What was found
EN ROUTE, CREW NOTICED AN ELECTRICAL BURNING ODOR & SMOKE IN COCKPIT. FLT TERMINATED & AN UNEVENTFULL LANDING MADE. MX INVESTIGATION REVEALED THE NR 2 RADIO CRATE COOLING FAN SMOKE BLACKENED & DIFFICULT TO TURN BY HAND. FAN REMOVED & BENCH TESTED. DURING BENCH TEST FAN ROTATED VERY SLOWLY & OVERHEATED. NOTED DURING TEST THE CURRENT DRAW BY FAN LESS THAT 15 AMPS, WHICH WOULD EXPLAIN WHY ASSOCIATED ACFT 15 AMP C/B DID NOT TRIP. FAN REPLACED. ASSOCIATED WIRING HARNESSES & C/BS INSPECTED & TESTED. COOLING FAN INSTALLATION FUNCTION TESTED ON THE AIRCRAFT AND SHOWED NO EVIDENCE OF DEFECTS. THE AIRCRAFT RELEASED TO SERVICE.