Which PSP(s) cannot be hacked with CFW?

[Nechen]

I have a PSP Phat that is currently bricked and am currently bidding on a PSP Slim on eBay thats up to $13.50 with 20 hours left.

I've read that some PSPs can't be hacked and I was wondering if these were random PSP2000's or the PSP3000 or what the story was.

Its pretty impossible to tell even with this info because he only states that its a Slim that he got "awhile ago"

[Nokiaman]

1)These which have G under Volts,but I guess he doesn't have box of it
http://en.netlogstatic.com/p/oo/019/990/19990035.jpg
2)Or this tester (http://rapidshare.com/files/151449590/TA-088v3_Identifier.rar) can test it