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Hardware Troubleshooting

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CompTIA A+ 220-1201 & 220-1202

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1 Introduction & Exam Overview

About the CompTIA A+ Certification Exam Domains & Study Strategy

2 Core 1 Domain 1: Mobile Devices (13%)

Laptop Hardware & Components Laptop Features & Display Types Mobile Device Connectivity & Accessories Mobile Operating System Features Mobile Device Synchronization & Data Transfer

3 Core 1 Domain 2: Networking (23%)

TCP/IP Fundamentals & the OSI Model Common Ports & Protocols Wireless Networking Standards Network Hardware & Devices Network Configuration & Internet Connections Network Types & Topologies

4 Core 1 Domain 3: Hardware (25%)

Cables & Connectors RAM Types & Storage Devices Motherboards, CPUs & Power Supplies Printers & Multifunction Devices Peripheral Devices & Expansion Cards Network Cable Tools & Testing

5 Core 1 Domain 4: Virtualization & Cloud Computing (11%)

Virtualization Concepts Cloud Computing Models & Services Client-Side Virtualization in Practice

6 Core 1 Domain 5: Hardware & Network Troubleshooting (28%)

CompTIA Troubleshooting Methodology Hardware Troubleshooting Network Troubleshooting Printer Troubleshooting Display & Mobile Device Troubleshooting

7 Core 2 Domain 1: Operating Systems (28%)

Windows Editions & Features Windows Administrative Tools & Utilities Windows Command Line & PowerShell macOS & Linux Basics Windows Networking & File Sharing Windows Installation & Upgrade Methods

8 Core 2 Domain 2: Security (28%)

Physical & Logical Security Measures Malware Types & Threat Mitigation Wireless & Network Security Encryption & Data Protection

9 Core 2 Domain 3: Software Troubleshooting (23%)

Windows OS Troubleshooting Mobile OS & Application Troubleshooting Browser & Application Troubleshooting

10 Core 2 Domain 4: Operational Procedures (21%)

Documentation & Change Management Backup & Recovery Methods Safety & Environmental Procedures Scripting & Remote Access Technologies Privacy, Licensing & Organizational Policies

Hardware Troubleshooting

Key Takeaways Explain This Topic AI

POST (Power-On Self-Test) beep codes are vendor-specific; modern boards report faults via motherboard debug LEDs or a 2-digit hex POST code display rather than beeps.

Random shutdowns under load point to overheating or an undersized power supply; check temperatures (CPU under ~85-95C limits) and recalculate wattage before swapping parts.

RAM faults cause BSODs, lockups, and POST failure — test with Windows Memory Diagnostic (mdsched.exe) or MemTest86, swapping to one module at a time to isolate.

A clicking/grinding HDD is failing mechanically: back up immediately, then replace. Never run defrag on an SSD — rely on TRIM, which is on by default.

Never open a power supply unit; its capacitors store lethal charge even unplugged. Replace a failed PSU as a sealed unit and size it for the system TDP.

Last updated: October 2026

POST (Power-On Self-Test) and No-Boot Issues

At power-on, firmware (BIOS/UEFI) runs POST to verify the CPU, RAM, and basic devices before handing off to the bootloader. A failure stops the boot and is signaled by beep codes , motherboard debug LEDs (commonly a 4-light row labeled CPU/DRAM/VGA/BOOT), or a 2-digit hexadecimal POST code on enthusiast boards.

Representative Beep Codes (vary by AMI / Phoenix / Award)

  • Beeps Typical Meaning
  • 1 short Successful POST — normal boot
  • Continuous short Power or motherboard fault
  • 1 long, 2 short Video adapter failure
  • 1 long, 3 short Video / memory failure
  • 3 long Keyboard controller error
  • Continuous long RAM not detected or failed
  • No beep / no display CPU, motherboard, or PSU failure

Beep codes are not standardized — always confirm against the board manual. On modern UEFI systems, the DRAM or VGA debug LED staying lit tells you exactly which subsystem stalled.

Minimum-Hardware Isolation (No POST)

Confirm the outlet, the PSU rocker switch (rear), and a known-good power cable.

Look for the standby power LED on the motherboard — proves the PSU delivers 5VSB.

Verify the front-panel power button header is connected.

Strip to minimum hardware : CPU, one RAM stick, integrated graphics, no drives.

Reseat CPU, RAM, and GPU; clear CMOS (jumper or remove the CR2032).

Swap in a known-good PSU to rule out a dead supply.

Motherboard, CPU & Power Symptom Matrix

  • Symptom Likely Cause Action
  • Dead, no fans PSU or motherboard failure Test PSU/tester; inspect for swollen capacitors
  • Powers on, no display GPU/RAM/CPU fault Reseat, test GPU in another PC, check DRAM LED
  • Random shutdown under load Overheating or undersized PSU Check temps; recalc wattage
  • Clock/date resets Dead CMOS battery Replace CR2032
  • Boot loop Bad RAM, corrupt firmware, failed update Reseat RAM, clear CMOS, Safe Mode
  • Burning smell Shorted/overloaded component Power off immediately; isolate
  • Distended capacitor Aged/defective caps Replace motherboard
  • Intermittent BSOD Marginal RAM or failing drive Memory test; check SMART
  • CPU Overheating

Throttling, instability, or a shutdown seconds after boot signals a thermal problem. Fix order: blow dust from the heatsink/fans with compressed air; confirm the CPU fan spins and its header reads RPM in firmware; remove the cooler, clean old paste with 90%+ isopropyl alcohol , and apply a fresh pea-sized dot; verify all mounting points are seated; improve case airflow; and confirm the cooler is rated for the CPU's TDP . Most desktop CPUs throttle around 95-100C and shut down at their thermal limit, so temperatures under sustained load should sit well below that.

RAM Troubleshooting

  • Symptom Cause Action
  • Won't POST Unseated/incompatible RAM Reseat; check QVL
  • Recurring BSODs Failing module Test one stick at a time
  • Random app crashes Marginal RAM Run MemTest86 extended pass
  • Less RAM reported than installed Bad slot or stick Move sticks; test individually

Tools: Windows Memory Diagnostic ( mdsched.exe , reboots and scans) and MemTest86 (bootable USB, multiple thorough passes — let it run several cycles to catch intermittent faults).

Storage Troubleshooting

  • Symptom Cause Action
  • Drive missing in firmware Loose cable / wrong SATA mode Reseat; check AHCI vs RAID
  • Clicking / grinding (HDD) Mechanical failure Back up NOW; replace
  • Boot device not found Corrupt boot sector / dead drive Repair boot, check cable
  • SMART warning Imminent failure Back up; replace
  • SSD slowing / nearing TBW Write endurance exhausted Check SMART/TBW; plan swap

Never defragment an SSD. It has no heads, so fragmentation does not slow reads; defrag only burns finite write cycles. Rely on TRIM , enabled by default on modern Windows/macOS/Linux.

Power Supply & Safety

Random reboots under load, fans that twitch then die (over-current protection tripping), or a burning smell all implicate the PSU . Test with a PSU tester or a multimeter on the 24-pin (3.3V/5V/12V rails). Never open a PSU — its primary capacitors can hold a lethal charge even when unplugged . Replace it as a sealed unit and size it to the build's total wattage plus headroom.

A subtle PSU symptom is a system that powers on fine at idle but reboots only when the GPU spins up under a game or render — the supply cannot deliver peak 12V current to the graphics card. Recalculate the build's draw (CPU TDP plus GPU board power plus drives and fans) and add roughly 20-30% headroom; a supply running near 100% load runs hot and ages quickly. Loose or partially seated PCIe and EPS (CPU) power connectors produce the same intermittent reboots, so reseat every modular cable on both ends before condemning the unit.

Interpreting Symptoms vs. Components

Domain 5 questions reward pattern recognition — matching a described symptom to the single most likely failed part. Keep these high-value associations sharp:

Clock/date keeps resetting and BIOS settings are lost → dead CMOS battery (CR2032) , not the motherboard.

Distended (swollen) capacitors near the CPU socket → degraded board; replace the motherboard.

Burning smell or visible scorch → power off immediately, unplug, and isolate the shorted component; do not keep powering on.

Grinding or clicking from a spinning drive → mechanical HDD failure; back up before it dies.

Sluggish performance plus occasional BSODs → run a SMART check and a memory test; either a marginal drive or marginal RAM can produce both.

System indicators : a steady standby LED with no fans means the PSU has power but the board isn't starting; no LED at all means no standby voltage reaches the board.

A Worked Isolation Example

A workstation powers on (fans spin) but shows no display and gives no beep. Apply minimum-hardware isolation: remove the discrete GPU and connect the monitor to the integrated graphics output. If video returns, the discrete card is the fault — reseat it, test it in another machine, or replace it. If there is still no display, remove all but one RAM stick and move it to the first recommended slot; watch the DRAM debug LED . If the LED clears and the system POSTs, the original stick or slot was bad.

Methodically changing one variable at a time — exactly Step 3 of the methodology applied to hardware — isolates the failed part without guesswork or unnecessary parts replacement.