220-1201 Practice Question: A technician is troubleshooting a PC that shuts…

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 voltage regulator is failing.

  Why it's wrong here

  Motherboard voltage regulators (VRMs) are responsible for converting the +12V rail from the power supply into the much lower, precise voltages required by components like the CPU and RAM. If a VRM were failing, the issue would typically manifest as instability or incorrect voltage at the component itself, while the +12V output from the PSU would remain within specification. Since the measurement indicates the +12V rail is already low at the PSU output, the problem lies with the power supply's ability to generate or regulate that voltage, not with the motherboard's subsequent conversion.

• ✓

  The power supply is failing and needs replacement.

  Why this is correct

  The ATX specification dictates that the +12V rail must remain within a ±5% tolerance, meaning it should be between 11.4V and 12.6V. A measured reading of 11.2V falls below this acceptable range, indicating that the power supply is unable to maintain the required voltage stability. This undervoltage condition can lead to system instability, unexpected shutdowns, or component damage, making a power supply replacement necessary to restore proper operation and prevent further issues.

• ✗

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

  Why it's wrong here

  While an excessive current draw can indeed cause a voltage drop, a properly functioning power supply is designed with overcurrent protection (OCP) and overvoltage protection (OVP) mechanisms. Instead of allowing the +12V rail to sag significantly below its specified tolerance to 11.2V, a healthy PSU would typically activate its protection circuits, leading to a complete shutdown of the system or a current limit, rather than operating continuously with an out-of-spec voltage. The observed low voltage suggests a failure in the PSU's internal regulation, not merely an overloaded but otherwise healthy unit.

• ✗

  The AC input voltage is too low.

  Why it's wrong here

  If the AC input voltage supplied to the power supply were too low, it would generally affect all DC output rails proportionally, causing the +5V and +3.3V rails to also drop below their respective tolerances. Since the problem description implies that only the +12V rail is significantly out of specification while other rails are stable, the issue is isolated to the +12V rail's internal regulation or components within the power supply itself, rather than a problem with the incoming utility power.

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