My PSP has all symptoms of a defect analog stick: in GTA the character runs around in circles without me touching any buttons and in Assassins he will walk forward all the time... So I replaced the analog stick, switched on - and the problem persists. I then removed the analog stick completely, but the problem is still there.

So I guess it's not the analog stick that is causing the problem - BUT what is it then?

Any ideas and suggestions?