Troubleshooting Electrical and Power Issues

A Step-by-Step Guide

A practical, step-by-step framework for safely diagnosing and resolving common power-related problems in computer systems.
Author

Chuck Nelson

Published

October 18, 2025

1 Purpose

This document provides a practical, step-by-step framework for safely diagnosing and resolving common power-related problems in computer systems. This guide will equip you with a systematic approach to isolate the root cause of a power issue, from the wall outlet to the internal components.

2 What You’ll Learn

By the end of this reading, you will be able to:

  • Identify common symptoms of a failing power supply.
  • Follow a systematic troubleshooting flowchart to isolate a power problem.
  • Understand the safe way to use a multimeter to test PSU DC voltages.

This reading maps to the following program and course learning outcomes:

  • Program Learning Outcomes (PLOs):
    • 6. Maintain environment: This entire document is focused on the core maintenance and troubleshooting process for a critical system component.
  • Course Learning Outcomes (CLOs):
    • 3. Troubleshoot hardware and basic network components: This guide provides a direct, practical application of troubleshooting skills to power systems.

This exercise will help you develop the following skills and knowledge, which align with the O*NET SOC Code 15-1232.00 for Computer User Support Specialists.

Learning Objective O*NET KSAs Technologies Used
Follow a systematic process to isolate power issues. Knowledge: Computers & Electronics
Skills: Troubleshooting, Critical Thinking
Abilities: Problem Sensitivity		 Multimeter, PSU Tester
Safely test PSU voltages with a multimeter. Knowledge: Computers & Electronics
Skills: Troubleshooting, Equipment Selection		 Multimeter

3 A Systematic Approach to Troubleshooting

When a computer fails to power on or behaves erratically, it is often due to a power-related issue. A systematic approach is crucial to quickly and safely identify the source of the problem. Never assume the cause; always test in a logical sequence.

4 Safety is Non-Negotiable

Before you begin, you must understand the risks. AC power from the wall is dangerous. Never open the casing of a Power Supply Unit (PSU), as its internal capacitors can hold a lethal charge long after it has been unplugged. The troubleshooting steps below are for testing a PSU’s output, not repairing its internal components.

4.1 Common Symptoms of Power Issues

  • The computer does not power on at all (no fans, no lights).
  • The computer powers on for a moment and then immediately shuts off.
  • Random, unexpected shutdowns or reboots during operation.
  • A burning smell or visible smoke from the back of the computer.
  • Error messages related to voltage or power during boot (less common).

4.2 The Troubleshooting Flowchart

Follow this sequence to logically isolate the problem.

flowchart TD
    A{Start: PC Fails to Power On} --> B{Is the wall outlet known to be good?};
    B -- No --> C[Test outlet with a known good device, like a lamp.];
    B -- Yes --> D{Is it plugged into a surge protector or UPS?};
    D -- Yes --> E{Bypass it. Plug PC directly into the known good wall outlet.};
    E --> F{Does it power on?};
    F -- Yes --> G[Problem is the surge protector/UPS. Replace it.];
    F -- No --> H{Check physical connections.};
    D -- No --> H;
    H --> I[Is the power cord firmly seated in the wall and the PSU? Is the PSU switch ON?];
    I -- No --> J[Correct the connection and re-test.];
    I -- Yes --> K{Test the PSU itself.};
    K --> L[Use a PSU tester OR safely use a multimeter on the DC connectors.];
    L --> M{Are the DC voltages correct? #40;+12V, +5V, +3.3V#41;};
    M -- No --> N[PSU is faulty. Replace it.];
    M -- Yes --> O[The issue is likely another component #40;motherboard, CPU, etc.#41; causing a short.];

    style G fill:#D0E7FF,stroke:#333
    style N fill:#D0E7FF,stroke:#333

4.3 Using a Multimeter to Test a PSU

If you do not have a dedicated PSU tester, a multimeter can help you verify if the PSU is providing the correct DC voltages. This should be done with extreme care.

  1. Disconnect the PSU: Unplug the PSU from the wall and disconnect all of its connectors from the computer’s components.

  2. Start the PSU: To test a modern ATX PSU, you must “jump-start” it. Use a small piece of wire or a paperclip to connect the green wire (PS_ON) pin to any black wire (Ground) pin on the 24-pin motherboard connector. This tricks the PSU into thinking it’s been turned on by the motherboard.

  3. Plug In and Power On: With the jumper in place, plug the PSU back into the wall and turn on its power switch.

  4. Test Voltages: Set your multimeter to the DC Voltage setting (e.g., 20V). Connect the multimeter’s black probe to any black wire (Ground) on a connector. Then, use the red probe to carefully touch the metal contacts for the other pins.

    • Yellow Wires: Should be +12V
    • Red Wires: Should be +5V
    • Orange Wires: Should be +3.3V

A healthy PSU should show voltages within a +/- 5% tolerance. If any voltage is significantly off or absent, the PSU is faulty and should be replaced.

5 Reflect and Review

ImportantReflection: 3-2-1

Now that you have reviewed this document, take a moment to reflect on your learning. In your Microsoft Teams Student Notebook, create a new page for this topic and write down the following:

  • 3 symptoms of a failing power supply.
  • 2 safety precautions to take before troubleshooting power.
  • 1 question you still have about using a multimeter.

This reflection is for your instructor to review and helps solidify your understanding of the concepts.

TipCheck on Learning

Test your understanding with the following questions. These questions provide retrieval practice and reinforce key concepts covered in this reading. In your Microsoft Teams Student Notebook, answer the following:

  1. A user’s PC won’t turn on. What is the very first thing you should check, before even touching the computer itself?
  2. Why should you never open the case of a PSU?
  3. To test a PSU with a multimeter, which two pins on the 24-pin connector must be connected to get it to turn on?
  4. You are testing a PSU’s Molex connector. You place the black probe on a black wire and the red probe on the yellow wire. What voltage should you expect to see?
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