So, I was able to get the PSP Testing Tool (DTP-H1500) to boot into service mode (not in the "official" Sony way). :p Long post warning?
The typical service mode/Pandora's battery works by putting in a PSP battery which contains the EEPROM serial 0xFFFFFFFF which the SYSCON reads...
Obscure Gamers is a Video Game Preservation group founded in 2017. We actively work to preserve long lost video game history & hardware for educational research and historical purposes. Our long term goal is to work with Video Game Developers in preserving this important history from being lost.