Explanation: When a RADAR system fails to receive small targets, it indicates a reduction in overall system sensitivity or transmitted power, making weak echoes undetectable. * **Magnetron:** This is the primary high-power RF source for the radar transmitter. A weak or faulty magnetron transmits less power, meaning the echoes returning from targets, especially small ones, will be too weak to be detected. * **IF amplifier:** The Intermediate Frequency amplifier boosts the weak incoming radar echoes after downconversion. If the IF amplifier's gain is reduced or it becomes noisy, the overall sensitivity of the receiver drops significantly, causing small targets to disappear. * **Receiver tuning:** If the receiver (including the local oscillator and IF stages) is not perfectly tuned to the incoming echo frequency, the amplitude of the received signal will be attenuated, reducing sensitivity and making weak returns from small targets undetectable. Options B, C, and D contain components that are less directly related to the fundamental issue of receiving weak signals. For example, processor memory or video processor issues would affect display or data processing *after* reception, not the reception itself. A blown fuse would likely disable a major section entirely, not just cause a loss of small targets. While a power supply issue could cause the problem, option A provides more specific and direct component failures for this particular symptom.