Core 1 Domain 5: Hardware and Network Troubleshooting (28%)¶

Overview¶

This is the heaviest Core 1 domain, at 28%. Every objective starts "Given a scenario, troubleshoot..." and lists common symptoms. The skill being tested is simple to state and hard to fake: read a symptom, name the most likely cause, and pick the right next step. This note is organized as symptom tables for that reason.

The objectives are:

• 5.1 Troubleshoot motherboards, RAM, CPUs, and power.
• 5.2 Troubleshoot drive and RAID issues.
• 5.3 Troubleshoot video, projector, and display issues.
• 5.4 Troubleshoot common mobile device issues.
• 5.5 Troubleshoot network issues.
• 5.6 Troubleshoot printer issues.

The Troubleshooting Methodology¶

In the V15 objectives, CompTIA prints the troubleshooting methodology as a "competency standard" and states that it is not a formal tested objective in 220-1201. Learn it anyway. It is the thinking every scenario question expects, it still appears in training material, and it is tested on Network+.

flowchart TB
    A["1. Identify the problem<br/>(ask the user, gather info, check recent changes, back up data)"] --> B["2. Establish a theory of probable cause<br/>(question the obvious, research knowledge base)"]
    B --> C{"3. Test the theory"}
    C -->|Confirmed| D["4. Establish a plan of action<br/>and implement the solution"]
    C -->|Not confirmed| B
    D --> E["5. Verify full system functionality<br/>and implement preventive measures"]
    E --> F["6. Document findings, actions,<br/>and outcomes"]

The six-step troubleshooting methodology from the A+ objectives document. If a theory fails, you form a new one, or escalate.

Practical rules that fall out of it:

• Back up data before making changes when the problem involves storage or the OS.
• Question the obvious. Is it plugged in? Is the monitor on the right input? Is Wi-Fi turned off?
• Change one thing at a time, so you know which change fixed it.
• Escalate when the fix is outside your authority or skill.

5.1 Motherboards, RAM, CPUs, and Power¶

RAM checks: reseat modules, test one stick at a time, try a different slot, run Windows Memory Diagnostic (mdsched.exe) or MemTest86.

5.2 Drives and RAID¶

Key point: a degraded RAID 5 array is running without protection. One more failure loses the array. Replace the failed drive quickly, and make sure backups are current before the rebuild, because rebuilds stress the remaining drives.

5.3 Video, Projector, and Display¶

5.4 Mobile Device Issues¶

5.5 Network Issues¶

A fast network isolation path¶

flowchart TB
    A["User reports no network"] --> B{"Link light on NIC<br/>and switch port?"}
    B -->|No| B1["Check cable, port, NIC.<br/>Try a known good cable"]
    B -->|Yes| C{"ipconfig shows a valid IP?"}
    C -->|169.254.x.x| C1["DHCP problem:<br/>check server, scope, VLAN"]
    C -->|Valid| D{"Ping default gateway?"}
    D -->|Fails| D1["Local network issue:<br/>VLAN, firewall, switch"]
    D -->|Works| E{"Ping 8.8.8.8 by IP?"}
    E -->|Fails| E1["Router, ISP, or<br/>upstream firewall"]
    E -->|Works| F{"Resolve a name<br/>(nslookup)?"}
    F -->|Fails| F1["DNS problem:<br/>check DNS servers, flush cache"]
    F -->|Works| G["Application or<br/>proxy issue"]

A bottom-up path for isolating a network fault, from physical link to DNS.

5.6 Printer Issues¶

Toner not fused (smears or rubs off) is also common in questions even though it is not in the list above: the fuser is failing.

Hardware Tools for Troubleshooting¶

Exam Tips and Traps¶

1. Wrong date and time after power off means the CMOS battery is dead.
2. Swollen capacitors or battery - replace, never repair.
3. Clicking or grinding HDD - back up first, then replace.
4. Drive not in File Explorer - check Disk Management for an uninitialized disk.
5. Array missing - do not initialize the drives.
6. Ghost images - drum or cleaning. Smearing - fuser. Garbled - driver.
7. Frozen print queue - restart the Print Spooler.
8. 169.254 address - DHCP. Ping by IP works but not by name - DNS.
9. Jitter and VoIP - QoS. Port flapping - cable or NIC.
10. Projector shuts off by itself - overheating, clean the filter.
11. Cursor drifting on a laptop trackpad - consider a swollen battery.
12. Always check the obvious first: power, cables, input source, radios on.

Related Notes¶

• 03 - Hardware - How each component works
• 02 - Networking - Addressing, DHCP, Wi-Fi background for 5.5
• 01 - Mobile Devices - Mobile parts and connectivity
• 08 - Software Troubleshooting - The Core 2 counterpart for OS and app issues