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Difficulty: MediumMotherboard, RAM, CPU, and Power Issues

A technician is troubleshooting a desktop computer that experiences spontaneous shutdowns whenever resource-intensive tasks are performed. The system boots normally and operates fine during light idle usage. Using a multimeter to test the Power Supply Unit (PSU) output while the system is under heavy load, the technician measures +10.7 V on the +12 V power rail. Which of the following is the most likely cause of the system instability?

  1. The power supply unit is failing under load and dropping below acceptable ATX voltage tolerances.Answer
  2. B
    The RAM modules are installed in non-matching slots, preventing dual-channel memory voltage regulation.
  3. C
    The motherboard system firmware is misinterpreting POST diagnostic codes during heavy processing.
  4. D
    The system was incorrectly upgraded using an SO-DIMM module instead of standard desktop DIMMs.

Answer

The power supply unit is failing under load and dropping below acceptable ATX voltage tolerances.
According to standard ATX power supply specifications, the output voltage on the +12 V rail must remain within a ±5% tolerance band (+11.4 V to +12.6 V). A reading of +10.7 V is below the minimum threshold, indicating that the power supply cannot handle the current draw required during high-load operations, resulting in immediate thermal/power protection shutdowns.

Step-by-Step Solution

1
Analyze the observed system symptom and multimeter measurement.
The +12 V rail measured +10.7 V while the desktop system was under load.
Determining whether a power supply rail is operating within standard specification requires evaluating voltage tolerance.
2
Calculate the acceptable ATX voltage range for a +12 V DC power rail.
Standard ATX specifications require a ±5% tolerance range, meaning the voltage must stay between +11.4 V and +12.6 V.
System components rely on stable voltage within this window to maintain operational stability.
3
Compare the measured value (+10.7 V) against the minimum allowable threshold (+11.4 V).
+10.7 V is lower than +11.4 V, representing an unacceptable drop under load.
When a PSU cannot maintain adequate voltage under load, components like the CPU or GPU experience voltage starvation, leading to unexpected shutdowns.

Key Concept

ATX Power Supply Unit (PSU) Voltage Tolerances and Multimeter Troubleshooting
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Topics

Motherboard, RAM, CPU, and Power Issues

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