Uncanny X-Men #16

« The Supreme Sacrifice! »: His astral form barely reunited with his body, Professor X deduces that a giant crystal atop a nearby building has been disrupting the Sentinels’ transmissions, even as Master Mold threatens to destroy a city unless Trask keeps building robots. As the Sentinels move to kill their captive X-Men, Professor X and the police arrive with the interfering crystal, deactivating the machines. Trask, cornered by Master Mold’s threats, ultimately turns on the machine and destroys it in a fatal explosion. The X-Men escape the crumbling base, unaware that a new menace awaits them back at the school.