This is only for custom firmware , if u don't have custom firmware or simply wanna unbrick any psp see HERE
Recovery mode is one of the most useful features of custom firmware - as it makes your psp almost indispensable. Just assume that your flashed or did something with your psp and you screwed up and your psp doesn’t show anything when you turn it on - its bricked , in the official firmware (and 1.5 running devhook) this would mean you would have to throw your psp or change the mod chip (or use the pandora) . But in custom firmware you have a high chance of accessing your recovery mode though the psp is bricked , this is called a semi brick . In case of a semi brick you can return back to a 1.5 firmware easily and again update to your favorite custom firmware . This is also the same method of downgrading your custom firmware to a 1.5 (that includes 3.40 OE-A) . I would always recommend having the 1.5 recovery in your custom firmwareat all times , in case something goes wrong. So heres the guide (Needless to say for Custom firmware users only),
See the video of 1.5 recovery action at the end of the page :
Semi brick recovery to 1.5 / How to Downgrade a custom firmware OE to 1.5 :
2) Go to your recovery menu ( if you don't know how see the video here ) and choose "toggle USB " - connect your psp to your PC . Make a back up of images , save data , iso's etc that you need .
3) Next Put the PSP folder from the downloaded pack in the ROOT of your psp . If it asks you if it can overwrite click on YES . (Now don't email me asking what is the ROOT of the psp - just google for it in google images )
4)Make sure that your psp is at least 75% charged (100% recommended) , If your psp is semi bricked you cant find the amount of battery left - any how charge it for at least 20-30 minutes better safe than sorry .
5) Also make sure there is a UMD in your psp (any UMD will do) ,This downgrading is SAFE no worries so lets get it done- click on " Run Program at PSP/GAME/RECOVERY/EBOOT.PBP" which is in the main page of the RECOVERY menu.
6) It will ask you if u agree with the risks - just press X . Let it do its stuff after about 2-3 minutes it will ask you to restart your psp manually.
Wait for like 30 secs before manually restarting the psp.
7) yup your done You have a 1.5 psp , You will get that crazy blue screen when you turn on your psp - just press circle and choose your personal settings after which you FORMAT your psp and that’s it !
8) To upgrade to 3.40 OE-A see this guide here