If you have accidentally upgraded to 6.60 OFW and found yourself with your ISOs no longer working, you’re in luck. PSP Developer some1 (of 6.xx to 6.20 downgrader fame) has released a new version of his signed downgrader which will allow you to downgrade your PSP to 6.39 OFW, 6.35 OFW or 6.20 OFW.

Update: If you don’t want to downgrade, you can install 6.60 PRO-B9.

Simply visit my updated Downgrade your PSP to any 6.xx OFW guide for more information.

Important note, this guide is formerly just a post for 6.38 to 6.20 downgrade. Since some1’s latest update now supports 6.60 OFW, I opted to change the guide to completely encompass every 6.xx OFW. I’ll be updating the Dummy’s Guide accordingly as well.

Credits go to:
some1 for the v4 of his PSP Downgrader
Davee for the initial downgrader release