Although this has been tried and found working, this does not mean there is no risk involved so use at your own risk.

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.

1005K 2.00에서 TEST결과 성공했습니다.^^