See if any of the following articles can help:
* [https://discussions.apple.com/thread/8162298|Airport is warning of overheating] - ASC
* [https://discussions.apple.com/message/32262252#32262252|why is my airport extreme overheating] - ASC
* [https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwjO_9_CiI_YAhXMz4MKHTlYAxsQFggqMAA&url=https%3A%2F%2Fwww.ifixit.com%2FTeardown%2FAirPort%2BTime%2BCapsule%2BA1470%2B%2528Mini%2521%2529%2BTeardown%2F15067&usg=AOvVaw2azjFhDVNzM__chnZl7_I3|AirPort Time Capsule A1470 (Mini!) Teardown] - iFixit
* [https://sites.google.com/site/lapastenague/a-deconstruction-of-routers-and-modems/apple-time-capsule-repair/repair-ac-version-time-capsule-or-extreme|Repair AC version Time Capsule or Extreme] - LaPastenague