A technician is troubleshooting a CAD workstation that powers on normally, boots into the … — CompTIA A+ (Core 1 & Core 2)

A technician is troubleshooting a CAD workstation that powers on normally, boots into the operating system, and passes basic diagnostic tests. However, whenever a 3D GPU-and-CPU rendering job is initiated, the system abruptly powers down without displaying a Blue Screen of Death (BSOD) or generating crash dump files. The technician connects a digital multimeter to an unpopulated 4-pin peripheral connector to measure the $+12\text{V DC}$ power output. At system idle, the multimeter measures $+12.1\text{V DC}$ . As soon as the rendering workload begins, the reading drops to $+11.2\text{V DC}$ right before the system shuts down. Which of the following best identifies the root cause of this failure?

The power supply unit is failing under load because the $+12\text{V DC}$ rail drops below the ATX standard minimum tolerance threshold of $+11.4\text{V DC}$ .Answer
B
The system memory modules are populated in non-matching motherboard slots, causing dual-channel bandwidth failure during heavy rendering.
C
The system is triggering a hardware safety shutdown because desktop SO-DIMM modules were installed instead of standard DIMM modules.
D
The CPU is experiencing a POST code initialization failure resulting from an uncalibrated motherboard thermal sensor readout.

Answer

The power supply unit is failing under load because the

+12\text{V DC}

rail drops below the ATX standard minimum tolerance threshold of

+11.4\text{V DC}

According to standard CompTIA troubleshooting guidelines and ATX power supply specifications, power supplies must maintain output voltages within a

\pm 5\%

tolerance window under all load conditions. For the

+12\text{V DC}

rail—which supplies main power to high-draw components like the CPU VRM and GPU—the acceptable operational limits are

+11.4\text{V DC}

+12.6\text{V DC}

. A measured drop to

+11.2\text{V DC}

under heavy rendering load represents a

-6.67\%

voltage drop, violating ATX specifications. This voltage sag causes system protection circuits to instantly shut down the machine to prevent hardware damage, resulting in sudden powering off without generating OS crash logs or BSOD screens.

Step-by-Step Solution

Identify ATX power supply voltage tolerance standards for the

+12\text{V DC}

rail.

ATX standards dictate a

\pm 5\%

allowable voltage fluctuation range.

Power supplies must maintain stable output voltages within specific bounds to prevent hardware instability or component damage.

Calculate the acceptable voltage range for a

+12\text{V}

output rail.

Minimum allowed voltage

= 12.0\text{V} \times 0.95 = 11.4\text{V DC}

; Maximum allowed voltage

= 12.0\text{V} \times 1.05 = 12.6\text{V DC}

This establishes the empirical baseline for evaluating multimeter diagnostic readings under load.

Compare the observed multimeter voltage reading against the minimum ATX tolerance threshold.

The observed voltage under load is

+11.2\text{V DC}

, which is less than the

+11.4\text{V DC}

minimum threshold.

A drop below

+11.4\text{V DC}

(

-6.67\%

) indicates that the PSU's voltage regulator circuit or capacitors cannot maintain regulation under transient load, causing low-voltage undervoltage protection shutdowns.

Key Concept

ATX Power Supply Voltage Tolerances and Dynamic Load Diagnostics

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