As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INADVERTENTLY A TECHNICIAN INSTALLED A CRJ700 DCU IN A CRJ200 AND DAMAGED THE DCU. INSPECTED DCU2 RACK CONNECTION AND WIRING AS REQUIRED. NO DEFECTS NOTED. INTERNAL CORRECTIVE ACTION, EA IMPLEMENTED TO INSTALL POLORIZING KEYS IN ALL CRJ200 AIRCRAFT DCU MOUNTING RACKS.