is there a way you can tell which motherboard without opening the psp ??
can I upgrade from 2.6 to 2.71 then downgrade back to 1.5 ?
do I need another psp with 1.5 files ??

yea, from what i know of theres atleast 2 mobo types the TA-082 (the bad one)and the another a 11103 type or something? anyway if you open up the UMD if you see a copper board name on the upper right corner its a TA-082 board. if there is no number in the top right corner its on the bottom left, and is the GOOD one.
(EDIT:) i forgot to add, you dont necessarily need another PSP as long as you can find a 1.5 DOWNDATER folder with the right contents inside. I sure as hell do not have 2 PSP's.

and yeah, you can upgrade to 2.71 and then back down. thats how most of us got there in the first place.but make sure its at 2.71 and not a TA-082 board