Homebrew developer Dark_AleX has released an update to the 1.50 kernel add-on for Phat (regular) PSP units running custom firmware 3.90 M33. The update adds support for memory sticks greater than 4GB in size under the 1.5 kernel and fixes a display bug that affected TA-86 units when resuming from sleep mode.
To install, first download the 150.PBP and place it in the root of your memory stick (X:\150.PBP, if X is the drive letter of your PSP). Then simply copy the "150k_installer" folder to GAME and run the installer from the PSP's Game menu.
Download 1.5 Kernel Add-on v2 For 3.90 M33
Dark-AleX - PSP Developer [Dark_AleX]