One of the consistent problems that the PSP has is the lack of support for homebrew programs. Back when it was released, this wasn’t much of a problem, because people could easily create downgraders and install applications as they wished.

But ever since version 2.0, the only way to make your PSP able to run homebrew is by using the Grand Theft Auto game that has a security vulnerability that allows you to access the console’s kernel. This latest downgrader is no different, you will still need a copy of GTA: Liberty City Stories. Here are the steps that you need to follow:

1. Update to firmware 3.03. If already have this firmware then proceed to step 2.
2. Open the 3.03 downgrade file and copy the contents of the folder MS_ROOT to the root of your memory stick.
3. Open the 1.5 update and rename the EBOOT.PBP to UPDATE.PBP then copy it to /PSP/GAME/UPDATE/
Make sure not to overwrite PSP/GAME/UPDATE/EBOOT.PBP
4. Load Grand Theft Auto: Liberty City Stories (unpatched)
5. It should get to loading save game, clear the screen, the screen should fill with a light blue color and then reset the PSP
6. Check that HEN is running by going to system settings then System Information and it should show up as system version 303 HEN
7. If it is showing up as 3.03 HEN then go to the memory stick and run the x.yz update
8. Before the downgrader does anything to your PSP it will ask for you to agree to what it is doing
If you no longer want to continue press the Right Shoulder Button (R-TRIGGER).
9. Once you have agreed to start the downgrade do not unplug the PSP
10. Once finished the PSP will ask you to press X, after pressing it will reset it self.
11. If it comes up saying that the settings are corrupt press X to continue.
12. Enjoy your new shiny 1.5 PSP.

If you notice those steps carefully, you’ll realize that there are two version of the Liberty City Stories game. One is unpatched, and allows you to load homebrew applications, or even downgrade the console, the more recent version is patched, and therefore you can’t use the same exploit.

How can you tell if your copy of GTA is patched or not?

Unpatched versions of Liberty City Stories contain the 2.0 update, whereas patched versions contain higher updates. If your copy of LCS has an update higher than 2.0 on it, then you will have to find an unpatched UMD to proceed.

If you manage to get an unpatched version of GTA, and manage to get your PSP to an older firmware, then you can install a custom firmware and start enjoying homebrew software on your console, like console emulators, classic games (like Quake), or to have the ability to convert and run your Playstation 1 titles from it.

You can find more information in the original article.

Steps to use the MPH downgrader:
- Create an UPDATE folder in PSP/GAME/ folder of your memory stick
- Copy EBOOT.PBP (update 1.50) in /PSP/GAME/UPDATE folder
- Unpack MPHDowngrader.zip
- Copy overflow.tif in your PSP/PHOTO/ folder of your memory stick
(make sure you have changed your background to frame_buffer.png as explained in the toc2rta exploit.)
- Copy h.bin in root of your memory stick
- Copy index.dat in root of your memory stick
- Plug the AC adaptor

What you do next is go into the Photo Menu on the PSP and it will show some jumbled text, which is normal. Wait about 30 seconds and then restart your PSP.

From there you will now have a new file in your PSP?s root directory called ms0:/index.dat.bak. In the next step you will go to you Game Menu, Then Memory Stick, and then Launch ?PSP Update ver 1.50.?

It will then ask you to downgrade and lead you along to installing. Here is where I got scared. It installed to 99% then errored. This is OK. Restart your PSP and reboot it. It will come up with another error which is OK as well. Restart it again and you will have PSP firmware version 1.50. Enjoy, and welcome to the world of legal homebrew, not piracy.

Grab the downgrader.

Grab the 1.50 update eboot.

Remember: use this at your own risk, and if you enjoy any software you try: support it!