Ryzen 5 5600X B450 Motherboard No Display CPU Debug LED: BIOS Update Required
A technician is building a new desktop computer using an AMD Ryzen 5 5600X CPU and a B450 chipset motherboard. After assembling all components, the system powers on. The case fans and CPU fan spin, but there is no display output. The motherboard's CPU debug LED remains lit. The technician has already reseated the CPU (no bent pins), verified the RAM is seated correctly, and tested the power supply with a multimeter (voltages within specification). The GPU works in another system. Which of the following should the technician do NEXT?
Quick Answer
The answer is to update the motherboard BIOS to a version that supports Ryzen 5000 series processors. This is correct because the Ryzen 5 5600X is a Zen 3 architecture CPU, while B450 motherboards originally shipped with BIOS firmware only compatible with older Ryzen 2000 and 3000 chips. Without a BIOS update containing the necessary AGESA microcode, the motherboard cannot recognize or initialize the CPU, causing the CPU debug LED to stay lit and no display output—even when all other components are verified working. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your understanding of CPU and motherboard compatibility, specifically that chipset support can lag behind newer processor generations. A common trap is to suspect a faulty CPU or PSU, but the spinning fans and working GPU point squarely to a firmware mismatch. Memory tip: “5000 series needs a BIOS that’s current—if the CPU LED glows, the BIOS must go.”
⚠ Common exam trap
The trap here is that candidates see a working GPU and power supply and assume the issue is a faulty component or connection, overlooking the critical motherboard-CPU compatibility requirement that is unique to AMD's AM4 platform evolution.
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
✓
Update the motherboard BIOS to a version that supports Ryzen 5000 series processors
The AMD Ryzen 5 5600X is a Vermeer (Zen 3) processor, while B450 motherboards originally launched with support for Ryzen 2000 (Pinnacle Ridge) and Ryzen 3000 (Matisse) CPUs. A BIOS update is required to add the AGESA microcode that enables Zen 3 support. The CPU debug LED staying lit indicates the motherboard cannot initialize the CPU, which is the classic symptom of an incompatible BIOS version.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Update the motherboard BIOS to a version that supports Ryzen 5000 series processors
Why this is correct
B450 boards shipped before Ryzen 5000 existed, so their factory BIOS lacks the required AGESA microcode; the lit CPU debug LED with spinning fans confirms the CPU cannot initialise. Flashing a compatible BIOS version adds that support, resolving the no-POST condition without replacing hardware.
- ✗
Replace the power supply unit with a higher wattage model
Why it's wrong here
The multimeter already confirmed the PSU's rails are within specification, so wattage cannot explain the lit CPU debug LED. Higher-wattage units address total load headroom for multi-GPU or high-TDP builds, not a B450 board refusing to POST with a 5600X.
- ✗
Reseat the GPU in a different PCIe slot
Why it's wrong here
The GPU is verified working in another system, and a lit CPU debug LED indicates the board halts before PCIe initialisation, so slot changes cannot clear it. Reseating the GPU addresses physical slot or riser faults causing no display with a normal POST.
- ✗
Replace the CMOS battery and clear the CMOS
Why it's wrong here
A lit CPU debug LED with spinning fans points to CPU incompatibility or firmware, not CMOS corruption; clearing CMOS cannot add Ryzen 5000 support to a B450 board. Replacing the battery is right when settings fail to persist or the clock resets.
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. 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?
medium- A.The CPU is not receiving sufficient voltage from the power supply.
- ✓ B.The B450 motherboard requires a BIOS update to be compatible with the Ryzen 5 5600X.
- C.The CPU is defective and needs to be replaced.
- D.The RAM is not installed in the correct slots for dual-channel memory.
Why B: 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.