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