to get those down to 1.50 anyways.

Thus far, there have been zero bricks through this method. This isn't surprising; much more is known about kernel-mod execution in 1.50 than in 2.50 or 2.60.
Password for the archive is: I_Use_It_At_My_Own_Risk

Update 1: You cannot run Devhook or ISO loaders under 1.00, apparently. This isn't because it's impossible; it's because they're specifically coded for 1.50. Also, you'll want to avoid programs such as Flashmod or X-Flash, since the files in flash0 under 1.00 are not the same as those under 1.50, and overwriting them with improper files could brick your PSP.

Update 2: The latest version of the MPH Firmware Loader also does no work. Again, this is because it's specifically coded for 1.50.

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