Chapter 5

Hardware and Network Troubleshooting

CompTIA A+ Core 1 (220-1201) Study GuideBased on the CompTIA A+ 220-1201 exam objectives

The biggest domain on the 220-1201 exam — 28% of your questions. This is also the domain where real-world experience matters most, because CompTIA doesn't just test whether you know what a part does. It tests whether you think like a technician.

It's 9:15 on a Tuesday morning. Your phone rings. "Hi, my computer won't turn on," the caller says. "It was working fine yesterday."

What do you ask first?

If your instinct is to say "Is it plugged in?" — congratulations, you're already troubleshooting. But there's a difference between randomly poking at symptoms and following a disciplined methodology that gets you to the answer fast, every time. That difference is what this chapter is about — and it's what CompTIA spends more than a quarter of the Core 1 exam testing.

> EXAM TIP: Troubleshooting questions are the single largest category on the 220-1201. CompTIA loves scenario-based questions here: "A user reports X. Which should the technician do FIRST?" or "Which is the MOST LIKELY cause?" The wrong answers are always plausible — they test whether you follow the methodology instead of jumping to conclusions.

5.1 The CompTIA 6-Step Troubleshooting Methodology

Before touching a single cable, memorize this sequence. CompTIA expects you to apply it, not just recite it:

1. Identify the problem — Gather information, question the user, identify symptoms, determine if anything changed, duplicate the problem if possible.
2. Establish a theory of probable cause — Question the obvious, consider multiple hypotheses.
3. Test the theory — Determine next steps to resolve the problem; if the theory is confirmed, determine the next steps. If not, re-establish a new theory.
4. Establish a plan of action — Identify potential effects of the fix before implementing it.
5. Implement the solution or escalate — Apply the fix or hand off with documentation.
6. Verify full system functionality and implement preventive measures — Then document findings, actions, and outcomes.

Why the order matters

Each step exists to prevent a specific, expensive mistake:

• Skipping Step 1 (identify) means you fix the wrong thing. The user says "the internet is down" but the actual problem is that their monitor cable came loose and they can't see anything. Ask questions first.
• Skipping Step 2 (theory) means shotgun troubleshooting — replacing parts at random until something works. Expensive and slow.
• Skipping Step 4 (plan of action) means you cause new damage. Rebooting a server to fix a print spooler without warning users? That's a career-limiting move. Always consider the blast radius of your fix.
• Skipping Step 6 (document) means the next technician — possibly you, three months later — starts from zero.

> EXAM TIP: When CompTIA asks "What should the technician do FIRST?" or "What is the NEXT step?", map the scenario to the six steps. If the technician just arrived and the user described symptoms, the answer is almost always something from Step 1 (gather more information, question the user, duplicate the problem). If they've already tested and confirmed a cause, the answer moves to Step 4 (plan of action considering effects). The exam constantly tests whether you know which step you're on.

A methodology walkthrough

Let's revisit that Tuesday morning call — "my computer won't turn on" — and run it through the methodology properly:

Step 1 — Identify. You ask: "When you press the power button, do any lights come on? Do you hear any fans?" The user says: "Nothing. Completely dead. No lights, no sounds." You also ask the golden question: "Did anything change? Any storms, any new devices, did anyone move the PC?" The user mentions a thunderstorm last night. Now you have real data, not just "won't turn on."

Step 2 — Theory. Dead PC + thunderstorm = probable power event. Theories, ranked: (a) tripped surge protector or dead outlet, (b) blown PSU, (c) fried motherboard. You question the obvious first — always check the simple, external things before assuming internal damage.

Step 3 — Test. You ask the user to check whether the surge protector's switch is on and whether other devices on the same outlet work. The lamp plugged into the same strip works. Theory (a) is eliminated. Next test: the PSU paperclip test, or swapping in a known-good PSU.

Step 4 — Plan. Before opening the case: "I'll need to power it down fully, unplug it, and ground myself. This won't affect your data — we're only testing the power supply."

Step 5 — Implement. The paperclip test shows the PSU fan doesn't spin. You replace the PSU. The PC boots.

Step 6 — Verify and document. You don't just confirm it powers on — you check that it boots to the OS, that all drives are detected, that the network works. Then you document: "PSU failed after reported power surge. Replaced with 650W unit. Recommended UPS. User advised on surge protection." You also implement the preventive measure: sell them a UPS, not just another surge strip.

> EXAM TIP: CompTIA loves asking about the LAST step. "After resolving the issue, what should the technician do next?" The answer is almost always verify full functionality and document. "Verify" alone is incomplete — the methodology specifically says verify AND document AND implement preventive measures. If "document findings" is an option, it's usually the expected answer for post-resolution questions.

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5.2 Power Issues: The Dead PC

Scenario: A small business owner calls. "My workstation is completely dead. Pressing the power button does nothing — no lights, no beeps, no fans. It worked Friday."

Walk through it:

No signs of life at all points to the power chain: wall outlet → power cable → PSU → motherboard. Work from the wall inward — always outside-in.

1. Verify the outlet. Plug a known-working device (phone charger, lamp) into the same outlet. If it's dead, check the breaker. This takes ten seconds and eliminates an entire category.
2. Check the power cable and PSU switch. The rocker switch on the back of the PSU (the "I/O" switch) gets bumped to "O" more often than anyone admits — especially after cleaning. Also try a different power cable; they're a common failure point and cost nothing to test.
3. Listen and look. When you press power: any fan twitch? Any LED blink? A fan that spins for half a second then stops suggests the PSU's overcurrent protection tripping — possibly a short on the motherboard or a failed component dragging a rail down.
4. The PSU paperclip test. Unplug the 24-pin ATX connector, bridge the green wire (PS_ON) to any black wire (ground) with a paperclip. If the PSU fan spins, the PSU can start — but this doesn't prove it delivers stable voltages under load. A PSU can pass the paperclip test and still be faulty.
5. Swap with a known-good PSU. This is the definitive test. If the system boots with a different PSU, you've found your culprit.

> EXAM TIP: For "no power" questions, CompTIA expects you to check external power first (outlet, cable, PSU switch) before internal components. An answer like "replace the motherboard" for a dead PC is almost always wrong — the motherboard is the LAST thing you suspect, not the first. Also know the PSU voltage rails: the 24-pin ATX connector delivers +3.3V, +5V, +12V, -12V, +5VSB (standby), and PS_ON.

Intermittent shutdowns are a different beast. A PC that randomly powers off — especially under load — usually means:

• Overheating (thermal shutdown — covered in 5.3)
• Failing PSU that can't sustain load (voltages droop when the GPU spins up)
• Loose power connectors (the 4/8-pin CPU power connector working its way loose from thermal cycling)

The burning smell. If a user reports a burning or ozone smell from the PC, power it off immediately and do not power it back on. This is usually a failed capacitor or a shorted component. Inspect visually — bulging or leaking capacitors on the motherboard are the classic sign. This is one of the few situations where you skip straight past the methodology's gentle steps: safety first.

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5.3 Overheating: The Silent Killer

Scenario: "My computer was fine, but now it shuts off whenever I play games or render video. It stays on if I'm just browsing."

This is a textbook thermal shutdown. Modern CPUs and GPUs protect themselves: when temperatures cross a threshold (typically 95–105°C for CPUs), the system force-powers-off to prevent silicon damage. The pattern — fine at idle, dead under load — is the giveaway.

Diagnosing heat:

1. Check the obvious first. Is the PC shoved into a cabinet with no airflow? Are the intake vents clogged with dust? I've seen "mysterious shutdown" cases solved by pulling the tower out from under a desk where it was suffocating. Question the obvious.
2. Listen to the fans. A fan that should be screaming under load but is silent has failed. A fan making grinding or clicking noises has a dying bearing — replace it before it seizes entirely.
3. Read the temperatures. Boot into BIOS/UEFI (which shows CPU temp) or use OS monitoring software. Idle temps should be 30–50°C; under load, 70–85°C is normal. Sustained 95°C+ means the cooling system is failing.
4. Inspect thermal paste. If the heatsink was recently removed — or if the system is 3+ years old — the thermal paste may be dried out or improperly applied. Too much paste insulates; too little leaves air gaps. A pea-sized dot in the center is the standard application.
5. Check airflow direction. Front/bottom fans should intake cool air; rear/top fans should exhaust hot air. A case with all fans blowing inward creates positive pressure but traps heat. Cable management matters too — a bird's nest of cables blocks airflow.

> EXAM TIP: CompTIA tests thermal concepts in scenario form: "A workstation shuts down during graphically intensive applications but operates normally otherwise. What is the MOST LIKELY cause?" The answer is overheating — specifically, check the GPU/CPU cooling. Distractor answers will mention the PSU or RAM. The "only under load" pattern is your signal for heat (or a PSU that can't sustain load — but heat is more common and the exam prefers it when temperatures are mentioned or implied).

Laptops overheat differently. They have tiny heatsinks and a single fan (sometimes two). Common laptop-specific causes:

• Blocked vents — using the laptop on a bed or couch smothers the intake vents on the bottom. This alone causes most laptop overheating.
• Dust-clogged heatsink fins — compressed air through the exhaust vent (with the fan held still so it doesn't overspin) clears this.
• Failed fan — if the fan never spins up, the laptop will thermal-throttle (slow to a crawl) before it shuts down. Throttling shows up as sudden, severe slowness under load — a useful diagnostic clue.
• Dried thermal paste — same as desktops, but harder to service.

Thermal throttling vs. thermal shutdown. Know the difference: throttling is the CPU deliberately slowing itself to reduce heat (symptom: the system gets very slow but stays on). Shutdown is the emergency cutoff (symptom: instant power-off). Throttling happens first; shutdown means throttling wasn't enough.

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5.4 Storage Failures: "No Boot Device"

Scenario: Monday morning. A user powers on their PC and gets: "No bootable device found" or "Reboot and select proper boot device." Friday it worked fine.

Step 1 — Identify. Ask: "Do you hear any clicking or grinding from the computer?" Clicking from a traditional hard drive is the sound of a dying drive — the read/write heads failing to find their position. Also ask about recent symptoms: was the system getting slower? Were files going missing? Those are early warnings.

HDD vs. SSD failure symptoms — this distinction shows up on the exam:

> EXAM TIP: "A user reports a clicking noise coming from the computer, and files are becoming corrupted. What is the MOST LIKELY cause?" — Failing hard disk drive. The clicking sound is exclusive to mechanical HDDs and is a classic exam cue. SSDs never click. If the scenario mentions grinding or ticking plus data corruption, the answer is always the HDD.

The troubleshooting sequence for boot failures:

1. Check BIOS/UEFI boot order. If someone left a USB drive plugged in, the system might be trying to boot from it. This is the #1 cause of "sudden" boot failures with no other symptoms — and the easiest fix.
2. Verify the drive is detected. Enter BIOS/UEFI setup and check whether the drive appears in the storage list. If it's not there: check the SATA data cable and power connector (reseat both). Try a different SATA port and cable.
3. Listen and observe. Clicking = dying HDD. Silence from an SSD that isn't detected = possibly dead controller.
4. Check S.M.A.R.T. status. If the drive is detected but the OS won't boot, S.M.A.R.T. data (viewable in BIOS or via diagnostic tools) may show reallocated sectors or other failure predictors.
5. Boot from recovery media. If the drive is detected but Windows won't start, the problem may be software (corrupted bootloader, not hardware). Boot from a USB installer and try Startup Repair before condemning the drive.

RAID failures — CompTIA expects you to know what happens when a RAID array degrades:

• RAID 0 (striping): One drive fails → ALL data lost. No redundancy. A RAID 0 failure is a data recovery scenario, not a rebuild scenario.
• RAID 1 (mirroring): One drive fails → system keeps running on the survivor. Replace the failed drive and the array rebuilds. This is the entire point of RAID 1.
• RAID 5 (striping with parity): One drive fails → array runs in degraded mode (slower, but functional). Replace and rebuild. Two drives fail → data lost.
• RAID 10 (mirror of stripes): Can survive one drive failure per mirrored pair.

> EXAM TIP: RAID questions test two things: (1) which levels survive a single-disk failure (everything except RAID 0), and (2) what to do when an array reports degraded. The answer is always: replace the failed drive and let the array rebuild — NOT "restore from backup" as the first step (though you should verify backups exist). Also know that RAID is not a backup — it protects against drive failure, not deletion, corruption, or ransomware.

Scenario — the degraded array: "Our file server is running very slowly, and the RAID controller is beeping." The beeping is the controller's audible alarm for a failed/degraded array. Step 1: identify which drive failed (controller software or blinking amber LED on the drive caddy). Step 2: verify you have a current backup BEFORE touching anything — a rebuild stresses the surviving drives, and a second failure during rebuild means total loss. Step 3: replace the failed drive with one of equal or larger capacity and let the rebuild complete. Do not reboot mid-rebuild.

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5.5 Memory Issues and the Blue Screen

Scenario: "My computer keeps showing a blue screen with a sad face, then restarts. It happens randomly — sometimes when I boot up, sometimes hours later."

The Blue Screen of Death (BSOD) is Windows' response to a critical error it can't recover from. The key diagnostic information is the stop code (e.g., MEMORY_MANAGEMENT, IRQL_NOT_LESS_OR_EQUAL, PAGE_FAULT_IN_NONPAGED_AREA) and the fact of randomness.

Random, intermittent crashes point to hardware — and RAM is the prime suspect:

1. Reseat the RAM. Power off, unplug, ground yourself, remove each DIMM, and reinsert firmly until the retention clips snap. Poorly seated RAM — especially after shipping or moving a PC — causes exactly this pattern.
2. Test one stick at a time. If there are multiple DIMMs, remove all but one and test. Swap through them. If the crashes stop with a particular stick removed, you've found the bad module.
3. Run a memory diagnostic. Windows Memory Diagnostic (built in) or MemTest86 (bootable, more thorough). Let it complete at least one full pass — a quick test can miss intermittent faults.
4. Check the slots. A bad DIMM slot on the motherboard produces the same symptoms as bad RAM. If a known-good stick fails in slot 2 but works in slot 1, the slot is the problem.
5. Verify compatibility. Mixing RAM speeds, voltages, or timings can cause instability. Check that all modules match the motherboard's supported specifications.

> EXAM TIP: For BSOD questions, look for the pattern. Random/inconsistent crashes = RAM. Crashes only during graphics-intensive tasks = GPU or overheating. Crashes with a specific stop code mentioning a driver file (.sys) = driver issue, not hardware. CompTIA will give you the pattern — match the pattern to the component. "MEMORY_MANAGEMENT" in the stop code is practically giving you the answer.

Insufficient RAM presents differently — not crashes, but slowness. Symptoms: heavy disk activity (the system thrashing as it pages to disk), applications freezing momentarily, "low memory" warnings. The fix is adding RAM, but the diagnostic step is checking Task Manager — if memory utilization is pinned at 90%+ during normal use, the system needs more.

POST beep codes deserve mention here too. If the system won't boot and emits beeps: one long, two short (or whatever pattern your BIOS uses) — memory failure is the most common cause of beep codes on startup. Consult the motherboard manual for the specific pattern. No display + beeping = check RAM first.

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5.6 Display Issues

Scenario: "I press the power button, the computer sounds like it's starting, but the monitor stays black."

No display at all — work through the chain: monitor power → cable → GPU → RAM → motherboard.

1. Is the monitor on? Check the monitor's power LED. Try the monitor's menu buttons — if the on-screen menu appears, the monitor itself works and the problem is the signal. This single test eliminates half the possibilities.
2. Check the cable. Reseat both ends. Try a different cable. Try a different port (HDMI vs. DisplayPort). Bent pins on VGA/DVI connectors were the classic cause; with digital connectors, look for a cable that's partially seated.
3. Check the input source. Monitors with multiple inputs sometimes switch to the wrong one. Cycle the input button.
4. Listen for POST. If the system beeps normally and you hear Windows startup sounds, the PC is booting fine — it's purely a display output issue. Focus on GPU, cable, monitor.
5. Test with integrated graphics. If the system has onboard video, remove the discrete GPU and connect to the motherboard output. If display returns, the GPU is the problem.
6. Reseat the GPU and RAM. A GPU that's worked loose from its PCIe slot (heavy cards sag over time) causes no-display. And remember: bad RAM also causes no display with beep codes.

Display artifacts (weird colors, lines, checkerboard patterns, garbled text) point to:

• Failing GPU — especially artifacts that appear in 3D applications or get worse as the card heats up
• Overheating GPU — check the card's fan
• Bad cable — usually shows as sparkles or intermittent dropouts rather than persistent artifacts
• Wrong refresh rate / resolution — if the image is distorted but stable, check display settings before suspecting hardware

> EXAM TIP: "A user reports distorted images and colored lines on the screen that worsen when playing games. What is the MOST LIKELY cause?" — Failing or overheating GPU. The "worsens under graphical load" pattern is the key. If instead the scenario described a flickering screen or "no signal" message, you'd think cable or monitor. Match the symptom pattern.

Flickering is usually:

• Loose cable (most common)
• Refresh rate mismatch
• Failing backlight/inverter on older LCDs (screen goes dim, not flickery — actually dimness is the backlight symptom)
• Nearby electromagnetic interference (rare with digital, was common with CRTs)

Dim display on a laptop specifically: if the image is barely visible (you can see it if you shine a flashlight at the screen), the backlight has failed. The LCD panel works — it's just not lit. This is a backlight/inverter issue, not a GPU issue. On modern LED-backlit laptops, it's usually the entire display assembly.

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5.7 Printer Problems

Printers generate a disproportionate share of helpdesk tickets, and CompTIA knows it. The exam focuses heavily on laser printers — know the imaging process and where each failure occurs.

The laser printing process (in order): Processing → Charging → Exposing → Developing → Transferring → Fusing → Cleaning. You need to map symptoms to stages:

> EXAM TIP: This table is gold for the exam. CompTIA asks "ghosting" and "toner not fused" questions constantly. Memorize: ghost images = cleaning/drum, toner rubs off = fuser. These two mappings alone will earn you points. Also know that the fuser is HOT (around 200°C/400°F) — always let it cool before servicing, and it's a common exam safety question.

Scenario — the ghosting printer: "Our laser printer prints fine on the first page, but there's a faint copy of the logo repeating further down each page." That's classic drum/cleaning failure. The drum isn't being fully cleaned between rotations, so residual toner from one revolution prints faintly on the next. Fix: replace the toner cartridge (most include the drum) or the drum unit separately. If it persists with a new cartridge, the fuser may be damaged.

Scenario — paper jams: "The printer jams every few pages." Don't just clear the jam — find the cause:

1. Check the paper. Wrong weight, damp paper (absorbs humidity and sticks), or an overfilled tray. Fan the paper before loading.
2. Inspect the rollers. Worn pickup rollers slip instead of gripping — they look shiny/smooth instead of matte. Clean with isopropyl alcohol; replace if worn.
3. Look for obstructions. A torn scrap from a previous jam lodged in the paper path causes repeat jams in the same spot. Note WHERE the jam occurs — same spot every time means an obstruction or a bad roller at that point.
4. Check the paper path settings. Envelopes or labels through the standard tray instead of the manual feed will jam.

Inkjet-specific issues:

• Clogged print heads — the #1 inkjet problem, especially after the printer sits unused. Run the cleaning cycle from the printer's utility. Don't run it ten times in a row — it wastes enormous ink. Two to three cycles, then print a test page.
• Streaky output — usually clogged nozzles; run alignment and cleaning.
• Ink not recognized — reseat the cartridge, clean the contacts.

Network printer issues:

• "Printer shows offline" — check the IP address. If the printer uses DHCP and its lease expired, it may have a new IP while workstations still point to the old one. Assign a static IP or DHCP reservation — this is the standard fix and a favorite exam answer.
• Print spooler crashes — restart the Print Spooler service. If it recurs, a corrupt print job is usually the cause; clear the spooler queue.

> EXAM TIP: For "network printer offline" scenarios, the exam wants you to check the printer's IP address first and assign static/DHCP reservation as the preventive fix. The methodology applies: the "theory" is IP address change, the "test" is printing a configuration page to verify the current IP, and the "preventive measure" is the reservation.

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5.8 Mobile Device Issues

Scenario: "My phone gets really hot and the battery drains in like two hours. It used to last all day."

Mobile troubleshooting follows the same methodology, but the components are sealed — so your tools are settings, not screwdrivers.

Rapid battery drain + overheating — these two symptoms together almost always mean the same thing: something is running the processor hard in the background.

1. Check battery usage stats (Settings → Battery). The culprit app is usually right there at the top. A single misbehaving app — often after a bad update — can pin the CPU.
2. Check for stuck processes: force-stop the offending app, or restart the phone (which clears more than people expect).
3. Look at signal strength. A phone struggling to hold a weak cellular signal boosts its radio power to maximum, which drains the battery fast and generates heat. If the drain only happens in certain locations, it's the signal, not the phone.
4. Screen brightness and refresh rate are the other big drains — but they don't cause overheating by themselves.

> EXAM TIP: CompTIA tests the "weak signal = battery drain" relationship. "A user's phone battery drains rapidly when at their rural home but lasts normally at the office. What is the MOST LIKELY cause?" — The phone expending extra power to maintain a weak cellular signal. This is a classic "question the obvious / consider environmental factors" question.

Common mobile symptoms and causes:

Swollen battery — if the phone's case is bulging or the screen is lifting, the lithium battery is swelling. This is a safety issue: do not charge it, do not puncture it, power it off. Swollen batteries can catch fire. This is one of the exam's safety questions — the correct action is to stop using the device and have the battery replaced by a qualified technician.

Broken screen vs. broken digitizer: If the display shows the image fine but touch doesn't work (or works in wrong spots), the digitizer layer failed — the LCD is fine. If there's no image, or black blotches and colored lines, the LCD itself is damaged. This distinction determines whether you replace just the digitizer or the full display assembly.

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5.9 Network Issues: "I Can't Get Online"

Scenario: "Nothing on the internet works. I can't open any websites."

This is the most common network ticket in existence. Run it methodically:

Step 1 — Identify: scope the problem.

• "Is it just your computer, or everyone?" If everyone is down, it's infrastructure (switch, router, ISP) — not the user's PC. This single question saves enormous time.
• "Is it all websites, or just one?" One site down = that site's problem, not yours.
• "Wired or wireless?" Narrows the troubleshooting domain immediately.
• "Did anything change?" New router, ISP visit, construction outside — changes are clues.

Step 2 — Theory, from most to least likely:

1. Physical layer (cable unplugged, Wi-Fi disconnected, airplane mode on)
2. Local configuration (wrong IP, APIPA address, DNS issue)
3. Local network device (switch port, router)
4. ISP / upstream outage

> EXAM TIP: The exam rewards checking the physical layer first — ALWAYS. "A user cannot access network resources. The technician should FIRST:" — the answer involves checking the cable connection, link lights, or Wi-Fi status. Never "reinstall the network driver" or "replace the NIC" as a first step. CompTIA's methodology demands outside-in, simple-to-complex.

The command-line toolkit — know these cold:

• ipconfig / ipconfig /all — Shows IP address, subnet mask, gateway, DNS. The FIRST command for any connectivity issue on Windows.
• 169.254.x.x (APIPA) = the PC couldn't reach a DHCP server. This is a huge diagnostic clue — it means Layer 1/2 might work (link is up) but DHCP failed. Check: is the DHCP server up? Is the cable actually connected to the right network? Is there a rogue DHCP issue?
• 0.0.0.0 = no address at all; the adapter may be disabled or failed.
• ping — Tests connectivity layer by layer:
• ping 127.0.0.1 (loopback) → tests the local TCP/IP stack. If this fails, the problem is the local machine's network stack — not the network.
• ping <gateway> → tests local network connectivity.
• ping 8.8.8.8 → tests internet connectivity bypassing DNS.
• ping google.com → tests DNS resolution AND connectivity.
• The pattern of what succeeds and what fails tells you exactly where the break is.
• tracert / traceroute — Shows each hop to the destination. If traffic dies at hop 1, it's your gateway. If it dies at hop 5, it's upstream — call the ISP with the trace as evidence.
• nslookup — Tests DNS specifically. If ping 8.8.8.8 works but ping google.com fails, it's DNS. Try nslookup google.com 8.8.8.8 to test against a specific server.

> EXAM TIP: CompTIA loves the "ping progression" question: "A technician can ping the loopback address and the default gateway but cannot ping an external IP address. Where is the problem?" — Beyond the local network (router/ISP side). Each successful ping eliminates a segment. Memorize the order: loopback → gateway → external IP → hostname (DNS). Also: APIPA (169.254.x.x) always means DHCP failure — the exam uses this as a direct cue.

Intermittent connectivity ("it works, then drops, then works again") is harder than total failure:

• Duplicate IP address — two devices with the same static IP take turns knocking each other off. Check for IP conflicts in the OS event logs.
• Failing cable — a cable with a marginal connection works until vibration, temperature, or traffic load breaks it temporarily. Swap the cable — it's the cheapest test.
• Overloaded switch port / broadcast storm — check switch port error counters.
• Wireless interference (covered in 5.10).
• DHCP lease issues — ipconfig /release then ipconfig /renew forces a fresh lease.

Slow network ("the internet is so slow"):

1. Run a speed test to quantify — "slow" is subjective; numbers aren't.
2. Check whether it's one device or all (scope again).
3. Look for bandwidth hogs: cloud backups, OS updates, streaming, malware.
4. Check the link speed — a gigabit NIC negotiated down to 100Mbps (bad cable, often) cuts throughput dramatically. The fix for a surprising number of "slow network" tickets is replacing a damaged Cat5e cable.
5. Wireless: check signal strength and channel congestion (5.10).

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5.10 Cables, Connectors, and Wireless Issues

Wired: the humble cable

Scenario: "My desktop gets 90 Mbps but my laptop on the same network gets 900 Mbps. Same speed test server."

The first suspect is the cable. Ethernet cables degrade in ways that don't cause total failure — just silent speed reduction:

• Damaged cable — a kink, crush, or stretched cable can break individual wire pairs. Gigabit needs all four pairs; if one pair fails, the NIC falls back to 100 Mbps (which only needs two pairs). The user sees "working but slow" — the classic symptom.
• Wrong cable category — Cat5 (not 5e) maxes at 100 Mbps. In older buildings, the in-wall wiring might be Cat5 while the patch cables are Cat6 — the chain is only as fast as its slowest link.
• Exceeding distance — 100 meters is the limit for twisted-pair Ethernet. Beyond that, signal degrades. (Fiber goes much farther.)
• Electromagnetic interference — running Ethernet parallel to power cables induces noise. Cross power lines at 90 degrees; maintain separation.

> EXAM TIP: Know your cable types and their speeds: Cat5e = 1 Gbps @ 100m, Cat6 = 1 Gbps @ 100m (10 Gbps @ 55m), Cat6a = 10 Gbps @ 100m. The exam asks "which cable for 10 Gbps over 80 meters?" — Cat6a (Cat6 only does 10 Gbps to 55m). Also know fiber connectors (LC, SC, ST) and that fiber is immune to EMI — "which cable for an environment with heavy electromagnetic interference?" is always fiber.

Link lights are your fastest physical diagnostic. No link light = no Layer 1 connection. Check: cable seated? Correct port? Try a different port on the switch. A link light that's on but no traffic flows suggests a higher-layer issue.

Wireless: the invisible complexity

Scenario: "The Wi-Fi works fine in the morning but gets terrible every afternoon around 2pm."

Time-patterned wireless problems scream interference. What's different at 2pm? The microwave in the break room (2.4 GHz), the neighboring office's network ramping up, Bluetooth devices, cordless phones.

The 2.4 GHz vs. 5 GHz vs. 6 GHz decision:

> EXAM TIP: "A user experiences wireless interference from nearby devices. Which band should the technician recommend switching to?" — 5 GHz (or 6 GHz if available). The 2.4 GHz band has only 3 non-overlapping channels (1, 6, 11) and shares spectrum with microwaves and Bluetooth. If the question mentions microwaves or Bluetooth specifically, the answer is to move to 5 GHz. Also know: 2.4 GHz travels farther through walls, so "the signal doesn't reach the back office" might mean switching DOWN to 2.4 GHz for range.

Channel overlap — on 2.4 GHz, use only channels 1, 6, or 11. Channels in between overlap and interfere with each other. A Wi-Fi analyzer app shows which channels neighbors use — pick the emptiest of the three.

Common wireless symptoms:

Weak signal troubleshooting order: reposition the access point (central, elevated, away from metal) → check for firmware updates → consider whether the client device's Wi-Fi is the problem (test with another device) → add an access point or mesh node. Don't start by buying new hardware.

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5.11 Master Symptom-to-Cause Reference

Use this table for rapid review. Cover the right column and quiz yourself.

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5.12 Chapter Review Questions

1. A user reports that their computer will not power on — no lights, no fans, no sounds. According to the troubleshooting methodology, what should the technician check FIRST?

• A. The motherboard for failed capacitors
• B. The wall outlet with a known-working device
• C. The RAM by reseating the modules
• D. The hard drive connections

2. A workstation shuts down whenever the user plays games but operates normally for web browsing and office applications. Which is the MOST LIKELY cause?

• A. Failing power supply
• B. Corrupted operating system
• C. Overheating CPU or GPU
• D. Insufficient RAM

3. A technician is troubleshooting a "no bootable device" error. The drive appears in the BIOS/UEFI storage list. What should the technician check NEXT?

• A. Replace the SATA cable
• B. The boot order in BIOS/UEFI
• C. Run a full memory diagnostic
• D. Replace the hard drive

4. A user hears a repetitive clicking noise from their desktop, and several files have become corrupted. What is the MOST LIKELY cause?

• A. Failing SSD
• B. Failing hard disk drive
• C. Loose CPU heatsink
• D. Faulty RAM

5. A RAID 5 array is reporting a degraded status after one drive failed. What should the technician do FIRST?

• A. Restore all data from backup immediately
• B. Replace the failed drive and allow the array to rebuild
• C. Convert the array to RAID 0
• D. Verify that a current backup exists, then replace the failed drive

6. A laser printer produces pages where the toner smears and rubs off when touched. Which stage of the laser printing process has failed?

• A. Charging
• B. Exposing
• C. Transferring
• D. Fusing

7. A network printer frequently shows as "offline" on user workstations, though it works after being restarted. What is the BEST long-term fix?

• A. Replace the printer's network cable
• B. Assign a static IP address or DHCP reservation to the printer
• C. Reinstall the printer drivers on all workstations
• D. Connect the printer via USB instead

8. A technician runs ipconfig on a Windows PC and sees the address 169.254.10.5. What does this indicate?

• A. The PC has a valid static IP address
• B. The PC could not contact a DHCP server
• C. The DNS server is misconfigured
• D. The network cable is unplugged

9. A technician can successfully ping 127.0.0.1 and the default gateway, but cannot ping 8.8.8.8. Where is the MOST LIKELY location of the problem?

• A. The local PC's TCP/IP stack
• B. The local network switch
• C. Beyond the local network (router or ISP)
• D. The DNS server

10. A user's phone battery drains in two hours and the phone feels hot, but only when they are at their rural home — it lasts all day at the office. What is the MOST LIKELY cause?

• A. A failing battery
• B. Too many background applications
• C. The phone boosting radio power to maintain a weak cellular signal
• D. An outdated operating system

11. A user reports that Wi-Fi performance degrades every afternoon when the office microwave is used. Which is the BEST solution?

• A. Move the wireless network to the 5 GHz band
• B. Increase the access point's transmit power
• C. Replace the microwave
• D. Add a second access point on the same channel

12. After resolving a printer jam and confirming the printer works, what should the technician do NEXT according to the troubleshooting methodology?

• A. Immediately close the ticket
• B. Replace the paper tray rollers preventively
• C. Verify full functionality, document the findings and actions, and note the cause
• D. Reboot the print server

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Answer Key

1. B — Always check external power first (methodology: identify the problem, question the obvious). The motherboard is the last suspect, not the first.

2. C — "Only under load" is the classic overheating pattern. The system is fine at idle because heat output is low; intensive tasks push temperatures past the shutdown threshold.

3. B — If the drive is detected in BIOS, the hardware connection works. The most common cause of a sudden "no bootable device" with a detected drive is the boot order (e.g., a USB drive left plugged in).

4. B — Clicking is exclusive to mechanical hard drives (the read/write heads failing). SSDs have no moving parts and never click. Corruption plus clicking = dying HDD.

5. D — RAID 5 survives one disk failure, but a rebuild stresses the remaining drives. Verify the backup exists FIRST (protect against a second failure during rebuild), then replace the drive. Jumping straight to replacement without confirming backups risks total data loss.

6. D — The fusing stage melts toner onto the page with heat and pressure. If toner rubs off, the fuser isn't reaching proper temperature — a failing fuser assembly.

7. B — The printer's DHCP lease expires and it gets a new IP, but workstations still point to the old one. A static IP or DHCP reservation prevents the address from changing — the standard preventive fix.

8. B — 169.254.x.x is APIPA (Automatic Private IP Addressing), assigned when the PC cannot reach a DHCP server. The cable may be fine (link is up); DHCP is the failure.

9. C — The ping progression eliminates segments: loopback OK means the local stack works; gateway OK means the local network works. Failure beyond the gateway points to the router or ISP.

10. C — Location-dependent drain is the key clue. A weak rural signal forces the phone's radio to maximum power, draining the battery and generating heat. At the office with strong signal, the problem disappears.

11. A — Microwaves operate at 2.4 GHz, directly interfering with 2.4 GHz Wi-Fi. Moving to the 5 GHz band avoids the interference entirely. Same-channel APs (D) would make it worse.

12. C — The methodology's final step: verify full system functionality, implement preventive measures, and document findings, actions, and outcomes. "Close the ticket" without documentation violates the methodology.