220-1101 Hardware Practice Question
A technician is troubleshooting a desktop computer that will not boot. The motherboard has a 7-segment debug LED that displays code '55'. According to the motherboard manual, this code indicates a memory initialization error. The technician has already reseated the RAM, tested each stick individually in different slots, and replaced the RAM modules with known good ones. The computer still displays the same code. Which of the following components is the MOST likely cause of the issue?
⚠ Common exam trap
It's easy for candidates to assume the debug LED code '55' always points to the RAM modules themselves, overlooking that the CPU's integrated memory controller is the actual component that initializes the memory.
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 CPU is faulty or has bent pins
The motherboard debug LED code '55' specifically indicates a memory initialization error. Since the technician has already reseated, swapped slots, and replaced the RAM with known good modules, the issue is not with the RAM itself. The memory controller is integrated into the CPU (since Intel Nehalem and AMD K8), so a faulty CPU or bent pins on the CPU/socket can prevent the memory controller from initializing RAM, causing this persistent code.
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 motherboard is defective
Why it's wrong here
The motherboard is not the first suspect because modern CPUs have the memory controller on the die. While a defective motherboard (damaged traces, bad slots, VRM issues) could cause memory errors, the CPU's physical/electrical integrity is more likely and easier to check. A technician would typically reseat or replace the CPU before condemning the motherboard. Additionally, a bad motherboard often presents with broader symptoms like no power or multiple device failures, not a clean memory-specific error.
When this WOULD be correct
A motherboard debug LED shows a code indicating a memory error, and the technician has verified the CPU is functional (e.g., tested in another board) and RAM is known good. In that scenario, the motherboard itself is the most likely cause.
- ✓
The CPU is faulty or has bent pins
Why this is correct
The memory controller is physically located on the CPU die. A faulty CPU or bent pins on the socket (or CPU) can break the memory bus, preventing the CPU from communicating with the RAM even if the DIMMs are known to be good. POST memory initialization relies on the CPU's integrated memory controller to read SPD and train the DIMMs; any failure here produces a memory error beep code.
- ✗
The power supply is not delivering adequate voltage to the RAM slots
Why it's wrong here
RAM slots are not powered directly from the power supply; they receive a low-voltage rail (e.g., 1.2V for DDR4) generated by the motherboard's VRM from the 12V supply. If the PSU was underperforming, the system would likely fail to power on, reset, or shut down under load, not produce a discrete memory error code. The fact that the system reaches memory initialization means the main rails and motherboard power regulation are functioning. Therefore, a PSU deficiency is an unlikely cause for this specific error.
When this WOULD be correct
A computer randomly freezes or fails to boot with RAM-related errors, and a multimeter shows voltage at the RAM slots is below specification (e.g., 1.2V for DDR4 instead of 1.35V). Replacing the power supply resolves the issue, confirming inadequate voltage to RAM.
- ✗
The CMOS battery needs to be replaced
Why it's wrong here
A depleted CMOS battery only causes loss of the BIOS configuration settings (such as boot order and memory timings) and resets the clock. It does not affect the CPU's integrated memory controller or the voltage to RAM; the system would still attempt to power on, run POST, and train DRAM. In fact, most systems will boot with a dead battery aside from BIOS reset and time errors. Therefore, it cannot be the root cause of a memory initialization failure.
When this WOULD be correct
A computer fails to boot and displays 'CMOS checksum error' or 'Time/Date not set'. Replacing the CMOS battery resolves the issue, as the battery powers the CMOS memory that stores BIOS settings.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The CPU is faulty or has bent pinsCorrect answer▾
Why this is correct
The memory controller is physically located on the CPU die. A faulty CPU or bent pins on the socket (or CPU) can break the memory bus, preventing the CPU from communicating with the RAM even if the DIMMs are known to be good. POST memory initialization relies on the CPU's integrated memory controller to read SPD and train the DIMMs; any failure here produces a memory error beep code.
✗The motherboard is defectiveWrong answer — click to see why▾
Why this is wrong here
The technician has already reseated RAM, tested sticks individually, and replaced with known good modules, yet the error persists. A defective motherboard could cause memory errors, but the debug LED code '55' specifically indicates memory initialization, which is often tied to the CPU's memory controller. Since RAM has been ruled out, the CPU is more likely the culprit.
★ When this WOULD be the correct answer
A motherboard debug LED shows a code indicating a memory error, and the technician has verified the CPU is functional (e.g., tested in another board) and RAM is known good. In that scenario, the motherboard itself is the most likely cause.
Why candidates choose this
Candidates may assume that after eliminating RAM, the motherboard is the next likely component, overlooking that the CPU contains the memory controller and can cause memory initialization errors.
✗The power supply is not delivering adequate voltage to the RAM slotsWrong answer — click to see why▾
Why this is wrong here
The power supply delivering inadequate voltage to RAM slots would typically cause intermittent errors or system instability, not a consistent memory initialization error code after RAM has been replaced and tested individually. The debug code '55' persists despite known-good RAM, pointing to a CPU or motherboard issue, not power delivery.
★ When this WOULD be the correct answer
A computer randomly freezes or fails to boot with RAM-related errors, and a multimeter shows voltage at the RAM slots is below specification (e.g., 1.2V for DDR4 instead of 1.35V). Replacing the power supply resolves the issue, confirming inadequate voltage to RAM.
Why candidates choose this
Candidates may think that power supply issues can cause memory errors because RAM requires stable power, and they might overlook that the CPU's memory controller is a more direct cause when RAM itself is verified good.
✗The CMOS battery needs to be replacedWrong answer — click to see why▾
Why this is wrong here
A dead CMOS battery causes time/date resets and BIOS settings loss, not a memory initialization error code 55. The error persists after RAM replacement, so the battery is irrelevant.
★ When this WOULD be the correct answer
A computer fails to boot and displays 'CMOS checksum error' or 'Time/Date not set'. Replacing the CMOS battery resolves the issue, as the battery powers the CMOS memory that stores BIOS settings.
Why candidates choose this
Candidates may confuse CMOS battery failure with boot issues, thinking it can cause memory errors, or they may recall that CMOS issues can prevent booting in some cases.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
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RAM Error Types: ECC vs Non-ECC
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
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.
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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.