Your PSP must be charged to at least 78% . Connecting to a power source during the update is highly recommended to prevent a "power-off brick".
This guide outlines the safest path to bridge the multi-year gap between these firmware generations. psp 352 m33 upgrade to 660
Upgrading a PlayStation Portable (PSP) Go to product viewer dialog for this item. Your PSP must be charged to at least 78%
Use a reliable, formatted Pro Duo stick or a high-quality microSD adapter . Upgrading a PlayStation Portable (PSP) Go to product
To move from an old M33 build to modern CFW, you must first return the system to a clean official state.
Enter the Recovery Menu (hold the Right Trigger while booting) and disable all active plugins to prevent interference with the update process. Phase 2: Updating to 6.60 Official Firmware (OFW)
Updating from such an old custom firmware directly to 6.60 can occasionally trigger compatibility errors. Before starting, ensure the following: