D84 uses the final deactivator. (TV: The Robots of Death)
The "final deactivator" was a device created by the Fourth Doctor to disable robots aboard Storm Mine 4 at close range. He built it, in part, from the head piece of a broken Voc.
After being restrained, the Doctor dropped the activator. Despite being heavily damaged by a laserson probe, D84 dragged itself over to the device and used it, destroying both itself and the nearby V6. (TV: The Robots of Death)
