When loose oxide builds up in the tape path, it can travel with the tape to the drum assembly and prevent the video head from making contact with the tape. The result is a heavily obscured image or a complete loss of image. A video head clog requires thorough cleaning of the video heads if the clog obstructs RF completely during playback. In most cases, a severe head clog cannot be removed by playing a cleaning tape through the VTR. The head and drum assembly must be manually cleaned using a cleaning solution.
Can it be fixed?
Yes: stop playback and clean the video heads on the the player using an appropriate solvent and cotton swab. While you are at it, clean the tape path to prevent possible recontamination.