Testing, Troubleshooting, and Maintenance
What this domain tests
This domain tests systematic fault finding, test equipment use, baseline measurements, and preventive maintenance. Expect items on signal flow, EDID/HDCP failures, audio hum, network faults, and how to isolate a problem without changing multiple variables at once.
Core rules
- Troubleshoot by signal flow: source → transport → processing → display or loudspeaker. Substitute a known-good source or display to bisect the fault.
- Use the right instrument: multimeter for power and continuity, cable tester for pinout, audio analyzer for level and distortion, and video test generator for format checks.
- Record baselines: gain structure, delay, EQ, IP addresses, firmware versions, and measured SPL or light output.
- Many “no video” faults are EDID or HDCP negotiation failures, not bad cables; check source resolution, display capability, and repeater compatibility.
- Preventive maintenance includes cleaning filters and vents, checking terminations, verifying backups, and reviewing logs.
Worked example
A room has a 60 Hz hum in the audio system. You find the hum remains when the source is disconnected but disappears when the amplifier input is terminated with a shorting plug. What is the likely cause and next step?
- The hum is entering the amplifier input path, not the power supply or loudspeaker.
- A shorting plug removes the input signal and its ground loop; the remaining hum indicates an input wiring or grounding issue.
- Next, inspect the input cable, connector shield, and ground connections; test with a known-good balanced cable and avoid lifting safety grounds. Reasoning: isolate by substitution and do not “fix” a ground loop by removing a protective earth.
Traps
- Changing several variables at once, which destroys diagnostic information.
- Assuming every HDMI failure is a cable; EDID and HDCP are common causes.
- Lifting the safety ground to cure hum.
- Skipping baseline records, so later faults cannot be compared.
- Ignoring firmware and configuration drift in maintenance.