What was found
NORMAL TAKEOFF THRUST SET N1 100.1/OAT AND 03.*C WITH AUTOTHROTTLES ON AT 1500. AGL JUST AFTER CLIMB, THRUST SET TO 102.5, NR 4 ENGINE EXPERIENCED A MASSIVE COMPRESSOR STALL AT 2800, MSL. IMMEDIATELY REDUCED THRUST TO NR 4 ENGINE. STALL CEASED AT THAT TIME. IT WAS NOTED THAT NR 4 EGT WAS RAPIDLY CLIMBING IN THE CAUTION RANGE BUT RECOVERED WHEN THRUST WAS REDUCED TO IDLE. KEPT NR 4 ENGINE AT IDLE RPM AND RETURNED TO AIR FIELD. REMOVED AND REPLACED NR 4 ENGINE PER W/O 01-AA-45. OPS CHECK OK PERFORMED TEST ON NR 4 AND CHECK OK.