Explanation: A Phase Locked Loop (PLL) is a feedback control system that generates a stable output frequency by constantly comparing it to a reference. The Voltage Controlled Oscillator (VCO) is the core component within the PLL that *generates* this output frequency. Its oscillation frequency is directly controlled by a voltage from the loop filter, which in turn reflects the phase difference detected. If the VCO is inoperative, it cannot produce any oscillations, fundamentally breaking the PLL's ability to generate or lock onto a frequency. The AGC circuit controls receiver gain, the Beat Frequency Oscillator (BFO) is used for SSB/CW demodulation, and an IF filter shapes the intermediate frequency bandwidth. These components are external to or peripheral to the PLL's primary function of frequency generation and control; their failure would not directly cause the PLL itself to be inoperative.