Maintenance, Troubleshooting, and Inspection
Maintenance and troubleshooting questions are diagnostic: given a symptom, what do you test first? Build a mental ladder from power to field. Cabinet side: incoming voltage, main breaker, surge arrestor, power supply, controller, conflict monitor, load switches, terminal blocks. Field side: wiring, signal heads, detectors.
Flashing operation is the classic trap. A signal flashing yellow/red may be in controller-directed flash or in conflict flash commanded by the conflict monitor (MMU). Controller flash is a normal mode; conflict flash signals a fault such as a conflicting green, a shorted load switch, or a failed field wire. Download the MMU event log before clearing it - clearing destroys your evidence. Then check the indicated channel: an open field wire looks different from a shorted display.
Detector problems: an inductive loop reading far below its design inductance has shorted turns; one reading high or unstable may have a poor splice or moisture intrusion. Pull-test splices and check loop lead-in twists. LED failures are usually a module or driver rather than a whole head; verify controller output before replacing a head.
Inspection: use a written checklist, record measurements, and photograph deficiencies. Confirm torque values, bonding continuity, battery backup function, and that as-built documentation matches the timing and phasing actually running.
Rule of thumb: after any repair that changes field wiring, re-run a functional test of every phase and re-verify conflict monitor operation before restoring coordination.