What was found
DURING PREFLIGHT, WHEN THE APU WAS STARTED, DISPLAY UNITS 1, 2, & 3 WENT BLANK. THE CARGO FIRE LOWER FWD 1 AGENT DISCHARGED, LIGHT BEGAN FLASHING. THE EAD DISPLAYED VIA 1 FAILURE. QRH FOR CARGO FIRE LWR WAS COMPLIED WITH. IRW 24-20-00 FOUND DURING APU START ACFT WAS ON DIRTY GROUND POWER. AFTER APU START VIA 1 CHECKED NORMAL, AS WELL AS DISPLAYS 1, 2, AND 3.