So since the PSP is hacked to **** — and Sony isn’t suing anyone who targets it — developer some1 has released PSP Downgrader v4. And in addition to 6.60 support you can now downgrade to any official firmware, but — more on that after this…
This downgrader, originally developed by Davee for 6.31 and 6.35, which some1 ported to later firmwares — 6.38, 6.39, and 6.60 — now lets you downgrade your PSP not only to 6.20, but any official firmware (OFW) you so desire. Although with that, comes this: You can only downgrade to a firmware greater than or equal to the factory installed OFW when your PSP was purchased; this downgrade has not been fully tested with all the different PSP models and OFWs; I wouldn’t try anything silly, like jumping way back to firmware 1.50; we are not responsible if you damage or brick your PSP.
The firmware 6.60 downgrade is made possible by a (new?) kernel exploit discovered by Davee; that was then passed down to Zecoxao, who later made said exploit available to some1. So mad props to everyone — full circle!
Downgrade your PSP from firmware 6.31, 6.35, 6.38, 6.39 or 6.60 to any desired [official] firmware ... as long as your desired firmware is greater than or equal to the factory installed firmware (OFW) when you purchased your PSP.
This is a port of Davee's 6.31/6.35 downgrader, released by some1. Click here for more info.
Added Support for 6.60
Fixed 6.60 problem that didn't allow to downgrade to anything greater than 6.20, thanks to Davee
Allows any updater that is greater than or equal to the factory installed OFW (Has not been fully tested, will most likely work on 5.00 and up)
Special Sauce added by Proxima
If the 6.20 updater MD5 check fails, it will check if the update file is 6.35, allowing non 07g/09g to downgrade to 6.35
includes source code
removed a few debug printf's
fixed bug for 6.38 created when adding 6.39
added support for 6.39
added model printer
09g/07g support added.