When the center of a CRT shows no target video that shrinks with increased range scale, which area is likely defective?

In the context of a CRT (Cathode Ray Tube) display, when the center shows no target video that shrinks with an increased range scale, this suggests a specific issue related to the processing of video signals. The TR (Triggering) cell plays a critical role in generating and stabilizing the display of signals on the CRT.

A malfunction in the TR cell can prevent the video display from being properly triggered and presented on the screen. When the video signals are not being correctly processed or when the trigger is faulty, the result can often be a lack of a visible target in the center of the screen, which may become more pronounced as the range scale is adjusted.

An adjustment of the range scale typically changes how signals are processed, and if the triggering mechanism isn't functioning correctly, the result will be an absence of stable video in the expected display area. This explains why the TR cell is the most likely defective component in this scenario. The other areas, while potentially faulty in other contexts, do not directly correlate to the symptoms described in this situation.