PS3 Debug Firmware v4.20 (DGF) Downgrade File Update for use on TEST consoles only.
More details: http://www.ps3news.com/ps3-hacks-jai...e-more-arrive/
4.20 DEX Downgrader
Description: This file enables you to downgrade again from 4.20 DEX to a lower firmware version.
1. Create a PS3 folder on a FAT32 formatted USB stick
2. In that folder create a "UPDATE" folder
3. Copy this PUP inside that "UPDATE" folder
4. Insert the USB stick in your PS3
5. Go to system and update your PS3 through "Update via Storage Media"