Valderon (planet)

You may be looking for Valderon the Mind-Slaver.

Valderon was a penal colony planet during the 36th century. Nyssa's son Adric spent time there conducting research to find a cure for Richter's Syndrome. The Fifth Doctor met his original TARDIS there after he landed on the planet in 3556. The Type 50 had spent twenty years on the planet, damaged heavily after leaving Gallifrey in pursuit of the Doctor, and it had become Sibor's "chronoscope" when she discovered the timeship could see into the future, and used it as a means of controlling the population. The Type 50 TARDIS used its telepathic circuits to give the natives "the gift of tongues," while trying to find someone it could control while it planned to rebuild itself. (AUDIO: Prisoners of Fate)