OK. It could be the NAC. The strobe is charging as long as there is power on the circuit. The strobe flashes when the power to the NAC is shut off for about 20 milliseconds. Try switching the programming and the devices between the NACs. If NAC1 is the QALERT change it to NAC2 and test it. Maybe the NAC you are using is not inserting the sync pulses correctly. Does the strobe flash at all? Like one flash when the system completes a reset?