Downgrading a 3.90 PSP Slim?

I have a Japanese PSP Slim with North American 3.90 OFW. It came with 3.80 and I though I'd update it to get Skype, but turns out it doesn't matter what region 3.90 you have, just what region PSP you have. So I want to put custom firmware on it so I can fake the region.

My question is: I can only find 1 tutorial on how to use a Pandora's Battery to downgrade a Slim on this site, but it says I NEED 3.60 OFW on my Slim. Is there any other way to do this with any firmware on the Slim? Or am I stuck with a 3.90 Slim?

You an downgrade any firmware.

Okay, good.

But I thought the PSP Slim couldn't handle 1.50 for some reason.

[brentbizzle]

Technically with the Slim is isn't downgrading... its reflashing the firmware with a custom firmware.

Technically with the Slim is isn't downgrading... its reflashing the firmware with a custom firmware.

And there in lies the problem. All the tutorials I can find and all the programs I can find need the slim to have 3.60 on it. The PB with the modded MMS flashes 3.60 into 3.60 M33. Trouble is, I can't find a mod for the MMS that will flash 3.90 into 3.90 M33.

Am I just not looking in the right places?

Sorry for budding in, but could you downgrade a slim using a Pandora battery? And then using the Time Machine hack?

Are you talking about the 1.50 pandora or the one that redirects your firmware to a CFW version?
The Time Machine Hack simply allows you to boot 1.50 off your memory stick, and from there you can play 1.50 homebrew. It is basically running your computer in compatibility mode on 95' when you are on XP, in order to play some game. It isn't a downgrade .