To all/the few of you who have a PSP that is 2.5/2.6 firmware that was originally under 2.5 and you upgraded and want to downgrade, news has been rapidly spreading of a downgrader that... well... downgrades to fw 1.5.
Several limitations come with this:
A) You must have upgraded from 1.5/2.0/etc. to 2.5/2.6. Not for factory 2.5's.
B) Your PSP mustn't be a TA-082. To check this, look inside the top-right corner of the UMD drive. If there is a IC1003, that's a bad thing. If there's nothing, you're in the clear.
(Another interesting tidbit, if your PSP is TA-082, you won't be able to use the modchip, either. Fun fun.)
C) You need a PSP with 1.5 firmware, whether it be your friend's, brother's, mom's, or whoever's.
D) A USB cord connection to PSP.
E) A CLEAN eboot of the 1.5 firmware, found here:
http://dl.qj.net/psp-firmware-1.50-f.../163/catid/163
I say clean because many 1.5 eboots are tampered with and can brick your PSP.
F) A copy of Grand Theft Auto: LCS
G) The eLoader:
http://www.fanjita.org/
Click on eboot loader and scroll down to the automated installer file and follow the insructions from there.
I would also like to state that in order to run Homebrew games and apps, you don't really need to downgrade. All you need is Grand Theft Auto and the eLoader. However, some people prefer the downgrader, like me. But hey, it's your PSP.
You also need the Helper, (which goes on the friend's 1.5):
http://dl.qj.net/1.50-helper-%282.5-...8541/catid/151
And the downgrader itself:
http://dl.qj.net/index.php?pg=12&fid=8566
Remember to unzip the junk.
KEEP IN MIND: THIS HAS NOT BEEN FULLY PERFECTED AND NOT GUARANTEED TO WORK. So if you brick your PSP, it's not my fault.
With that in mind, we proceed.
1) Hook up the 1.5 PSP to the computer via USB and set the Helper into the PSP games folder. I can't remember whether or not you put it in a folder called "Helper" or not. If it doesn't work the first time, either put it into or take it out of the folder (which you have to create.)
2) Take the 1.5 firmware eboot and put it into a folder in the GAMES section called "UPDATE" in all caps, (which you also have to create).
3) Lauch the 1.5 Helper app, which should be in the games section on the PSP. It'll run for a long time. What it's doing, basically, is copying all of the essential 1.5 files and tossing them into a file called Downdater on the root of the memory stick.
Congratulations, you no longer need your friend's 1.5 PSP.
4) Pull the Downdater folder from the 1.5's root and put it onto the root of whatever PSP you're downgrading.
5) Now, put the Downgrader itself into the GAMES folder.
6) If you don't know how: Refer to the various guides around the internet on how to get GTA and eLoader to run eboots. This guide is already looking a bit long and I don't want to go into explaining that here. I find
http://www.psphacks.net/ to be very helpful.
THIS IS THE POINT OF NO RETURN
7) Start the Downgrader through GTA.
8) It may look like it shut itself off, but, as you can see, the memory stick light is flashing, meaning it's working.
9) Leave it for a minute or so after it looks done, just to make sure.
10) Afterward, it'll look like it did when you first bought it.
If you get a UMD load error, shut down the PSP completely and remove the battery for about five minutes.
Congratulations, you now have a 1.5fw PSP, and if you haven't checked already, GTA should no longer work without upgrading to 2.0. YAY.
For further info, I HIGHLY recommend checking out
PSP Hacking 101.com and checking the forums and watching some of the many videos.
I based this guide off of episode 17, the newest one.
And that's all there is to it. Downgrading your PSP in 10 easy steps.
If you brick your PSP screwing this up, it's not my fault.
Ow, my hands hurt a bit. So does my sunburn. Anyway... you're welcome. And don't say I don't contribute anything.
!
), you can download the games from the Store already and transfer them to the PSP when 3.0 comes out. 
Linear Mode
