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I got bored with the games that are out for the PSP right now, so I decided to have fun with it another way.
I know Red Boxing is a bit out of date and doesn't work everywhere anymore, but it's still a neat trick.

Check out how to make your PSP into a Red Box at:
[censored]

~Ph0tek

well, if you update to 1.51 and want to downgrade, i guess it'd be possible if when you went to flash it, the psp saw the Jap. 1.51 as something irregular and would go ahead with installing the US 1.5 back onto it.