As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COCKPIT HAS BURNED SMELL AND VISIBLE SMOKE WITH APU ON AND ISOLATION VALVE OPEN. SMELL AND SMOKE SEEMED TO DISIPATE WHEN PACS SHUTOFF AND REAPPEARED WHEN TURNED AGAIN. REMOVED ACM. FOUND SHAFT DIFFICULT TO TURN. INSTALLED REPAIRED ACM AFTER PRE-LUBING ACM. REINSTALLED DUCTING OPS AND LEAK CHECK DUE OPS AND LEAK CHECK GOOD. WORKED MM 21-51-00.