A semi-bricked PSP is a PSP that turns on but only displays a black screen. This is a sign of a software corruption that can only be fixed in one or two ways. The first way is to send it back to Sony which could cost up to £65. The second way is to use a PSP tool known as a service tool. The service tool gives you access to enough of your PSP's file system to reinstall the PSP software and return the PSP to a fully operative state.
Plug the MMS and service tool into the PSP. The service tool appears as a normal PSP battery and is connected via the PSP's battery insert on the back of the PSP.
Turn the PSP on while holding the left "Trigger" button. This activates the PSP's service menu.
Press the "X" button on PSP controller and the PSP's software is reinstalled over top of the corrupted PSP software. This returns the PSP to its full usability.
Connect a charger to the PSP and allow the PSP to charge with its normal battery inside. When the charging light turns off, the PSP is completely charged.
Turn the PSP on and update the PSP's software using the normal update method. Select the "Software Update" from the PSP menu and the PSP is updated to the most recent PSP software release.
Service tool batteries can be found online for purchase. The MMS is what holds the software that is installed from the service menu. MMS stands for magic memory stick. These come packaged with the service tool.