
my 6 set PSP ^o^
1st PSP w/ FW 1.00
2nd PSP w/ FW 1.00 update to 1.50
3rd PSP w/ FW 2.50 Multi Firmware Mod 50% success (can't use FW 2.00, 1.50)
    external FW 2.50, 2.60, 2.70
4th PSP w/ FW 1.51 Multi Firmware Mod 100% success
    external FW 1.50, 2.00, 2.50, 2.60, 2.70
5th PSP w/ FW 2.50 Multi Firmware Mod 50% success (can't use FW 2.00, 1.50)
    external FW 2.50, 2.60, 2.70
6th PSP w/ FW 2.01 Multi Firmware Mod 100% success
    external FW 1.50, 2.00, 2.50, 2.60, 2.70
about 50% success :
in new ver PSP (FW 2.50/2.60 from factory)
it use new "protection"
maybe w/ new bootloader ?
so it can not use old ver FW
if you paste old ver FW in it
it will not boot
new ver PSP (FW 2.50/2.60 from factory)
it just can Upgrade
and can not Downgrade !!
How-To : PSP Multi Firmware Mod
copy PSP internal NAND Flash
program it to a samsung 32MB NAND Flash

wrapping Nand bus for external Firmware
