CBT - Certified Broadcast Technologist Equipment Troubleshooting and Maintenance Questions and Answers — Questions and Answers
Question 1: A broadcast engineer is troubleshooting a persistent 60 Hz hum in the studio's main audio console. All equipment is powered on, and audio is passing, but the hum is present on all channels. Which of the following is the MOST likely cause of this issue?
- A faulty microphone cable with a broken shield.
- A ground loop caused by multiple ground paths between interconnected equipment. (Correct answer)
- Digital clocking errors between the console and an audio interface.
- Incorrect input gain staging on the console's preamplifiers.
Correct answer: A ground loop caused by multiple ground paths between interconnected equipment.
A 60 Hz hum is the classic symptom of a ground loop. This occurs when audio equipment is connected to ground at multiple points, creating a loop that acts as an antenna for electromagnetic interference from AC power lines. While a faulty cable or incorrect gain staging can cause noise, they are less likely to produce a consistent hum across all channels. Digital clocking errors typically result in clicks, pops, or distorted audio, not a steady hum.
Question 2: When performing maintenance on a high-power FM transmitter, a technician needs to test the transmitter's output stage without broadcasting a signal over the air. Which piece of test equipment is essential for this procedure?
- A spectrum analyzer
- An oscilloscope
- An RF dummy load (Correct answer)
- A field strength meter
Correct answer: An RF dummy load
An RF dummy load is a device that simulates an antenna, allowing a transmitter to be tested at full power without radiating signals. It absorbs the RF energy and converts it to heat. Testing a transmitter without a proper load (like an antenna or a dummy load) can cause the power to be reflected back into the transmitter, potentially causing severe damage. A spectrum analyzer, oscilloscope, or field strength meter are used for measuring signals, but not for safely absorbing the transmitter's full power output.
Question 3: A remote television broadcast is experiencing intermittent video signal loss, presenting as a black screen that comes and goes. The camera, power supply, and recorder have been tested individually and are working correctly. Which of the following is the MOST probable cause to investigate next?
- Incorrect white balance setting on the camera.
- The video format is incompatible with the recorder.
- A damaged or loose BNC or SDI cable connection. (Correct answer)
- Audio levels are clipping in the mixer.
Correct answer: A damaged or loose BNC or SDI cable connection.
Intermittent signal loss, such as a flickering or black screen, is frequently caused by physical connection issues. Damaged cables or loose connectors (like BNC or SDI) can easily lead to a temporary loss of signal continuity. Incorrect white balance would affect color, not the presence of the signal. A format incompatibility or audio clipping would present different symptoms and would likely be consistent, not intermittent.
Question 4: Which of the following is a critical preventive maintenance task for equipment located at a transmitter site to ensure optimal performance and prevent failure?
- Updating the music library on the playout server.
- Regularly cleaning air filters and verifying proper cooling system operation. (Correct answer)
- Calibrating the studio VU meters for accuracy.
- Defragmenting the hard drives on the office computers.
Correct answer: Regularly cleaning air filters and verifying proper cooling system operation.
Transmitter equipment generates a significant amount of heat. Ensuring that cooling systems are functioning correctly by cleaning air filters and checking fans is a crucial preventive maintenance task to prevent overheating and equipment failure. The other options are related to studio or office maintenance and do not directly impact the health and operation of the transmitter equipment itself.
Question 5: A broadcast technician notices that a video feed from a new camera has a slight rolling horizontal bar and distorted picture. The camera is powered from a separate AC circuit than the video switcher it is connected to. What is the most likely solution?
- Replace the camera's lens.
- Adjust the camera's shutter speed.
- Use a ground loop isolator on the video line. (Correct answer)
- Increase the video signal's bit rate.
Correct answer: Use a ground loop isolator on the video line.
The symptoms described, such as rolling bars, are classic indicators of a ground loop in a video system. This often occurs when interconnected equipment is powered from different AC circuits, creating a difference in ground potential. A ground loop isolator is designed to break this DC path for the current, thereby eliminating the interference. Changing the lens, shutter speed, or bit rate would not address the underlying electrical interference issue.
Question 6: During a routine inspection, a technician finds that an audio console is fully powered on, and the meters are active, but no audio is passing to the main outputs or headphones. Which of the following is the FIRST logical troubleshooting step?
- Recalibrate the entire audio console.
- Check if an input source is correctly selected and routed to the main bus. (Correct answer)
- Replace the main power supply unit for the console.
- Reinstall the console's firmware.
Correct answer: Check if an input source is correctly selected and routed to the main bus.
When troubleshooting, it is best to start with the simplest and most common potential issues, often related to operator error or basic signal flow. Verifying that a valid audio source is selected and properly routed to the main outputs is the most fundamental first step. Since the console has power and meters are active, the power supply is likely working. Recalibration and firmware updates are more drastic steps that should only be taken after basic signal path issues have been ruled out.
CBT - Certified Broadcast Technologist Equipment Troubleshooting and Maintenance Questions and Answers
A broadcast engineer is troubleshooting a persistent 60 Hz hum in the studio's main audio console.
All equipment is powered on, and audio is passing, but the hum is present on all channels.
Which of the following is the MOST likely cause of this issue?