Over hot, not boiling water, combine chocolate chips, 1/2 cup sugar and coffee. Heat until smooth. Remove; set aside.
Combine wafer crumbs and butter. press firmly onto bottom and up sides of 10-inch springform pan.
In bowl, beat cream cheese until fluffy. Gradually beat in 3/4 cup sugar. Mix in sour cream and vanilla.
Add eggs, one at a time. Beat well before adding the next one.
Divide batter in half. Stir melted chocolate into 1/2 of the batter. Pour into pan. Cover with plain batter. With a knife, stir chocolate batter through making a marble effect.