This chapter covers CompTIA A+ 220-1101 objective 5.1: Troubleshoot PC hardware issues. You will learn the systematic troubleshooting methodology, common PC hardware failures (power supply, motherboard, CPU, RAM, storage, cooling, and peripherals), and how to isolate and resolve each issue. Approximately 10-15% of the exam questions touch on troubleshooting scenarios, making this a high-yield area. Mastering these techniques is essential for both the exam and real-world IT support.
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Troubleshooting a PC that won't boot is like a doctor diagnosing a patient who collapsed. The doctor first checks vital signs (power supply output, POST beep codes) before ordering an MRI. If the patient has no pulse, you don't check for a broken toe—you address the life-threatening issue first. Similarly, if the PC has no power, you check the power cord, outlet, and PSU before suspecting a bad CPU. The doctor uses a stethoscope to listen for heart sounds; a technician uses a multimeter to measure voltage rails. If the patient is breathing but unresponsive, the doctor checks for a stroke; if the PC powers on but shows no display, you check the monitor cable and GPU seating. The doctor's differential diagnosis lists possible causes from most likely to least likely; the technician's troubleshooting theory (6-step CompTIA process) does the same: identify the problem, establish a theory of probable cause, test the theory, establish a plan of action, implement the solution, and verify full system functionality. Just as a doctor wouldn't prescribe antibiotics for a viral infection, a technician shouldn't replace a motherboard without first checking RAM and power connections. The mechanistic parallel is that both professionals follow a systematic, evidence-based process to isolate and correct the root cause, not treat symptoms.
Introduction to PC Hardware Troubleshooting
CompTIA A+ 220-1101 objective 5.1 requires you to apply the best practice methodology to resolve hardware problems. The official CompTIA A+ troubleshooting theory consists of six steps: 1. Identify the problem. 2. Establish a theory of probable cause (question the obvious). 3. Test the theory to determine the cause. 4. Establish a plan of action to resolve the problem and implement the solution. 5. Verify full system functionality and, if applicable, implement preventive measures. 6. Document findings, actions, and outcomes.
This methodology is not just for the exam—it is the standard in IT support. The exam tests your ability to apply these steps in scenario-based questions. You must know the order and what each step entails.
Power Supply Issues
The power supply unit (PSU) converts AC mains power to DC voltages (+3.3V, +5V, +12V, -12V, +5VSB). A failed PSU can cause no power, intermittent shutdowns, or component damage.
No power (system completely dead): Check the AC outlet, power cord, PSU switch (I/O), and PSU fan. Use a multimeter to test the green wire (PS_ON) on the 24-pin connector—when shorted to ground, the PSU should start. If the fan doesn't spin, the PSU is likely dead.
Intermittent shutdowns: Often due to overheating or a failing PSU under load. Measure the +12V rail under load—it should be within ±5% (11.4V to 12.6V). Voltage drops below 11.4V may cause random crashes.
No POST but fans spin: Insufficient power to the CPU or motherboard. Try a known-good PSU.
Trap: Candidates often replace the motherboard when a failing PSU causes no POST. Always test the PSU first.
Motherboard and POST Issues
The Power-On Self-Test (POST) is a diagnostic sequence the BIOS/UEFI runs to check hardware before loading the OS. POST failures are indicated by beep codes, LED codes, or blank screen.
- Beep codes: Vary by BIOS manufacturer (AMI, Award, Phoenix). One short beep usually means POST passed. Continuous long beeps indicate memory failure. No beeps at all may mean a dead CPU or motherboard. - Common POST failures: - No video: Check monitor cable, GPU seating, and power to GPU. If using integrated graphics, ensure the monitor is connected to the correct port. - RAM failure: Reseat RAM sticks, try one stick at a time in different slots. Use known-good RAM. - CPU failure: Check for bent pins on the CPU socket, ensure the CPU power connector (4/8-pin) is plugged in. Listen for beep codes. - Trap: A blank screen with fans spinning is often misdiagnosed as a dead GPU. It could be incompatible RAM, a loose CPU power cable, or a dead motherboard.
CPU and Cooling Issues
Overheating is the most common CPU issue. The CPU should idle at 30-50°C and under load up to 80-90°C (varies by model). Exceeding the Tjunction (thermal junction) temperature causes thermal throttling or shutdown.
Symptoms of overheating: Random shutdowns, slowdowns, high fan noise.
Causes: Dust-clogged heatsink, failed fan, dried-out thermal paste, inadequate case airflow.
Troubleshooting: Check BIOS/UEFI temperature readings. Use software like HWMonitor. Clean the heatsink and fan, reapply thermal paste, ensure the CPU cooler is properly seated.
Trap: Candidates replace the CPU when the real issue is a failed cooler. Always check temperatures first.
RAM Issues
RAM failures cause blue screens (BSODs), application crashes, and system instability. The exam tests your ability to identify RAM-related symptoms.
- Common BSOD error codes:
- MEMORY_MANAGEMENT (0x1A)
- PAGE_FAULT_IN_NONPAGED_AREA (0x50)
- IRQL_NOT_LESS_OR_EQUAL (0x0A) – often RAM or driver related.
- Testing: Use Windows Memory Diagnostic (mdsched.exe) or MemTest86. Run at least one full pass.
- Reseating: Remove and reinsert RAM sticks. Ensure they click into place. Try different slots.
- Mixing RAM: Using different speeds or voltages can cause instability. The system will run at the slowest speed, but mismatched timings may lead to random crashes.
- Trap: Candidates assume a BSOD with IRQL_NOT_LESS_OR_EQUAL is always a driver issue. RAM is a common cause. Test memory first.
Storage Drive Issues
Hard disk drives (HDDs) and solid-state drives (SSDs) can fail mechanically or electronically. Symptoms include clicking noises (HDD), unrecognized drive, boot failure, or slow performance.
Clicking HDD: Indicates a mechanical failure (head crash). Immediate backup and replacement required.
SSD failure: Often silent—sudden drive not detected. Check SATA/power connections. Try a different cable or port.
Boot failure: "Boot device not found" or "No bootable device". Check BIOS boot order, drive connections, and if the drive appears in BIOS.
SMART status: Self-Monitoring, Analysis, and Reporting Technology. In BIOS or via tools like CrystalDiskInfo. A failing drive may have reallocated sectors, pending sectors, or high temperature. Immediate backup.
Trap: Candidates replace the drive without checking cables or BIOS settings. Always verify connections and boot order first.
Peripheral and Input Device Issues
Common issues with keyboards, mice, monitors, and USB devices.
Keyboard/mouse not working: Check USB port, try different port, check for driver issues in Device Manager (yellow exclamation). For wireless, check batteries and receiver.
No display: Check monitor power, cable connection, input source selection. Try a different cable or monitor.
USB device not recognized: Try different USB port, update chipset drivers, check for power supply issues (USB ports may not provide enough power).
Trap: Candidates replace the device when the issue is a faulty cable or port. Always test with known-good components.
Using the CompTIA Troubleshooting Methodology in Practice
When given a scenario on the exam, follow these steps:
Identify the problem: Gather information from the user (what happened, when, error messages). Reproduce the issue.
Establish a theory of probable cause: Start with the most obvious and likely causes (e.g., "Is the power cord plugged in?"). Consider multiple causes.
Test the theory: Swap known-good components, check connections, run diagnostics. If the theory is confirmed, proceed. If not, establish a new theory.
Establish a plan of action and implement: Determine the fix (replace PSU, reseat RAM, etc.) and execute it safely.
Verify full system functionality: Ensure the original issue is resolved and no new issues were introduced. Test all related functions.
Document: Record the problem, solution, and any parts replaced for future reference.
Common Exam Traps
Trap 1: Jumping to conclusion without verifying. E.g., user says "My computer won't turn on" and you immediately replace the PSU without checking the power cord.
Trap 2: Ignoring the obvious. Always check cables, power switches, and simple things first.
Trap 3: Not testing the solution under load. A PSU may work at idle but fail under load.
Trap 4: Misinterpreting beep codes. Know the common patterns for major BIOS manufacturers.
Trap 5: Assuming a BSOD is always software. Hardware issues (RAM, HDD, PSU) are equally common.
Key Numbers and Values to Memorize
PSU voltage tolerances: ±5% for +3.3V, +5V, +12V. So +12V can range from 11.4V to 12.6V.
+5VSB (standby): always present when PSU is plugged in (even when off). ~2A capacity.
CPU idle temp: 30-50°C; load: up to 90°C (varies). Tjunction max often 100°C.
RAM voltage: DDR4 typically 1.2V; DDR3 1.5V.
POST beep codes: Award BIOS: 1 short = OK, 1 long + 2 short = video error. AMI BIOS: 1 short = OK, 2 short = parity error, 3 short = base 64K RAM failure.
Windows Memory Diagnostic: run from Administrative Tools or type mdsched.exe in Run.
SMART attributes: Reallocated Sector Count (raw value > 0 indicates bad sectors).
Advanced Troubleshooting Scenarios
Intermittent shutdowns under load: Could be PSU, overheating, or motherboard VRM failure. Monitor voltages and temperatures.
No POST after adding new hardware: Often due to insufficient PSU wattage or incompatible RAM. Remove new hardware and test.
System boots but no display: Check GPU seating, power connectors, monitor input. Try integrated graphics if available.
Blue screen after driver update: Boot into Safe Mode, roll back driver, or use System Restore.
By mastering these concepts and the troubleshooting methodology, you will be well-prepared for 220-1101 exam questions and real-world hardware troubleshooting.
Identify the Problem
Gather information from the user: What symptoms are you seeing? When did the problem start? Were there any recent changes (new hardware, software, driver updates)? Reproduce the issue to confirm. For a no-power scenario, ask if the power cord is plugged in, if the outlet works, and if any lights or fans come on. Document error messages, beep codes, or LED indicators. This step is critical because it sets the direction for the entire troubleshooting process. On the exam, the first step in any troubleshooting scenario is always to identify the problem, not to jump into replacing parts.
Establish a Theory of Probable Cause
Based on the symptoms, list likely causes starting with the most obvious. For a no-power issue, the theory might be: faulty power cord, dead outlet, failed PSU, or motherboard failure. Question the obvious—check the power cord and outlet before suspecting the PSU. Consider multiple causes; for intermittent shutdowns, the theory could include overheating, PSU overload, or failing capacitor. On the exam, you may be asked to select the most probable cause from a list. Always start with the simplest and most common cause.
Test the Theory to Determine Cause
Use diagnostic tools and component swapping to confirm or rule out the theory. For a suspected PSU failure, use a multimeter to measure voltage rails on the 24-pin connector (green wire to ground to start the PSU). Or swap with a known-good PSU. If the theory is that RAM is faulty, run Windows Memory Diagnostic or MemTest86. If the test confirms the theory, proceed to the next step. If not, revise the theory and test again. On the exam, you might need to choose the best tool or test to confirm a suspected cause.
Establish a Plan of Action and Implement
Once the cause is identified, determine the fix. For a failed PSU, the plan is to replace it with a compatible unit (same wattage or higher, correct connectors). For a bad RAM stick, replace it or reseat it. For overheating, clean the heatsink and fan, reapply thermal paste, or replace the cooler. Implement the solution safely—power off the system, use anti-static precautions, and follow manufacturer instructions. On the exam, you may be given a scenario and asked what the next step should be after identifying the cause.
Verify Full System Functionality
After implementing the fix, test the system to ensure the original problem is resolved and no new issues have been introduced. Boot the system, run stress tests (e.g., Prime95 for CPU, MemTest for RAM), and check for error messages. For a PSU replacement, verify that all voltages are within spec under load. Also test peripherals and any related functions. If the issue is resolved, proceed to documentation. If not, re-enter the troubleshooting loop. On the exam, you must remember that verification is a separate step after implementation.
Document Findings and Outcomes
Record the problem description, steps taken, root cause, solution implemented, and any parts replaced. Include error codes, beep patterns, and test results. Good documentation helps with future troubleshooting and tracking recurring issues. On the exam, you may be asked why documentation is important—the answer is to assist future troubleshooting and identify trends. This step is often overlooked but is a required part of the CompTIA methodology.
In a large enterprise IT environment, hardware troubleshooting often involves hundreds of desktops and laptops. One common scenario is a batch of identical desktops experiencing random shutdowns under load. A junior technician might replace the PSU on each machine, but a senior engineer would first check the system event logs for WHEA-Logger errors (indicating hardware issues) and measure internal temperatures. In one real case, the issue was traced to a BIOS bug that caused the CPU to overheat due to a faulty fan curve. The solution was a BIOS update, not hardware replacement. This saved the company thousands of dollars and avoided unnecessary downtime.
Another enterprise scenario involves SSD failures in a server farm. SMART monitoring tools (e.g., Dell OpenManage, HP iLO) report reallocated sector counts. The engineer must decide whether to replace the drive proactively or wait for failure. The standard practice is to replace any drive with a reallocated sector count above a threshold (e.g., 10) and to ensure backups are current. In a misconfigured environment, the monitoring alerts may be ignored, leading to catastrophic data loss. Proper documentation and automated alerts are critical.
A third scenario is a remote user whose laptop won't boot. The helpdesk technician walks the user through checking the power adapter (LED on the brick), reseating the battery, and trying a hard reset (remove battery and AC power, hold power button for 30 seconds). In many cases, the issue is a stuck power state. If the laptop still won't power on, the technician sends a replacement adapter before declaring the motherboard dead. This avoids unnecessary motherboard replacements and reduces return shipping costs. The key lesson: always start with the simplest, most common causes, especially in remote troubleshooting where component swapping is limited.
The 220-1101 exam tests objective 5.1 (Troubleshoot PC hardware issues) through scenario-based multiple-choice questions. You must apply the CompTIA troubleshooting methodology in order. The most common wrong answers involve skipping steps, especially jumping to a solution without identifying the problem or testing the theory. For example, a question might describe a user whose PC won't boot after a power outage. The wrong answer is "Replace the PSU" because the candidate assumes the PSU is dead. The correct answer is "Check the power cord and outlet" because the problem could be a tripped circuit breaker.
Another trap involves beep codes. The exam may provide a beep pattern (e.g., one long, two short) and ask what component is failing. Candidates who don't memorize common beep codes for Award and AMI BIOS will guess incorrectly. For Award BIOS, one long, two short indicates a video error. For AMI, continuous long beeps indicate memory failure.
A third trap is confusing symptoms of RAM failure with storage failure. Both can cause BSODs, but RAM errors often produce specific codes like MEMORY_MANAGEMENT or PAGE_FAULT_IN_NONPAGED_AREA, while storage failures produce INACCESSIBLE_BOOT_DEVICE or UNEXPECTED_STORE_EXCEPTION. The exam expects you to differentiate based on the error code.
Numbers to memorize: PSU voltage tolerances (±5%), typical CPU idle/load temperatures, and the order of the troubleshooting steps. The exam may ask "What is the first step in the troubleshooting process?" The answer is always "Identify the problem."
Edge cases: The exam loves to test scenarios where a hardware issue appears as a software problem. For example, a failing PSU can cause random crashes that look like a driver issue. The correct approach is to check the event log for hardware errors (WHEA-Logger) and test the PSU under load.
To eliminate wrong answers, focus on the underlying mechanism. If a question describes a symptom, ask yourself: "What component would cause this specific symptom?" For no POST with fans spinning, the cause is likely RAM, CPU, or motherboard—not the PSU (since fans spin). For a clicking noise from the drive, it's the HDD, not the SSD. By reasoning from mechanism, you can eliminate distractors.
The CompTIA troubleshooting methodology has 6 steps in order: Identify problem, Establish theory, Test theory, Plan/Implement, Verify, Document.
PSU voltage tolerances are ±5%: +12V must be between 11.4V and 12.6V.
Common POST beep codes: Award 1 long + 2 short = video error; AMI continuous long = memory failure.
RAM errors often produce BSOD codes MEMORY_MANAGEMENT (0x1A) and PAGE_FAULT_IN_NONPAGED_AREA (0x50).
Overheating CPU symptoms: random shutdowns, high fan noise, thermal throttling. Check temperatures in BIOS or with software.
A clicking sound from the drive indicates HDD mechanical failure—immediate backup required.
Always check the obvious first: power cord, outlet, power switch, cable connections.
Documentation is the final step and helps future troubleshooting.
Use a multimeter to test PSU voltage rails; use Windows Memory Diagnostic or MemTest86 for RAM.
SSDs can fail suddenly without warning; monitor SMART status and maintain backups.
These come up on the exam all the time. Here's how to tell them apart.
PSU Failure Symptoms
No power at all (fans don't spin, no lights)
Intermittent shutdowns under load
Burning smell or visible smoke from PSU
Voltage rails out of spec (e.g., +12V below 11.4V)
System works with a known-good PSU
Motherboard Failure Symptoms
Fans spin but no POST (no beeps, no display)
Random crashes or freezes not related to load
Bulging or leaking capacitors on motherboard
Diagnostic LEDs or beep codes indicate motherboard
System works with a known-good motherboard
Mistake
If the PC fans spin, the PSU is definitely good.
Correct
Fans can spin even if the PSU is failing under load. The PSU may provide enough power to spin fans but not enough to run the CPU or GPU. Always test voltages under load with a multimeter or a PSU tester.
Mistake
A blue screen always means a software or driver issue.
Correct
Blue screens are often caused by hardware failures, especially RAM, storage, and PSU. Error codes like MEMORY_MANAGEMENT (0x1A) indicate RAM issues, while WHEA_UNCORRECTABLE_ERROR (0x124) indicates hardware failure (CPU, cache, or motherboard). Always consider hardware first.
Mistake
If the computer doesn't beep during POST, the motherboard is dead.
Correct
Many modern motherboards have a small speaker or LED for POST codes, but some don't have a speaker at all. Also, a dead CPU or RAM can cause no beeps. Check for other indicators like diagnostic LEDs or a POST card before concluding the motherboard is dead.
Mistake
Reseating RAM always fixes memory problems.
Correct
Reseating can fix poor contact, but if the RAM stick is physically damaged or has failed, reseating won't help. Use a memory diagnostic tool to confirm. Also, reseating in the same slot may not work if the slot itself is faulty.
Mistake
SSDs never fail suddenly.
Correct
SSDs can fail suddenly due to controller failure, NAND wear, or power surges. Unlike HDDs, they often give no warning (no clicking sounds). Regular backups and SMART monitoring are essential.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
The first step is to identify the problem. This involves gathering information from the user, reproducing the issue, and noting any error messages or beep codes. You should always question the obvious before moving to more complex theories. On the exam, if a question asks 'What should you do first?', the answer is almost always to identify the problem by asking the user or checking the symptoms.
A continuous long beep typically indicates a memory (RAM) failure. On AMI BIOS, this is the standard pattern. On Award BIOS, continuous long beeps may also indicate a RAM problem. The solution is to reseat the RAM, try one stick at a time, or replace the faulty module. If using a beep code reference, always refer to the specific BIOS manufacturer's chart.
You can test a PSU using a multimeter. First, unplug the PSU from the motherboard. Use a paperclip to short the green wire (PS_ON) to any black wire (ground) on the 24-pin connector. This should start the PSU fan. Then measure voltages: red wires should be +5V, yellow +12V, orange +3.3V, purple +5VSB. Each should be within ±5% of the nominal value. Also check the gray wire (Power Good) for +5V. If any rail is out of spec, replace the PSU.
Random shutdowns under load (like gaming) are often caused by overheating (CPU or GPU) or a failing PSU that cannot deliver sufficient power. Check temperatures using software like HWMonitor. If temps are above 90°C, clean the heatsink and fan, reapply thermal paste, or improve case airflow. If temps are normal, test the PSU under load—monitor the +12V rail; if it drops below 11.4V, replace the PSU.
This error means the BIOS/UEFI cannot find a bootable operating system on any connected drive. Common causes: the boot order is incorrect (e.g., trying to boot from a USB drive that is not connected), the hard drive is disconnected or failed, or the MBR/GPT is corrupted. First, check BIOS boot order and SATA connections. If the drive is detected, run a startup repair or check for OS corruption. If the drive is not detected, it may be dead.
Symptoms of bad RAM include blue screens with memory-related error codes (e.g., MEMORY_MANAGEMENT), random crashes, and application errors. The best way to test is to run Windows Memory Diagnostic (type mdsched.exe in Run) or MemTest86. If errors are found, replace the faulty stick. Also try reseating the RAM and testing sticks one at a time to isolate the bad module.
First, check if the monitor is powered on and the cable is securely connected. Try a different cable or monitor. If using a dedicated GPU, ensure it is properly seated and has power connectors. Try connecting the monitor to the motherboard's video output (if the CPU has integrated graphics) to rule out a GPU failure. If still no display, listen for beep codes—a missing GPU may produce a video error beep pattern.
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