Their is in fact a downgrader for 2.71 that uses a tiff exploit ( all psps are compatible), their are two versions... a Ta-082 version and a normal one.
The Ta-082 version will be harder to do so because that means that vital firmware files are within the motherboard, so the files must be patched. ( a seperate downgrader from the normal one will do this automatically for you)
TO INSTALL:
You'll need this first (Hen)
It allows you to run unsigned code for the moment ( long enough to downgrade)
Then use one of the 2.71 downgraders depending on which version you have
normal
(Ta-082)
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