easyMultiple ChoiceObjective-mapped
220-1201 Practice Question: A customer reports that their desktop computer…
A customer reports that their desktop computer randomly shuts down after a few minutes of gaming, but it runs fine during light tasks. You suspect the power supply is failing. Which tool should you use to confirm the power supply's output voltages are within ATX specification?
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
✓
A multimeter
A multimeter is the correct tool for measuring DC voltages from a power supply. The ATX specification defines acceptable voltage ranges (e.g., +12V ±5%), and a multimeter can verify these under load. Other tools like a PSU tester or loopback plug may indicate basic function but don't measure actual voltage levels accurately.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A power supply tester
Why it's wrong here
A power supply tester provides a quick, basic check for the presence of voltage on the various rails (+12V, +5V, +3.3V) and verifies the Power Good signal status. However, these testers typically operate without applying significant load to the power supply. This means a power supply tester might report a "good" status even if the power supply is failing intermittently or delivering unstable voltages only when the system is under actual operational load, which is crucial for diagnosing random shutdowns.
- ✓
A multimeter
Why this is correct
A digital multimeter (DMM) is the most accurate and precise tool for diagnosing power supply issues like random shutdowns. It allows a technician to directly measure the DC voltage output on each power rail (+12V, +5V, +3.3V) at the motherboard's power connectors (e.g., 24-pin ATX, 8-pin EPS) while the computer is operating, ideally under load. This enables precise verification against ATX specification tolerances (typically +/- 5% for +12V and +5V, +/- 4% for +3.3V), revealing intermittent voltage drops or instability that a basic power supply tester would miss.
- ✗
A loopback plug
Why it's wrong here
A loopback plug is a diagnostic tool specifically designed to test the functionality and integrity of input/output ports by sending a signal out and immediately routing it back into the same port. For example, a USB loopback plug verifies the data lines of a USB port, and a network loopback plug tests a network interface card (NIC). This tool has no capability to measure electrical voltages, current, or diagnose power supply stability issues within a computer system.
- ✗
An ESD strap
Why it's wrong here
An Electrostatic Discharge (ESD) strap is a critical safety device worn by technicians to prevent static electricity buildup from damaging sensitive electronic components. It works by safely grounding the technician, equalizing electrical potential between the technician and the computer chassis, thus preventing sudden discharges. While essential for preventing damage during hardware installation or troubleshooting, an ESD strap is purely a protective measure and possesses no diagnostic capabilities for measuring voltage, current, or assessing power supply performance.
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Same concept, more angles
2 more ways this is tested on 220-1201
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 diagnosing a PC that will not power on. The multimeter shows 0V on all pins of the 24-pin connector when the PSU is plugged in and the power switch is on. What is the most likely cause?
hard- A.The motherboard is shorted, preventing the PSU from starting.
- B.The power supply is completely dead and needs replacement.
- ✓ C.The AC power cord is loose or the wall outlet is dead.
- D.The front panel power switch is faulty.
Why C: If no voltages are present, the PSU is not receiving AC power or its internal circuits are dead. The technician should check the AC outlet, power cord, and PSU switch first before concluding the PSU is faulty.
Variation 2. A desktop PC fails to power on. The technician measures the voltage on the 24-pin motherboard connector and finds that the purple wire (5VSB) reads 4.9V, but the green wire (PS_ON) reads 0V when the power button is pressed. What does this indicate?
hard- ✓ A.The power supply is faulty and needs replacement.
- B.The motherboard is not sending the PS_ON signal, likely due to a fault.
- C.The power supply's +12V rail is shorted, causing overcurrent protection.
- D.The front panel power switch is stuck in the closed position.
Why A: A desktop PC fails to power on. Measurements: 5VSB is present (4.9V is within tolerance), indicating the power supply is receiving AC power and its standby circuitry is working. When the power button is pressed, PS_ON is pulled low (0V) by the motherboard, which is the correct signal to request the PSU to turn on. Since the PSU does not start (fans don't spin, no other outputs), the fault lies within the power supply itself. A faulty PSU may have a failed main switching circuit or other internal defect preventing it from responding to the PS_ON signal. Therefore, the power supply should be replaced. Option B is incorrect because a low PS_ON indicates the motherboard is functioning correctly in this regard.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 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 220-1201 exam.