Throughout the releases of custom firmwares, there has been many recovery methods developed to restore full functionality of the system from a semi-brick or a full brick. (Depending on method used). But there is one situation where this cannot be done so far!
If you are one 3.71 M33-2 , or going to downgrade to that, please upgrade to 3.71 M33-4. A nasty bug has been found in 3.71 M33 and 3.71 M33-2 that will corrupt your flash0, and lead to a brick. If you do not have a Pandora Battery, you will not be able to unbrick your PSP. This also applies to users of the UP modchip. For more info on the UP bricks, click here
In the Summer of 2007, Team C + D and a bunch of other homebrew developers created an universal unbricker for Phats, and downgarder in one. (Slims weren't available at the time) With the use of a battery converted to Service Mode - called a JigKick Battery and a Magic Memory Stick that held the firmware, and the special ipl for booting to the Service Menu, any Phat could be downgraded and unbricked to any firmware that was already existent, and dumped . The most popular of these firmwares were firmware 1.50. However, the next month, the PSP Slim was released, and lacked support for the 1.50 firmware, and could not boot properly to Service Mode. 5 day passed after the release of the Slims, and it was found that a modified version of Pandora's Battery that installed custom firmware instead of downgrading the firmware; was able to work on a Slim. However, this method only installed 3.60 M33, and flashed back to 3.60 leaving the official firmware files in tact. This method could not fix any kind of bricks on the Slim. As firmware 3.70 rolled out for the Slim, this method of installing custom firmware was no longer of use. Pandora's Battery still proved useful. Over time, there have been various expansion apps for a magic stick that expanded the possibilities of unbricking with Pandora.
When firmwares 3.71 and 3.71 M33 was released, Dark_Alex developed a way of installing custom firmware through the use of Pandora's Battery. This was a full universal unbricker and worked perfectly on a Phat. The install process was somehow similar to the original Pandora unbricker method, and it required the properly formatted memory stick, and the right ipl written. (As well as a memory stick between 128MB and 4 gigs, and to be real.) 4 versions of Despertar Cementerio has been released with version 3 adding kernel support for a Slim allowing the service menu to be displayed. Versions 1-3 installed 3.71 M33 and the Sony counterpart, and version 4 installs 3.80 M33 and its counterpart. Within Despertar Cementerio, there are options to back up and restore nand images. However, this way of unbricking can prove disastrous to the uneducated user. (A NAND image contains firmware, and IDStorage Keys which are vital for proper operation of a PSP. The keys and nand are unique and specific to each PSP)
Other methods of recovery
Developers have been able to develop their own means of recovery for specific reasons that makes use of a Pandora Battery. One example of another recovery method is from FreePlay of QJ.net, that allows Slims to have 3.60 reflashed and working.
Recovery to 3.60
FreePlay of QJ.net has developed a way of reflashing firmware 3.60 onto a Slim with a Pandora setup that is capable of running ELF files. However, this method requires a full dump of the 3.60 firmware from a Slim, and 3.60 ipl. However, this method has no safety checks so if anything done during preparation was incorrect, the user might have bricked their system. Also, this is a Slim-only recovery so if attempted on Phats, it will brick those systems as well. (Since the Phat 3.70 was the Slim equivalent to 3.60)
Hellcat's Extended Boot Menu
Aside from Despertar Cementerio, Hellcat has developed a Pandora Extended Boot Menu (EBM) where adds more options to the original Pandora setup. This includes USB, booting to a dumped firmware, launch a CFW installer directly, or launch an app that has access to flash0. (Or can just be simply used to launch any app). However, this menu is for Phats only.
UPMS (Ultimate Pandora Magic Stick)
This is a freeware project app, which can format Memory Stick and install on in Despertar del Cementerio v3 & v4 , Hellcat's EBM, Jas0nuk's ELF menu and some utilities so that they could be launched from service menu.
On every custom firmware since 2.71 SE, there has been a way to recover back to 1.50 to fix semi-bricks that occurred while on the firmwares. This only worked on semi-bricks where the recovery menu was still accessible. There are various recovery downloads available for SE, OE, and M33 firmwares. However, this method will not work on a Slim due to no kernel support for 1.50. Most recoveries will downgrade without fail. However, attempting a recovery from the newer M33 firmwares to a lower SE/OE firmware will result in a full brick. There is recovery available for every version except for 3.80, and 3.90 M33. However, the 3.71 M33 recovery may sometimes work with the newer firmware.
Pleas take note of the description of each download.
3.71 M33 - Recovery for 3.71 M33 Phats!
Recovery for SE/OE and 3.52 M33 - Phats only!
FreePlay's 3.60 Recovery - Slims only!
Despertar Cementerio v4 - Phats/Slims
Hellcat's EBM - Phats only!
Pandora battery - Phats only!