C7 Troubleshooting & Maintenance Procedures 3

Question 1

A technician is called to troubleshoot a telecom system where analog phone lines have loud hum on all circuits. What is the MOST likely cause?

Accepted Answer

Ground loop induced 60 Hz interference

Answer

A 60 Hz hum on all analog lines simultaneously is a classic symptom of a ground loop, where differing ground potentials create a current in the signal path.

Question 2

When performing preventive maintenance on a fiber optic network, a technician should clean connectors with:

Accepted Answer

Isopropyl alcohol and a lint-free wipe, then inspect with a fiber scope

Answer

Proper fiber connector cleaning uses IPA with lint-free wipes followed by inspection with a fiber scope to confirm no contamination remains.

Question 3

A technician measures a network cable and finds the propagation delay skew between pairs exceeds TIA-568 limits. This will MOST likely cause problems with:

Accepted Answer

MIMO signal processing that relies on pair timing

Answer

Excessive delay skew affects systems like Gigabit Ethernet that use all four pairs simultaneously and rely on timed arrival of signals from each pair.

Question 4

A card reader at an exterior door grants access intermittently in cold weather. After ruling out software issues, the MOST likely hardware cause is:

Accepted Answer

The door contact is misaligned due to frame thermal contraction

Answer

Metal door frames contract in cold weather, which can misalign magnetic door contacts or latch sensors and cause intermittent status reporting to the controller.

Question 5

During a fire alarm panel maintenance inspection, the technician notices the battery float voltage reads 25.5V on a 24V nominal system. This indicates:

Accepted Answer

Normal float charging voltage for a sealed lead-acid battery

Answer

A float voltage of approximately 13.5–13.8V per 12V battery (27–27.6V for 24V systems) is normal; 25.5V is within normal range for a properly maintained sealed lead-acid battery.

(C7) California C7 Low Voltage Systems Contractor Certification Practice Test

(C7) California C7 Low Voltage Systems Contractor Certification Practice Test

C7 Troubleshooting & Maintenance Procedures 3