New MPHDowngrader v1.0.1 is much easier
Only for psp v2.0
if you have a v1.51+ you must upgrade to v2.0 before downgrading to v1.5

http://mphwebsite.tuxfamily.org/index.php?program=9
click on link go to Files and download MPHDowngader v1.0.1

Installation :

– Create a UPDATE folder in PSP/GAME/ folder of your memory stick
– Copy EBOOT.PBP (update 1.50) in UPDATE folder
– Unpack MPHDowngrader.zip
– Copy overflow.tif in your PSP/PHOTO/ folder of your memory stick
– Copy h.bin in root of your memory stick
– Copy index.dat in root of your memory stick
– Plug the AC adapter

with this downgrader it take like 2 sec with no errors to downgrade to v1.0

then when you load upgrade 1.5 it will stop at 99% and have a error Just power Off Psp then turn on
you’ll see a screen with alot of text just press O and Done you now have a 1.5 Psp