Just found this webpage on how Sony unbricks PSP's
I don't know if this has already been posted but it seems like the kind of thing that I am sure everyone would like to read anyway. It shows the EXACT procedure Sony uses to unbrick PSP's. It may or may not be fake but in either case, it makes for an interesting read.
Linky - http://boardsus.playstation.com/rss/...age.id=2665495
The remote control (PSP-120) of the Sony PSP is actually replaceable with a more feature rich version found on many Mini-Disc and Walkman Disc players. For example, you can substitute one of those remotes that actually display the songs being played on small LCD displays. However, on some of the remotes you may need to lop off the plug and rewire the lines to use the PSP-120 plug (which is 6-pin: 3 on top and 3 on bottom). Note that the remote control port on the PSP provides dual purposes. Besides providing headset and remote control functionality, it can be used to initiate special commands to the PSP. Provided you have the correct gear, and have sent the correct communication (via RS232 at 4800 baud) via the remote control port, you can even send new code for execution and put the PSP in a special diagnostic mode. It is known that via this port the PSP is reset to factory default state before it is shipped, and to restore bad firmware flashes. It is unlikely that whole firmware codes are transferred on the remote control port at 4800 baud because sending multi-megabyte code at 4800 baud would take too long. Flashing new firmware via the USB port (because of bad firmware install) is impossible because the USB port is off by default when you first turn on the PSP (this is why you need to select Settings --> USB Connection before you can use any USB devices).
So is it possible to create whole new operating systems by simply reflashing the PSP's firmware?
Yes, but the firmware must be in the correct format and encrypted with the correct key (which only Sony knows). But since the firmware provides basic hardware operational functionality, the OS can reside on the UMD or memory stick, so re-flashing the firmware may be going a little overboard. The PSP can also function as a dummy UMD device (like a CD-ROM drive in a PC). You send commands via the remote control and the PSP would return data from different sectors of the UMD disc via the headset port.