The Source
The Source was a bioelectronic source of power that the Keeper of Traken, who ever was elected at the time, used to keep the peace in the Traken Union civilisation. The Source was something of rarity as the Traken Union were using it to stop evil attacking the civilisation.
Melkur
During The Keeper of Traken Tv Story , The Melkur takes control of the Source from the Consul Kassia who dissappears when the Melkur materialises in her place.
Sabotage
In order to stop the Melkur, Adric and Nyssa create a servo-shutdown which destablises the Source stopping Melkur controlling it. The Doctor, after escaping The Master ,then cracks the source encryption and reversed.