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220-1201 Practice Question: A technician is diagnosing a PC that will not…
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?
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 AC power cord is loose or the wall outlet is dead.
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.
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 shorted, preventing the PSU from starting.
Why it's wrong here
A shorted motherboard would typically cause the Power Supply Unit (PSU) to activate its internal overcurrent or short-circuit protection, leading to an immediate shutdown of the main power rails (e.g., +12V, +5V, +3.3V) after attempting to start. However, the +5VSB (standby voltage) line is designed to remain active as long as the PSU receives AC power, providing continuous power for features like Wake-on-LAN. Therefore, if the motherboard were shorted, the technician would still likely measure +5VSB, not 0V on all pins.
- ✗
The power supply is completely dead and needs replacement.
Why it's wrong here
While a completely dead power supply unit (PSU) would indeed result in no voltage output, diagnosing it as 'dead' prematurely bypasses crucial initial troubleshooting steps. Before concluding a PSU failure, a technician must first verify that the unit is receiving adequate AC power from the wall outlet and through the power cord. If there is no AC input, the PSU cannot operate regardless of its internal condition, making external power verification the primary diagnostic step.
- ✓
The AC power cord is loose or the wall outlet is dead.
Why this is correct
If a multimeter reads 0V on all pins of the PSU's ATX connector, including the critical +5VSB (standby voltage) line, it indicates a complete absence of power reaching the power supply unit. The +5VSB line is always active when the PSU is plugged into a live AC source, even if the PC is 'off.' Therefore, no voltage at all strongly points to an issue with the external AC power delivery, such as a disconnected or faulty power cord, a tripped circuit breaker, or a dead wall outlet, making these the immediate points of investigation.
- ✗
The front panel power switch is faulty.
Why it's wrong here
A faulty front panel power switch would prevent the Power Supply Unit (PSU) from receiving the 'Power On' signal from the motherboard, thus preventing the main +12V, +5V, and +3.3V rails from activating. However, the +5VSB (standby voltage) line is independent of the power switch and remains active as long as the PSU is connected to a live AC source. If the switch were the sole issue, the technician would still measure +5VSB, contradicting the symptom of 0V on all pins.
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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.