CTS AV System Troubleshooting and Maintenance 5 — Questions and Answers
Question 1: A motorized projection screen stops halfway during deployment and will not respond to further commands. The control relay is confirmed active. What should be checked next?
- Replace the motor drive board
- Inspect the limit switch settings and mechanical travel stops (Correct answer)
- Reprogram the control system trigger voltage
- Verify the projection surface tension
Correct answer: Inspect the limit switch settings and mechanical travel stops
Motorized screens rely on limit switches to define travel endpoints; incorrect calibration or a triggered limit switch mid-travel will halt the motor even with a valid control signal.
Question 2: A Dante audio network shows intermittent dropouts, but only on specific subscriptions. The network switches are unmanaged. What is the recommended corrective action?
- Increase the Dante latency setting to 10 ms or higher for all devices
- Replace unmanaged switches with managed switches and enable QoS/EEE settings appropriate for Dante (Correct answer)
- Reduce the number of Dante channels to below 32
- Switch from unicast to multicast for all subscriptions
Correct answer: Replace unmanaged switches with managed switches and enable QoS/EEE settings appropriate for Dante
Dante requires managed switches with QoS configured and Energy Efficient Ethernet (EEE) disabled; unmanaged switches cannot provide the deterministic latency Dante needs, causing dropouts.
Question 3: An HDMI extender over HDBaseT passes video but produces no audio at the remote display. The source device is confirmed to output audio. What is the most likely cause?
- The HDBaseT cable exceeds the rated distance for audio
- The display's HDMI port does not support ARC
- The EDID from the remote display is not being passed correctly back to the source, causing it to default to a format the display cannot decode (Correct answer)
- The extender's IR passback is blocking the audio return channel
Correct answer: The EDID from the remote display is not being passed correctly back to the source, causing it to default to a format the display cannot decode
HDBaseT extenders can fail to pass EDID correctly, causing the source to output an audio format (e.g., Dolby TrueHD) that the display cannot decode, resulting in silence.
Question 4: A conference room's AV system passes a periodic preventive maintenance (PM) check. Which item is most critical to include in a PM schedule for a high-lamp-hours LCD projector?
- Recalibrate the touch panel annually
- Replace or clean the air filter and log lamp hours against rated lamp life (Correct answer)
- Update the control system firmware quarterly
- Re-terminate all HDMI connections
Correct answer: Replace or clean the air filter and log lamp hours against rated lamp life
Clogged air filters are the leading cause of projector overheating and premature lamp failure, making filter maintenance and lamp-hour tracking the highest-priority PM task for lamp-based projectors.
Question 5: After replacing an amplifier in a 70V distributed audio system, several speakers produce very low volume even at full amplifier output. What is the most likely cause?
- The replacement amplifier has lower output impedance than the original
- The speaker tap transformers are set to a wattage that results in a total load below the amplifier's minimum
- The speaker tap settings are set too high, presenting an impedance that is too low for the amplifier (Correct answer)
- The 70V line has a short circuit between two of the speakers
Correct answer: The speaker tap settings are set too high, presenting an impedance that is too low for the amplifier
In a 70V system, speaker taps set to higher wattage draw more current and reduce the effective impedance; if aggregate tap load drops below the amplifier's minimum impedance, output drops significantly.
Question 6: A technician is troubleshooting a PTZ camera that has lost its preset positions after a power failure. The camera responds to manual pan/tilt/zoom commands. What is the correct resolution?
- Replace the camera's internal battery backup
- Reprogram and save the preset positions in the camera or control system (Correct answer)
- Perform a firmware update to restore preset memory
- Reset the RS-232 baud rate to default
Correct answer: Reprogram and save the preset positions in the camera or control system
PTZ camera presets are stored in volatile or flash memory that may clear on power loss; the correct fix is to reposition the camera and re-save all presets through the control interface.
Question 7: A newly commissioned AV system produces feedback during a speech. The microphone and loudspeaker placement have already been optimized. What is the next recommended step?
- Reduce the main system gain until feedback stops, regardless of intelligibility
- Use a parametric EQ or automatic feedback suppressor to identify and notch the feedback frequency (Correct answer)
- Switch to a cardioid microphone array
- Increase the speaker's crossover frequency
Correct answer: Use a parametric EQ or automatic feedback suppressor to identify and notch the feedback frequency
After optimizing placement, applying a parametric EQ notch filter at the feedback frequency or deploying an automatic feedback suppressor is the standard technique to eliminate feedback while maintaining usable gain.
CTS AV System Troubleshooting and Maintenance 5
A motorized projection screen stops halfway during deployment and will not respond to further commands.
The control relay is confirmed active.
What should be checked next?