What was found
SMOKE COMING FROM THE AVIONICS BAY ON FLIGHT 3306. MAINTENANCE REPLACED AVIONIC VENT FAN P/N M4401D8A, S/N OFF 598, S/N ON 576 REF: AMM 21-23-10-2. NO FIX. FOUND WHITE SMOKE COMING FROM SUPPLEMENTAL A/C SYSTEM UNDER THE FLOOR AND OUT THE AVIONICS RACK. DEFERRED SUPPLEMENTAL A/C SYSTEM PER MEL 21-50-2 (D) ENTERED INTO DMR, MXC NOTIFIED SUPPLEMENTAL A/C SYS PER MEL 21-50-2 (D) ENTERED INTO DRM, MXC NOTIFIED 0782. C/W MAINTENANCE PROCEDURES. REMOVED AND REPLACED COMPRESSOR MOTOR.