Star Trek: The Animated Series, season 1, episode 8
The Magicks of Megas-tu
Summary
While exploring near the center of the galaxy, the USS Enterprise is caught inside an energy/matter vortex and all her computer systems fail. A being named Lucien appears on the bridge, repairs the ship's systems and takes the crew to explore his planet, Megas-Tu.
Summary from Wikipedia, CC BY-SA 4.0.
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