220-1201 Power Supply — Timed 10 Questions

Question 1

A technician is troubleshooting a PC that emits a high-pitched whining noise under load. The noise is coming from the power supply area. The system is stable and temperatures are normal. What is the most likely cause?

Accepted Answer

The PSU is experiencing coil whine due to electrical resonance.. Coil whine is a common phenomenon in power supplies and other components when electrical current passes through inductors, causing them to vibrate at audible frequencies. It is typically harmless and does not indicate a defect, though it can be annoying. If the system is stable, no replacement is needed.

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The PSU fan bearing is failing.

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The PSU is overheating and the thermal protection is activating.

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The PSU has a loose internal component rattling.

Question 2

A technician is selecting a power supply for a workstation that will run 24/7 in a dusty environment. The PSU will be installed in a case with limited airflow. Which PSU feature is most important to prioritize for long-term reliability in this scenario?

Accepted Answer

A fan with a fluid dynamic bearing and a dust filter.. In dusty environments with limited airflow, a PSU with a high-quality, sealed bearing fan (e.g., fluid dynamic bearing) and a dust-resistant design (e.g., honeycomb grill, dust filters) is critical. Additionally, a higher efficiency rating (e.g., 80 Plus Gold or better) reduces heat output, easing thermal stress. The most important single feature is the fan's reliability and the PSU's ability to handle particulate ingress.

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A high total wattage rating to ensure headroom.

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A modular cable design for easier cable management.

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An 80 Plus Bronze efficiency rating.

Question 3

A technician is replacing a power supply in an office desktop. The new PSU has a 24-pin main connector, but the motherboard has a 20-pin socket. What should the technician do?

Accepted Answer

Separate the detachable 4-pin section from the 24-pin connector and use the remaining 20-pin part.. Modern ATX power supplies often have a 24-pin connector that is backward compatible with 20-pin motherboards; the extra 4 pins can be slid or snapped off. This allows the PSU to work without modification. Forcing the 24-pin into a 20-pin socket could damage the board.

Answer

Use a 24-pin to 20-pin adapter.

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Force the 24-pin connector into the 20-pin socket.

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Return the PSU and buy one with a 20-pin connector.

Question 4

A technician is troubleshooting a PC that shuts down randomly after a few minutes of use. The technician measures the +12V rail with a multimeter and gets 11.2V. The +5V rail reads 4.9V, and the +3.3V rail reads 3.2V. What is the most likely diagnosis?

Accepted Answer

The power supply is failing and needs replacement.. The +12V rail is significantly below the ATX specification of ±5% (11.4V minimum), indicating a failing power supply. The other rails are within tolerance but the +12V is critical for CPU and GPU power. A failing PSU can cause random shutdowns as voltage drops under load. Replacement is necessary.

Answer

The motherboard voltage regulator is failing.

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The system is drawing too much current, causing voltage drop.

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The AC input voltage is too low.

Question 5

A technician is upgrading a server's power supply to support additional drives. The current PSU is a 750W unit with a single +12V rail rated at 62A. The new drives will add 5A to the +12V load. The total calculated +12V load is 58A. Is the current PSU adequate?

Accepted Answer

Yes, because 58A is less than 62A, so it is within specifications.. The PSU's +12V rail is rated for 62A, and the total load after adding drives is 58A, which is within the rating. However, it is good practice to leave headroom (typically 10-20%) to avoid running the PSU at maximum capacity, which can reduce efficiency and lifespan. In this case, the PSU is technically adequate but marginal.

Answer

No, because the PSU should not be loaded above 80% of its rating.

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No, because the total wattage of 750W is insufficient for the new drives.

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Yes, but only if the PSU is 80 Plus Gold certified or higher.

Question 6

A small business has several PCs that intermittently reboot or fail to start. The building's electrical system is old, and the technician suspects power quality issues. Which device should the technician recommend installing to protect the computers?

Accepted Answer

An uninterruptible power supply (UPS).. An uninterruptible power supply (UPS) provides battery backup and voltage regulation, protecting against surges, sags, and brownouts that can cause reboots or failures. A surge protector only guards against spikes, not low-voltage conditions. A UPS is the appropriate solution for unstable power.

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A power strip with a surge protector.

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A line conditioner (voltage regulator).

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A dedicated circuit from the breaker panel.

Question 7

A technician is building a new workstation for video editing and needs to ensure the power supply can handle dual GPUs and multiple hard drives. Which specification is most critical to check when selecting a PSU?

Accepted Answer

The combined amperage on the +12V rail(s).. The +12V rail provides power to the CPU, GPUs, and drives; its combined amperage determines how much power can be delivered to these components. For high-power builds, a single +12V rail with high amperage or multiple rails with sufficient combined capacity is essential. Neglecting this can lead to instability or shutdowns under load.

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The total wattage rating of the power supply.

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The number of SATA power connectors.

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The physical form factor (ATX, SFX, etc.).

Question 8

A technician is installing a new power supply in a high-end gaming PC. The PSU has two +12V rails rated at 20A each. The GPU requires a single +12V rail with at least 30A. What potential issue could arise?

Accepted Answer

The GPU may cause overcurrent protection to trip on one rail, causing shutdowns.. Multi-rail PSUs split the +12V output across separate rails, each with its own overcurrent protection. If the GPU draws more than 20A from one rail, it can trip the protection, causing shutdowns. Using a single-rail PSU or ensuring the GPU is connected across both rails (if the PSU allows) would avoid this.

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The PSU will automatically combine the rails to provide 40A to the GPU.

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The PSU will deliver stable power as long as the total wattage is sufficient.

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The GPU will automatically draw power from both rails equally.

Question 9

A user reports that their computer does not power on at all. The technician verifies the power cord is connected and the wall outlet works. When the PSU is turned on, no fans spin and no LEDs light up. What should the technician check first?

Accepted Answer

Check if the power supply's on/off switch is set to the '1' (on) position.. The power supply switch is a simple but common oversight; if it is in the off (0) position, no power reaches the system. Always verify this before more complex troubleshooting. Other steps like testing the PSU with a multimeter or paperclip test come after confirming the switch is on.

Answer

Replace the CMOS battery.

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Reseat the RAM modules.

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Test the PSU with a multimeter.

Question 10

A customer reports that their desktop PC randomly shuts down when playing a graphically intensive game. The system has a 500W power supply, a high-end GPU, and a CPU with a 125W TDP. What is the most likely cause of the shutdowns?

Accepted Answer

The power supply is undersized for the system's peak power demands.. The random shutdowns under load suggest the power supply cannot deliver enough wattage to sustain peak power draw from the GPU and CPU. A 500W PSU may be insufficient for a high-end gaming system, causing voltage drops or thermal overload protection to trigger. Upgrading to a higher-wattage PSU with adequate +12V rail capacity would resolve the issue.

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The GPU is overheating due to poor case airflow.

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The motherboard's VRM is failing due to age.

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The RAM is faulty causing memory errors during gaming.