After going to Mean Street North for the second required visit go over to either of the ways you used to get to the D.E.C. on your first visit. After that go to the upper level behind the wall and parallel to the Main Area. Talk to Jamface who is next to the building. Give him some scrap metal and he will repair it.
Near the machine is a contraption that has two white toon panels. Thin those out and have Oswald shock a nearby panel. The machine will explode and send metal all over. It also gives you a silver pin.