Your psp is 3.90 or 3.90m33-(any number)?You can find this in system
information,if you are 3.90,you need to go to some game shops and tell the
sales that you need to downgrade,it costs $50-$200.but you can also
downgrade by yourself.You can make a pandora's battery,but it may be dangerous because if you miss some steps,your psp will be broken.