CHASE IOLAN: MAC ADRESS CORRUPTION

16 PORT CHASE IOLAN TERMINAL SERVER, WITH VDU’S AND SERIAL PRINTERS CONNECTED. HOST IS A HP UNIX BOX.
FOR SOME REASON THE LAST 3 OCTETS OF THE MAC ADRESS DEFAULT TO ZERO, NOW AND AGAIAN.
UNIT HAS BEEN CHANGED 3 TIMES AND A MAINS ANALYZER SHOWS NO PROBLEMS, CONNECTED TO A HUB WHICH HAS BEEN CHANGED VIA RJ45-10BASE-T.
CABLE ALSO CHANGED. SECURE ROOT PASSWORD. IMPOSSIBLE TO ISOLATE DEVICES CONNECTED AS VERY INTERMITTENT.ANY IDEAS, THANKS IN ANTICIPATION