Gideon Analytical Laboratories performed failure analysis on one Ansul IQ-396X, which was submitted for possible failure due to an electrical surge. These control units have two intelligent signaling line circuits (SLC), 396 intelligent device capacity (198 intelligent detectors and 198 monitors/control modules), four built-in output circuits, up to 64 internal output circuits/relays on optional modules in the unit, 99 programmable zone output relays, and manual sensitivity adjustment.
The CPU 400 unit was dissembled and the entire board and components were inspected under 40x to look for and evidence of EOS (electrical overstress) that may have affected the operation of the unit. No evidence was found. The power rails +5, +24, and ground were checked to ensure the lines were not shorted via a component failure. None were found. Continuity checks were made along the +5, +24 and the ground. No opens were found.
A number of components were checked for operation but could not be checked to see if they meet the manufactures electrical specification sheet because they reside on the board. There are a number of General Semiconductor diodes for voltage transient protection and clamping for I/O data lines. The diodes operated. The Infineon processor was checked to see if a surge hit it. The data lines showed the typical diode trace with no shorts to ground.
Since we did not have schematics, Gideon recommended that it would be best to send the unit back and test software integrity within the CPU-400 without a reload. This could possibly be done using the Verifire off-line programming and test utility explained in the Ansul literature. If the software integrity passes, then functional testing the unit under the same environmental conditions to determine if there is a temperature, humidity, or placement induced the failure mode condition preexisting.
Failure analysis provided by Gideon Analytical Laboratories cannot only explain where a problem arises but also where a problem does not arise. If you are testing or qualifying a PCB, call Gideon Analytical Laboratories.