C7 Troubleshooting & Maintenance Procedures 2 — Questions and Answers
Question 1: A security camera system shows intermittent video loss only during afternoon hours. What is the MOST likely cause?
- Faulty DVR hard drive
- Thermal expansion causing loose coaxial connections (Correct answer)
- Incorrect camera resolution setting
- Outdated firmware on the NVR
Correct answer: Thermal expansion causing loose coaxial connections
Intermittent faults that occur during the hottest part of the day are often caused by thermal expansion loosening coaxial or other connectors.
Question 2: When testing a fire alarm circuit, a technician measures 0 ohms resistance between the positive and negative conductors. This indicates:
- Normal end-of-line resistor reading
- An open circuit fault
- A ground fault
- A short circuit fault (Correct answer)
Correct answer: A short circuit fault
Zero ohms between positive and negative conductors indicates a short circuit, where current bypasses the intended load path.
Question 3: Which tool is MOST appropriate for locating a break in a buried low-voltage cable without excavation?
- Megohmmeter
- Time-domain reflectometer (TDR) (Correct answer)
- Clamp-style ammeter
- Digital multimeter
Correct answer: Time-domain reflectometer (TDR)
A TDR sends a pulse down a cable and measures the time for the reflection to return, pinpointing the location of breaks or impedance changes.
Question 4: A nurse call system annunciator displays a fault for Room 312, but staff confirm no call was made. The FIRST diagnostic step should be:
- Replace the annunciator panel
- Inspect the Room 312 call station for a stuck or shorted button (Correct answer)
- Rewire the entire zone
- Update the software on the master station
Correct answer: Inspect the Room 312 call station for a stuck or shorted button
A phantom activation most commonly results from a mechanically stuck or electrically shorted call button at the originating station.
Question 5: During a CCTV system inspection, the technician notices the image on a PTZ camera has excessive noise in low-light conditions. The BEST corrective action is to:
- Increase the camera's gain setting (Correct answer)
- Replace the coaxial cable with Cat6
- Adjust the iris to fully closed
- Set the white balance to manual mode
Correct answer: Increase the camera's gain setting
Increasing the gain amplifies the sensor signal in low-light conditions, reducing apparent noise at the cost of some image quality.
Question 6: A structured cabling technician finds that a newly terminated Cat6 link passes all pair tests but fails the alien crosstalk (ANEXT) test. The MOST likely cause is:
- Incorrect cable category installed
- Excessive untwisting of pairs during termination (Correct answer)
- Missing cable shield
- Wrong punch-down tool blade used
Correct answer: Excessive untwisting of pairs during termination
Excessive untwisting of pairs at termination points increases susceptibility to alien crosstalk between adjacent cables.
Question 7: A building's access control system fails to grant entry after a power outage is restored. The most probable cause is:
- The door lock solenoid burned out during the outage
- The controller lost its database and needs re-programming
- The backup battery did not maintain controller memory (Correct answer)
- All credential cards were deactivated by the power surge
Correct answer: The backup battery did not maintain controller memory
If the backup battery fails or is depleted, controller memory (including door schedules and user credentials) may be lost when main power is removed.
C7 Troubleshooting & Maintenance Procedures 2
A security camera system shows intermittent video loss only during afternoon hours.
What is the MOST likely cause?