If range rings on a PPI indicator are oval in shape, which circuit might be faulty?

When range rings on a Plan Position Indicator (PPI) appear oval instead of circular, it typically indicates a problem with the sweep generation circuit. This circuit is responsible for controlling the timing and shape of the radar's sweep across the display.

An oval shape suggests that the sweep is not being generated correctly, possibly due to issues like incorrect timing or synchronization, which affects the uniformity of the scan. The expected result of a properly functioning sweep generation circuit is circular range rings, as the radar should scan evenly around the display.

The other circuits listed can cause different types of issues but would not specifically lead to oval range rings. For example, a timing circuit might affect the timing of the system but wouldn't necessarily distort the shape of the rings. Similarly, while a video amplifier circuit may impact the quality of the signal displayed, it wouldn’t alter the geometric characteristics of range rings. The range marker circuit primarily deals with the indication of range rather than the shape of the radar sweep.

Therefore, the correct inference is that a fault in the sweep generation circuit would directly lead to deformed range rings, such as those appearing oval on the PPI display.