As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON ENTERING THE AIRPLANE BEFORE REPOWERING THE AIRPLANE THERE WAS MODERATE ACIDIC BURING SMELL THROUGHOUT THE AIRPLANE. REMOVED FROM SERVICE. PERFORMED FIM TASK 21-20-00-810-801-A REF PREV LOGPAGE FOR LH RECIRC FAN CB FOUND TRIPPED AND DEFERRAL OF SYSTEM. PILOT COMPLETED M-744. SMELL NO LONGER PRESENT IN CABIN. NO PARTS REPLACED. RETURNED TO SERVICE.