Voilà j'ai trouvé ca :
Some thought it might be impossible, others simply felt that only God's hands could code a software downgrader for the unfortunate TA-082 people. Well, let's just say that 0okm might have finally broken the shackles imposed by the TA-082 PSPs.
Firstly, a small primer for anyone new to the whole TA-082 thing. A while back, before the Undiluted Platinum modchip came out, most people were quite oblivious to the whole mobo-mania. Then it was revealed that the modchip wouldn't work with the TA-082 motherboards. Even Dark_Alex's "downdater" couldn't downgrade 'em. Few people who were brave enough to still try it were greeted by shiny bricks. Here's how you can check if you're one of the unlucky ones to have a TA-082 mobo PSP.
The reason was quite unknown. A lot of theories existed, but it was difficult to pinpoint the real problem. Well, we can safely consider it as part of the past now, because 0okm states that he has successfully downgraded a 2.50 TA-082 PSP using a software downgrader. Until now, the only other way to accomplish a downgrade was by using hardware hacks, like 0okm's multi firmware module.
Not anymore though, because we might just have a solution for the TA-082 motherboards! Here's what he states in his blog:
"Success SoftDown FW2.50 TA-082 to FW1.00/1.50
Had found a method SoftDown TA-082's FW2.50 PSP to FW1.00/1.50
But the method is quite complex, SoftDown a TA-082's PSP need about 45min
1. Use software Read Data From TA-082's NandFlash & DDR DRam
2. Analyzes the Data than make a "FW1.00/1.50 NandFlash img" that can Boot on TA-082
3. Use software Write that "FW1.00/1.50 NandFlash img" to TA-082
maybe late i will make a software to let "FW2.50 TA-082" user to dump "NandFlash & DDR DRam" data to me
than i can make the "FW1.00/1.50 NandFlash img" to help them SoftDown their TA-082 
"
Well, so the method might take a while and it might be a bit complex. But trust the great programmers to make an easy installation method for everyone to use. 0okm has said that he might release something as a proof of concept. Keep the fireworks ready!
D'après ce que j'ai compris, Ookm a réussi à downgrader une PSP équipée d'une carte mère TA-082 mais cette fois-ci il a réussi sans matériel externe !!! Juste avec une solution logicielle !! Le downgrade est très complexe et il a duré 45 minutes !!!
0okm a dit qu'il pourrait relâcher quelque chose comme une preuve de concept.
Petite précision qui a de l'importance : le downgrade est pour le moment compatible qu'avec le firmware 2.50 (et pas le 2.60) !!
Source :
http://pspupdates.qj.net/Downgrader-...g/49/aid/62647
Blog de Ookm :
http://0okm.blogspot.com/2006/08/suc...ta-082-to.html