Start with a safe incident record
Record the intersection, approach, time, weather, signal group, controller alarm and the exact symptom before opening a cabinet. Secure the work area and follow the project isolation procedure. A clear record prevents a temporary communication fault from being mistaken for a failed signal head.
Use the symptom to narrow the search
| Symptom | First checks | Likely areas |
|---|---|---|
| Entire head dark | Cabinet output, fuse, connector seating | Power feed, harness, module |
| One colour dark | Output channel and colour lead | LED module, terminal, cable |
| Flicker or drop-out | Voltage under load, moisture, vibration | Loose crimp, water ingress, driver |
| Wrong indication | Phase mapping and terminal labels | Controller configuration or wiring |
Check power and controller interfaces
Compare the measured supply and output with the approved project values, not a generic nominal value. Confirm the controller phase plan, channel assignment, flash-transfer relay and conflict monitor status. If the controller is healthy, isolate the field cable and test the circuit in sections.
Inspect the field harness and signal head
Look for crushed cable, loose terminals, corrosion, damaged glands and connectors that are not fully locked. Check for a drip loop and strain relief. Inside the head, inspect the module, lens, visor and seals for heat damage or condensation. Replace only the failed subassembly and preserve the removed part for analysis.
Close the job with an acceptance checklist
- Restore every colour and arrow/figure indication in the approved sequence.
- Confirm night dimming, flash mode and controller conflict monitoring.
- Photograph the repaired termination and record measured values.
- Update the spare-parts and maintenance log for the next visit.
When to request a configuration review
Escalate when the fault follows a controller change, a new cabinet, a tunnel interface or a non-standard indication. GAOQIAO can review the controller arrangement, signal head configuration and wiring information before a replacement is selected.
FAQs
Should I replace the whole signal head when one colour fails?
Usually no. Test the channel, harness and LED module first; replace the smallest failed assembly that meets the project requirements.
Why does a fault disappear after rain?
Intermittent moisture at a gland, connector or terminal can dry out and temporarily restore contact. Record the condition and inspect seals before it returns.