How can video hum be visually identified?

Video hum can be visually identified by observing horizontal bars that appear to roll from the bottom to the top of the screen. This phenomenon often occurs because of interference, typically from electrical sources, which disrupts the video signal. This interference manifests as a noticeable pattern of lines that move vertically across the display, creating an unsettling visual effect.

The presence of these rolling bars is a clear indicator of hum, suggesting that there is an issue with the synchronization of the video signal, which could be caused by improper grounding or poor connections in the video distribution system. Identifying this specific symptom is crucial for a technician because it helps in diagnosing potential electrical problems and correcting them to restore a clear and stable video output.