Amazing Spider-Man #329.
Sebastian Shaw had started on a project concerning Sentinels and after Loki’s defeat by the Avengers in the latest issue of West Coast Avengers, Loki decided to cause some problems on Earth, making the sentinels to merge to become the Tri-Sentinel. The Tri-Sentinel went flying in New York, while Sebastian Shaw had gone to investigate Spider-Man’s new powers’ source. He found the professor that had inadvertadly brought the Enigma Force to Spider-Man. Now, Shaw wanted the professor to use the machine to take away Spider-Man’s new powers, but as the professor used the machine, the Enigma Force got a better hold of Spider-Man and the transformation was complete. Spider-Man managed to destroy the Tri-Sentinel. When his mission was over, the Enigma Force took away the new powers.