What was found
RECEIVED MAIN CARGO DOOR ALERT AT FL 390. QRH WAS FOLLOWED AND DIVERTED TO KJAX. NO PRESSURIZATION ISSUES WERE NOTED AT ANY TIME. ALERT WENT AWAY ON DESCENT PASSING FL 240. REVERSED MEL 52-71-01-02. RE-PERFORMED CARGO DOOR PROX TEST REF FIM 52-71-809 AND FIM 32-09-00/101 FIG 103. CONFIRMED INTERMITTENT FAILURE OF A4 LOGIC CARD POSITION 4. REMOVED & REPLACED PSEU A4 POS 4 LOGIC CARD REF AMM 31-70-03-4-99. ELDEC P/N 8-535-04. S/N OFF D14732. S/N ON D8653. RE-PREFORMED MAIN CARGO DOOR INDICATION TEST I.A.W. FIM 52-71 FAULT TREE 809 AND FIM 32-09-00/101