220-1101 Hardware Practice Question
A technician is building a new desktop computer with an AMD Ryzen 5 5600X CPU and a B450 chipset motherboard. The system powers on, case fans spin, and the CPU fan spins, but there is no display output and no POST beeps. The motherboard's CPU debug LED remains lit. The technician has already reseated the CPU (no bent pins), verified the RAM is compatible and seated correctly, and tested the power supply with a multimeter (voltages within spec). Which of the following is the MOST likely cause?
⚠ Common exam trap
It's easy for candidates to assume all AM4 CPUs are interchangeable on any AM4 motherboard, overlooking the critical BIOS version dependency between chipset generation and CPU architecture.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The B450 motherboard requires a BIOS update to be compatible with the Ryzen 5 5600X.
The Ryzen 5 5600X is based on the Zen 3 architecture, while B450 motherboards were originally designed for Zen+ and Zen 2 CPUs. Without a BIOS update that includes AGESA firmware supporting Vermeer (Zen 3), the motherboard cannot initialize the CPU, causing the CPU debug LED to stay lit and preventing POST. The technician has already verified power, RAM, and CPU seating, making an incompatible BIOS the most likely cause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The CPU is not receiving sufficient voltage from the power supply.
Why it's wrong here
This is incorrect because the power supply voltages were verified with a multimeter and are within ATX specifications, confirming the PSU is healthy. The CPU fan spinning also demonstrates that the motherboard is delivering standby power and that the power delivery circuit is operational. Insufficient Vcore would typically cause an immediate shutdown, failure to spin fans, or a power-related debug LED, not a CPU LED error. On a B450 board with a Ryzen 5 5600X, a CPU LED during POST is the textbook symptom of missing BIOS microcode for Zen 3, making BIOS incompatibility the far more probable cause.
- ✓
The B450 motherboard requires a BIOS update to be compatible with the Ryzen 5 5600X.
Why this is correct
B450 motherboards lack native support for Zen 3 CPUs. A BIOS update (often labeled 'Ryzen 3000/5000 ready') is needed to add the microcode for the 5600X. Without it, the CPU will not be recognized, causing a no-POST condition with a CPU LED error.
- ✗
The CPU is defective and needs to be replaced.
Why it's wrong here
A defective CPU is possible, but a BIOS incompatibility is a much more common and likely issue given the known need for updates on B450 boards. The technician should rule out the BIOS first before concluding the CPU is faulty.
- ✗
The RAM is not installed in the correct slots for dual-channel memory.
Why it's wrong here
Incorrect RAM slot placement could cause a no-boot, but the debug LED is a CPU LED, not a DRAM LED. The technician already verified RAM compatibility and seating, and a slot issue would typically show a DRAM LED.
Go deeper
Related to this question
Learn chapter
GPUs and Display Technologies
Key term
Light-emitting Diode
A light-emitting diode (LED) is a semiconductor device that emits light when an electric current passes through it, commonly used as an indicator or illumination source in electronic devices.
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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