I've had problems unlocking an XP1600+. Fill the pits (I used epoxy) and then trim it with a hobby knife so that it is flat with the surface. The problem I had was that there was a coating on the metal pins which are recessed. Only after taking a sewing needle and carefully scraping the tops of these and removing the coating, which was clearly visible under the magnifying glass, was the unlock successful. I had 3 previous attempts. I have unlocked many Duron spitfires and Athlon T'birds successfully and couldn't understand why the proc wouldn't unlock.