From Pspupdates.com


Welcome to 1.50, PSP firmware 2.0 users! MPH has created a WORKING downgrader from PSP firmware 2.0 to firmware 1.50. This takes advantage of the toc2rta exploit and allows for the full downgrade of firmware 2.0 to firmware 1.50. I have tried this myself and have successfully downgraded from firmware 2.0 to firmware 1.50. Homebrew and UMD games WILL both work after the downgrade.