What was found
CREW ATTEMPTED TO DISCHARGE APU FIRE BOTTLE. FIRE BOTTLE DID NOT DISCHARGE. (VERIFIED IN ROA ON 2 OCT 07). VERIFIED 28 VOLTS AT SQUIB CONNECTOR. REPLACED SQUIB AS PRECAUTION. OPS CHECKED OLD SQUIB, CHECKED GOOD. SUSPECT FAULT CAUSED BY APU AIR/GROUND RELAY 7615-K4 WHICH IS ENERGIZED BY RT MAIN BUS, DE-ENERGIZED WHEN APU GENERATOR CONTACTOR FAILED CAUSING LARGE BUSS VOLTAGE DROP TAKING POWER FROM SQUIB CARTRIDGE. REMOVED AND REPLACED RELAY 7615-K4 AS PRECAUTION.