As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER DEPARTURE, SMOKE WAS OBSERVED IN THE CABIN, ALONG WITH A CAUTIONARY EICAS MESSAGE LT COOL TURB HOT. CREW SELECTED THE L PACK TO OFF, SMOKE SLOWLY DISSIPATED AND FLIGHT DIVERTED BACK TO DEPARTURE. REMOVED FAILED LT COOLING TURBINE AND INSTALLED OVERHAULED UNIT , ALL WORK PERFORMED IN ACCORDANCE WITH MSG3 AMM 21-01-09 AND AMM 21-00-00