Fault Isolation: No Video, No Audio, Echo, Network Dropout, Failed Controls

Est. 60 minCompetency: Isolate the classic AV field faults methodically.

Learning objectives

Isolate no-video faults through the video path.
Isolate no-audio and echo faults through the audio path.
Isolate network dropouts and failed controls.
Use a signal-tracing method.

Lesson content

Field faults fall into a few patterns. Trace the affected path from source to output and you find the break quickly. Guessing replaces itself; tracing ends the fault.

No video

1Confirm the source is outputting (laptop display, source LED).
2Confirm the cable and connector at the source.
3Confirm the switcher received and routed it (status, correct input).
4Confirm the display is on and on the right input.
5Swap a known-good cable; isolate to source, transport, switcher, or display.

No audio

1Trace the audio path: mic → preamp → DSP → amp → speaker.
2Check mute and routing in the DSP.
3Confirm the amp is on and the speaker is connected.
4Tap the mic stage by stage with headphones or a meter to find where it dies.

Echo (far end hears itself)

AEC not enabled, or the reference is wrong/missing.
Room speakers too loud for AEC to converge.
Mic picking up a reflection the AEC cannot model.
Verify AEC per mic and the reference; lower room level; recheck.

Network dropout / failed control

Ping the device; check link LED and PoE.
Check the IP schedule for a duplicate or wrong VLAN.
Check the control link (serial/IP) and the driver's command/response.
Read the logs for timeouts; isolate to cable, switch, addressing, or device.

One change at a time

Change one thing, then test. Changing three things at once 'fixes' the fault and hides the cause, guaranteeing it returns. Trace, change, test, repeat.

Worked example

No video on the right display: source outputting, cable good at the source, switcher shows the route to output 2, but the display is on input 1. Set the display to input 2 — video appears. The fault was the display's input selection, not the AV system.

Implementation checklist

✓Fault traced source-to-output along the affected path.
✓One change made, then tested.
✓Audio path traced stage by stage for no-audio.
✓AEC reference and room level checked for echo.
✓Logs read for network/control faults.

Downloadable study guide

study-guide.txtcopy-paste ready

01. No video: trace source→cable→switcher→display; swap a known-good cable.
02. No audio: trace mic→preamp→DSP→amp→speaker stage by stage.
03. Echo: AEC not enabled/wrong reference, or room too loud; verify per mic.
04. Network/control: ping, link/PoE, IP schedule, logs; one change at a time.