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Difficulty: HardMotherboard, RAM, CPU, and Power Issues

An IT technician is servicing a system after replacing the CPU cooler and modular power supply. When the power button is pressed, the power supply unit (PSU) makes a distinct clicking sound, the cooling fans turn for a fraction of a second, and the computer instantly powers down. Pressing the power button again has no effect until the AC power cable is unplugged and reattached. The technician confirms that total system power requirements are well within the PSU's rated continuous output. Which of the following is the most likely cause of this symptom?

  1. A short circuit or incorrectly plugged 12V EPS connector on the motherboard triggering the power supply's latching shutdown protection circuitAnswer
  2. B
    Corrupted BIOS firmware causing a failure during the initial Power-On Self-Test (POST) diagnostic check
  3. C
    System RAM installed in alternating DIMM slots causing a dual-channel memory configuration mismatch
  4. D
    The continuous power draw of the system hardware under heavy processing load exceeding the wattage capacity of the PSU

Answer

A short circuit or incorrectly plugged 12V EPS connector on the motherboard triggering the power supply's latching shutdown protection circuit
When a direct electrical short circuit occurs on a motherboard—such as a misplaced standoff shorting a trace or a reversed/pinched 12V auxiliary power cable—the power supply's Short Circuit Protection (SCP) or Over Current Protection (OCP) circuit trips instantaneously. This causes a click sound and cuts power in under a second. The PSU enters a latching state that requires complete removal of AC power to reset.

Step-by-Step Solution

1
Analyze the observed hardware symptom
The system shuts down in less than one second with an audible PSU click, and subsequent power button presses fail until AC power is cycled.
This behavior indicates a latching safety mechanism within the power supply unit.
2
Evaluate PSU protection features
Latching protection (OCP/SCP) trips immediately when a low-impedance short circuit is detected on any DC power rail (e.g., +12V, +5V, +3.3V).
To protect internal components from electrical fires or severe silicon damage, the PSU shuts down and refuses to restart until residual flea power clears upon AC line disconnection.
3
Differentiate from software, POST, and load-based failures
BIOS/POST errors allow fan spin to continue; memory configuration issues cause POST halts rather than latching PSU trips; under-wattage issues manifest under load.
Direct electrical short circuits are unique in causing sub-second latching power cuts.

Key Concept

Power supply unit short-circuit and over-current protection (SCP/OCP) latching behavior
Estimated Time:2m 0s
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Topics

Motherboard, RAM, CPU, and Power Issues

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