What was found
CLT - FLT 299 - ON CLIMB-OUT FROM CLT, AT FL210, THE NR 1 ENGINE N1 INDICATOR BEGAN FLUCTUATING IN ALL PARAMETERS OF FLIGHT. THE N1 WOULD SURGE PLUS OR MINUS 7 PERCENT EVERY 7 TO 10 SECONDS. FLIGHT RETURNED TO FIELD AT CLT AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE REMOVED AND REPLACED THE NR 1 ENGINE MAIN ENGINE CONTROL. PERFORMED ENGINE RUN. OPERATIONAL CHECK AND LEAK CHECK GOOD. (M)