What was found
(CAN) AFTER CUSTOMER COMPLAINED OF OSCILLATION IN COMPASS CARD OF EHSI, DETERMINED THAT PROBLEM CAUSED BY VOLTAGE FLUX OF NR 1 AC BUS. TROUBLESHOOTING REVEALED THAT VOLTAGE FLUX ONLY PRESENT WHEN INVERTER OPERATED AT APPROXIMATELY 12 TO 20 PERCENT OF FULL LOAD. IT ALSO FOUND THAT BOTH INVERTERS ON A/C PRESENTED SAME PROBLEM. INVERTERS ARE MARATHON POWER TECHNOLOGIES MODEL PC-250, SER-NO 4343&4346. BOTH INVERTS ARE AT MOD LEVEL C. WHEN INVERTS W/O MOD C WERE INST IN A/C PROBLEM NO LONGER PRESENT.