How to Use This Quick Reference
This independent Quick Reference is built for candidates preparing for the real CompTIA A+ Core 1 (220-1201) exam. Use it to review selection logic, symptoms, components, ports, and troubleshooting steps quickly.
Core 1 questions often ask you to:
- Identify a component, connector, cable, or port from a scenario.
- Choose the best first step in troubleshooting.
- Distinguish similar technologies: DNS vs. DHCP, M.2 vs. NVMe, WPA2 vs. WPA3, laser vs. inkjet, NAT vs. bridged VM networking.
- Recommend hardware or network changes for a user requirement.
- Interpret common symptoms without over-fixing the problem.
High-Yield Decision Traps
| Trap | Exam-safe distinction |
|---|
| M.2 means NVMe | M.2 is a form factor. M.2 drives can use SATA or NVMe/PCIe. |
| RAID is backup | RAID improves availability or performance; it does not replace backups. |
| USB-C means Thunderbolt | Thunderbolt may use USB-C, but not every USB-C port supports Thunderbolt. |
| 169.254.x.x means Internet outage | It usually means APIPA: the client did not get DHCP configuration. |
| DNS fixes IP assignment | DNS resolves names. DHCP assigns IP configuration. |
| 5 GHz is always better | 5 GHz is faster/cleaner at shorter range; 2.4 GHz penetrates farther and is more crowded. |
| MAC filtering is strong security | It is weak; MAC addresses can be spoofed. Use WPA2/WPA3 and strong credentials. |
| Snapshot is a backup | VM snapshots are short-term rollback points, not full backup strategy. |
| Laser streaks always mean toner | Streaks can be toner, drum, fuser, transfer roller, or contamination. |
| Slow PC always needs RAM | Check storage, malware, startup apps, overheating, CPU load, and failing hardware. |
Hardware Reference
Motherboard, CPU, Firmware, and Expansion
| Area | Know for the exam | Common troubleshooting clue |
|---|
| Form factor | ATX, microATX, Mini-ITX affect case size, slots, ports, and PSU fit. | Board does not line up with standoffs or I/O shield. |
| CPU socket | CPU must match motherboard socket and chipset support. | No POST after CPU upgrade. |
| Chipset | Determines supported CPU family, RAM type, expansion, storage, and I/O features. | Feature present on CPU but unavailable on board. |
| UEFI/BIOS | Firmware initializes hardware, stores boot order, exposes hardware settings. | Wrong boot order, disabled device, outdated firmware. |
| CMOS battery | Maintains firmware settings and clock when powered off. | Time/date resets; BIOS settings lost. |
| TPM | Hardware/firmware root for security features. | Security feature unavailable or device fails compliance check. |
| Secure Boot | Helps ensure trusted bootloaders. | Alternate OS or boot media may fail until settings are adjusted. |
| PCIe | Expansion bus for GPUs, NICs, storage adapters, capture cards. | Card needs correct slot, power, driver, and clearance. |
| Cooling | Heat sink, fan, thermal paste, airflow. | Random shutdowns, thermal throttling, fan noise. |
RAM Selection and Symptoms
| Concept | Practical reference |
|---|
| DIMM vs. SO-DIMM | DIMM is common in desktops/servers; SO-DIMM is common in laptops and small systems. |
| DDR generations | DDR versions are not physically interchangeable. Match board support. |
| Speed compatibility | RAM may run at the highest mutually supported speed of board/CPU/modules. |
| Capacity support | Check motherboard and OS support; avoid mixing unsupported sizes or types. |
| Dual-channel | Install matched modules in correct paired slots for performance. |
| ECC | Error-correcting memory; common in workstations/servers, requires platform support. |
| Symptoms of bad RAM | BSOD/kernel panic, random reboots, application crashes, failed memory diagnostics, no POST. |
Storage Selection Matrix
| Storage type | Choose when | Strengths | Limitations / traps |
|---|
| HDD | Low-cost bulk storage, archives, secondary drive. | High capacity per cost. | Mechanical failure, slower latency, vibration sensitivity. |
| SATA SSD | General PC upgrade, older systems, predictable compatibility. | Much faster than HDD; simple replacement path. | Limited by SATA interface. |
| NVMe SSD | High-performance boot/application drive. | Very low latency; PCIe performance. | Requires compatible M.2/PCIe support; heat may matter. |
| External USB drive | Portable backup, transfer, offline storage. | Easy and removable. | Can be lost, damaged, or disconnected. |
| NAS | Shared storage for multiple users/devices. | Centralized access, often supports RAID and permissions. | Network-dependent; still needs backup. |
| Optical drive | Legacy media, archival discs, installation media. | Useful for older environments. | Less common; slower and lower capacity. |
RAID Quick Reference
| RAID level | Minimum drives | Main purpose | Fault tolerance | Trap |
|---|
| RAID 0 | 2 | Performance/striping | None | One failed drive can lose array data. |
| RAID 1 | 2 | Mirroring | Can survive one drive failure in a pair | Capacity is reduced by mirroring. |
| RAID 5 | 3 | Striping with parity | Can survive one drive failure | Rebuild stress can expose other failures. |
| RAID 10 | 4 | Mirrored stripes | Good performance and redundancy | Requires more drives; not the same as RAID 0+1 in all failure cases. |
Power and Internal Connectors
| Connector/component | Used for | Exam clue |
|---|
| 24-pin ATX | Main motherboard power. | System will not power correctly if not seated. |
| 4/8-pin CPU power | CPU power near socket. | Fans may spin but system may not POST if missing. |
| PCIe power | Dedicated GPU or high-power expansion card. | GPU powers on partially or reports insufficient power. |
| SATA data | Connects SATA drives to motherboard. | Thin data cable; one drive per port. |
| SATA power | Powers SATA drives. | Wider power connector from PSU. |
| Molex | Legacy peripheral power. | Older fans/drives/adapters. |
| Front-panel headers | Power switch, reset, LEDs, audio, USB. | Case buttons or front USB/audio do not work. |
| Fan headers | CPU/system fans. | Incorrect header can trigger fan warnings. |
External Ports and Connectors
| Connector | Carries | Typical use | Trap |
|---|
| USB-A | Data/power | Keyboards, mice, flash drives. | Orientation-specific. |
| USB-C | Data/power/video depending on support | Modern laptops, phones, docks. | Connector shape does not guarantee protocol/features. |
| Thunderbolt | High-speed data, video, docks, storage | Docking stations, external GPUs, displays. | Often uses USB-C connector but requires Thunderbolt support. |
| HDMI | Digital audio/video | TVs, monitors, projectors. | Common for consumer displays. |
| DisplayPort | Digital audio/video | PCs, monitors, daisy-chaining in supported setups. | Common in business/PC displays. |
| VGA | Analog video | Legacy projectors/monitors. | No audio; analog quality issues. |
| DVI | Digital/analog variants | Older monitors. | Different pin layouts and capabilities. |
| RJ-45 | Ethernet | Wired LAN. | Looks larger than RJ-11. |
| RJ-11 | Telephone/DSL | Phone lines. | Not Ethernet. |
| 3.5 mm audio | Analog audio | Headsets, speakers, microphones. | Combo jacks may need TRRS support. |
Display and Peripheral Issues
| Symptom | Likely causes | First checks |
|---|
| No display | Power, cable, input source, GPU, RAM, monitor failure. | Verify power/input, reseat cable, test known-good monitor/cable. |
| Dim laptop screen | Brightness, backlight, display cable, older inverter, panel failure. | Adjust brightness, external display test. |
| Flicker/artifacts | Cable, refresh rate, GPU driver, overheating GPU, failing monitor. | Reseat/replace cable, check temperature, update/rollback driver. |
| Touchscreen inaccurate | Calibration, driver, digitizer damage. | Clean screen, recalibrate, check driver. |
| Keyboard keys fail | Debris, liquid damage, loose ribbon cable, keyboard failure. | External keyboard test. |
| Mouse/touchpad erratic | Dirty sensor, surface issue, driver, palm rejection, battery. | Clean/test on different surface; check settings. |
Mobile and Laptop Reference
Laptop Field-Service Items
| Component | What to remember |
|---|
| Battery | Use compatible replacement; swollen batteries are safety issues. |
| RAM | Often SO-DIMM; some systems have soldered RAM. |
| Storage | May be 2.5-inch SATA, M.2 SATA, or M.2 NVMe. |
| Wi-Fi/Bluetooth card | Internal antenna leads must be reconnected correctly. |
| Keyboard | Often ribbon-cable connected; model-specific replacement. |
| Screen assembly | Panel, bezel, hinges, webcam, microphone, Wi-Fi antennas may be integrated. |
| DC jack | Loose/broken charging port can mimic bad adapter or battery. |
| Cooling assembly | Dust, failed fan, poor thermal paste cause throttling/shutdowns. |
Mobile Connectivity and Sync
| Feature | Use | Troubleshooting clue |
|---|
| Cellular | Carrier network data/voice. | Check signal, SIM/eSIM, APN/carrier settings, airplane mode. |
| Wi-Fi | Local network/Internet. | Forget/rejoin network, verify password, DHCP, captive portal. |
| Bluetooth | Short-range peripherals. | Pairing mode, distance, battery, interference, remove/re-pair. |
| NFC | Tap-to-pair, mobile payments, badges. | Very short range; case or disabled setting can interfere. |
| Hotspot/tethering | Share mobile data to other devices. | Carrier plan, battery drain, data limits, Wi-Fi password. |
| GPS/location | Navigation, device location. | Permissions, indoor reception, battery-saving mode. |
| Cloud sync | Contacts, photos, files, settings. | Account sign-in, storage availability, network, sync toggles. |
| Local sync | Cable or local application sync. | Cable quality, trust prompt, drivers, app version. |
Mobile Symptoms
| Symptom | Likely cause | Best first actions |
|---|
| Rapid battery drain | Bad battery, weak signal, background apps, high brightness, GPS/Bluetooth. | Check battery usage, disable unnecessary services, test charger. |
| Won’t charge | Cable, adapter, port debris/damage, battery, charging IC. | Try known-good charger/cable, inspect port carefully. |
| Overheating | Heavy app, poor ventilation, battery fault, direct sun, failing hardware. | Close apps, remove case, cool down safely. |
| No Bluetooth pairing | Device not discoverable, already paired, low battery, compatibility. | Reboot, forget pairing, pair again. |
| App crashes | App bug, OS version, storage full, corrupted cache/data. | Update app/OS, clear cache, reinstall if needed. |
| No mobile data | Airplane mode, SIM/eSIM issue, APN/carrier outage, plan issue. | Toggle data, check SIM/eSIM, verify carrier settings. |
Networking Reference
Core Network Services and Devices
| Item | Function | Choose/identify when |
|---|
| Modem/ONT | Connects premises to ISP medium. | Cable/DSL/fiber handoff issue. |
| Router | Routes between networks; often does NAT and DHCP in SOHO. | Need default gateway or Internet sharing. |
| Switch | Connects devices within a LAN using MAC addresses. | Need more wired LAN ports. |
| Wireless AP | Provides Wi-Fi access to wired network. | Need wireless coverage, not routing. |
| Firewall | Allows/blocks traffic based on rules. | Need traffic filtering/security boundary. |
| UTM/security appliance | Combines firewall and security services. | Need consolidated gateway filtering. |
| Patch panel | Terminates structured cabling. | Cable management in wiring closet. |
| PoE injector/switch | Sends power over Ethernet to supported devices. | APs, IP phones, cameras without local power. |
| NAS | Network file storage. | Shared files/backups/media on LAN. |
| Repeater/extender | Extends signal coverage. | Dead zones; may reduce performance depending on design. |
IPv4 Address Types
| Address/range | Meaning |
|---|
| 127.0.0.1 | Loopback; tests local TCP/IP stack. |
| 169.254.x.x | APIPA/link-local; DHCP address was not obtained. |
| 10.x.x.x | Private IPv4 range. |
| 172.16.x.x to 172.31.x.x | Private IPv4 range. |
| 192.168.x.x | Private IPv4 range; common SOHO LANs. |
| Default gateway | Router IP used to reach other networks. |
| Subnet mask | Defines local network portion of IP address. |
| DNS server | Resolves names to IP addresses. |
| DHCP server | Automatically assigns IP configuration. |
\[
\text{Usable IPv4 hosts per typical subnet} = 2^{\text{host bits}} - 2
\]
| CIDR | Mask | Typical usable hosts |
|---|
| /30 | 255.255.255.252 | 2 |
| /29 | 255.255.255.248 | 6 |
| /28 | 255.255.255.240 | 14 |
| /27 | 255.255.255.224 | 30 |
| /26 | 255.255.255.192 | 62 |
| /25 | 255.255.255.128 | 126 |
| /24 | 255.255.255.0 | 254 |
| /16 | 255.255.0.0 | 65,534 |
| /8 | 255.0.0.0 | 16,777,214 |
Common Ports and Protocols
| Port | Protocol/service | Secure? | Exam cue |
|---|
| 20/21 | FTP | No | Legacy file transfer; control/data channels. |
| 22 | SSH / SFTP | Yes | Secure remote shell; SFTP uses SSH. |
| 23 | Telnet | No | Legacy remote shell; avoid when security matters. |
| 25 | SMTP | Usually no by default | Mail transfer between servers. |
| 53 | DNS | Varies | Name resolution; UDP common, TCP also used. |
| 67/68 | DHCP | No | Automatic IP configuration. |
| 69 | TFTP | No | Simple file transfer, network boot/configs. |
| 80 | HTTP | No | Web traffic without TLS. |
| 110 | POP3 | No | Downloads mail from mailbox. |
| 123 | NTP | No/varies | Time synchronization. |
| 143 | IMAP | No | Mail access with server-side folders. |
| 161/162 | SNMP | Varies | Network monitoring and traps. |
| 389 | LDAP | No by default | Directory queries. |
| 443 | HTTPS | Yes | Web traffic over TLS. |
| 445 | SMB/CIFS | Varies | Windows file/printer sharing. |
| 465/587 | SMTPS/submission | Yes/STARTTLS commonly | Authenticated mail submission. |
| 636 | LDAPS | Yes | LDAP over TLS. |
| 993 | IMAPS | Yes | Secure IMAP. |
| 995 | POP3S | Yes | Secure POP3. |
| 3389 | RDP | Encrypted but protect carefully | Remote Desktop. |
Wireless Standards and Selection
| Standard/concept | Practical reference |
|---|
| 802.11a | 5 GHz; older. |
| 802.11b/g | 2.4 GHz; older; more interference. |
| 802.11n | 2.4 GHz and/or 5 GHz; MIMO introduced broadly. |
| 802.11ac | 5 GHz; common Wi-Fi 5. |
| 802.11ax | Wi-Fi 6/6E family; efficiency improvements; may use 2.4, 5, and 6 GHz depending on device/AP support. |
| 2.4 GHz | Better range/wall penetration; more congestion; fewer non-overlapping channels. |
| 5 GHz | Higher throughput, less crowded, shorter range. |
| 6 GHz | Cleaner spectrum where supported; shorter range; requires compatible clients/APs. |
| WPA2 | Common secure Wi-Fi option when configured with AES. |
| WPA3 | Newer security improvements where supported. |
| Enterprise mode | Uses 802.1X/RADIUS credentials. |
| Personal mode | Uses pre-shared key/passphrase. |
| WPS | Convenience pairing; often disabled for security. |
| Captive portal | Web-based login page, common in guest/public networks. |
SOHO Router / AP Setup Checklist
- Connect modem/ONT to router WAN/Internet port.
- Configure LAN IP range and DHCP scope.
- Set SSID, security mode, and strong passphrase.
- Prefer WPA3 where all clients support it; otherwise use strong WPA2 configuration.
- Disable WPS unless specifically required.
- Change default administrator credentials.
- Update firmware from trusted vendor source.
- Configure guest network isolation if guests need Internet only.
- Use port forwarding only when required; document every rule.
- Place AP centrally and away from interference.
- Back up configuration after successful setup.
Cabling and Termination
| Cable/connector | Use | Notes |
|---|
| Cat 5e | Ethernet LAN. | Common for gigabit-class LANs. |
| Cat 6 / 6a | Ethernet LAN with better performance/headroom. | Better for newer structured cabling. |
| UTP | Unshielded twisted pair. | Common office/home Ethernet. |
| STP | Shielded twisted pair. | Helps in high-interference environments; grounding matters. |
| Plenum cable | Air-handling spaces. | Required by building design/code contexts; know the term. |
| Coaxial / F-type | Cable Internet/TV. | Screws onto cable modem/TV equipment. |
| Fiber | Long-distance/high-speed links. | Uses light; not affected by EMI. |
| LC/SC/ST | Fiber connectors. | Recognize connector types by scenario/image. |
| Straight-through | Standard Ethernet patching. | Common device-to-switch connections. |
| Crossover | Connects similar older Ethernet devices. | Auto-MDI-X reduces need on modern devices. |
| Rollover/console | Device management console. | Used for network device console access. |
| T568A/T568B | Wiring pinout standards. | Use one consistently; crossover uses different ends. |
Network Command Triage
Use commands to isolate where connectivity fails: local stack, NIC, gateway, DNS, or remote route.
ipconfig /all
ping 127.0.0.1
ping <own-ip-address>
ping <default-gateway>
ping <known-good-ip>
nslookup <fqdn>
tracert <fqdn>
| Result | Likely meaning |
|---|
| Cannot ping 127.0.0.1 | Local TCP/IP stack or host firewall issue. |
| Cannot ping own IP | NIC/IP configuration problem. |
| Cannot ping gateway | Local LAN, Wi-Fi, cable, VLAN, or gateway issue. |
| Can ping IP but not name | DNS problem. |
| Trace stops after gateway | Upstream routing/ISP/firewall issue possible. |
| IP is 169.254.x.x | DHCP failure or unreachable DHCP server. |
Printers and Imaging
Printer Type Selection
| Printer type | Choose when | Consumables | Common issues |
|---|
| Laser | High-volume text, office use, fast output. | Toner, drum, fuser, transfer components. | Streaks, ghosting, jams, fuser issues. |
| Inkjet | Photo/color use, lower device cost. | Ink cartridges, printhead. | Clogged nozzles, streaks, wet/smeared output. |
| Thermal | Receipts, labels, low-maintenance point-of-sale. | Thermal paper or ribbon depending type. | Faded output, wrong paper, heat sensitivity. |
| Impact | Multipart forms, harsh/legacy environments. | Ribbon, tractor-feed paper. | Noisy, printhead/ribbon issues. |
| 3D printer | Prototyping and physical models. | Filament/resin, build surface. | Adhesion, clogged nozzle, calibration/leveling. |
| Virtual printer | Print to PDF/XPS or redirect output. | None physical. | Driver/default printer/output path confusion. |
Laser Printing Process
| Step | What happens | Related symptom |
|---|
| Processing | Printer receives and prepares job. | Job stuck, wrong driver, memory issue. |
| Charging | Drum receives uniform charge. | Background shading or uneven image. |
| Exposing | Laser writes image to drum. | Missing/incorrect image. |
| Developing | Toner adheres to charged image. | Faded print, toner distribution issue. |
| Transferring | Toner moves to paper. | Repeating defects, transfer roller issues. |
| Fusing | Heat/pressure bonds toner to paper. | Smearing if toner is not fused. |
| Cleaning | Residual toner removed. | Ghosting or repeated marks. |
Printer Troubleshooting Matrix
| Symptom | Likely cause | Best checks |
|---|
| Paper jam | Worn rollers, wrong paper, debris, tray alignment. | Remove jam fully, inspect path, verify media type. |
| Faded laser output | Low toner, bad toner cartridge, density setting. | Shake/replace toner, check settings. |
| Toner smears | Fuser problem or wrong media. | Check fuser, media type, printer temperature readiness. |
| Ghost images | Drum/fuser/cleaning issue. | Replace affected consumable. |
| Inkjet streaks | Clogged nozzle, low ink, dirty printhead. | Run cleaning/calibration; replace cartridge if needed. |
| Thermal blank output | Paper loaded backward, wrong paper, failed printhead. | Verify thermal paper orientation. |
| Impact faint output | Worn ribbon or printhead. | Replace ribbon; inspect printhead. |
| Incorrect printer output | Wrong driver, wrong default printer, bad application setting. | Verify driver and print queue. |
| Network printer offline | IP change, Wi-Fi issue, print spooler, firewall. | Ping printer, check IP/reservation, restart spooler/device. |
Virtualization and Cloud
Virtualization Concepts
| Concept | What it means | Exam cue |
|---|
| Hypervisor | Software/firmware that runs virtual machines. | Required to host VMs. |
| Type 1 hypervisor | Runs directly on hardware. | Server/datacenter virtualization. |
| Type 2 hypervisor | Runs on top of a host OS. | Desktop lab/testing VM. |
| Guest OS | OS inside a VM. | Needs virtual hardware and drivers/tools. |
| Virtual switch | Connects VMs to virtual/physical networks. | VM network design. |
| Snapshot/checkpoint | Captures VM state for rollback. | Short-term change safety, not backup. |
| Clone/template | Creates repeatable VM copies. | Rapid deployment/testing. |
| Resource allocation | CPU, RAM, storage assigned to VM. | Over-allocation causes performance issues. |
| Sandboxing | Isolated environment for testing. | Reduce risk to production host/network. |
VM Network Modes
| Mode | VM can access | Other devices can access VM? | Use when |
|---|
| NAT | External networks through host translation. | Usually not directly. | Simple Internet access for lab VM. |
| Bridged | Same LAN as host. | Yes, like a physical device. | VM must be reachable on LAN. |
| Host-only | Host and isolated VMs. | No external LAN by default. | Isolated testing. |
| Internal/private | Only VMs on same virtual network. | No host or LAN unless configured. | Multi-VM isolated lab. |
Cloud Models and Service Selection
| Model | You manage more | Provider manages more | Choose when |
|---|
| On-premises | Hardware through applications. | Little/none. | Full control, local constraints, existing infrastructure. |
| IaaS | OS, apps, data; sometimes network config. | Physical hardware and virtualization. | Need VM-like control without owning hardware. |
| PaaS | Application code/data/config. | OS, runtime platform, scaling components. | Developers need platform without server maintenance. |
| SaaS | User settings and data usage. | Application and infrastructure. | Need ready-to-use software. |
| Cloud characteristic | Meaning |
|---|
| Rapid elasticity | Resources can scale up/down quickly. |
| Measured service | Usage is metered/monitored. |
| Resource pooling | Shared provider infrastructure serves multiple customers. |
| On-demand self-service | Users/admins can provision without manual provider interaction. |
| Broad network access | Services are reachable over networks by supported clients. |
| High availability | Design goal to keep services accessible despite component failures. |
| File synchronization | Data replicated between device and cloud/service. |
Troubleshooting Methodology
CompTIA-Style Troubleshooting Flow
| Step | What to do | Exam behavior |
|---|
| 1. Identify the problem | Gather information, question user, identify changes, duplicate issue if possible. | Do not jump to replacement before facts. |
| 2. Establish a theory | Start with obvious/common causes. | Loose cable, power, wrong input, Wi-Fi disabled, low toner. |
| 3. Test the theory | Confirm or revise theory. | If theory fails, establish a new one. |
| 4. Establish a plan and implement | Plan fix, consider impact, apply solution. | Avoid risky changes without backup/approval context. |
| 5. Verify full functionality | Confirm issue resolved and preventive measures applied. | Test with user workflow, not just component power-on. |
| 6. Document findings | Record symptoms, cause, fix, and follow-up. | Documentation is a valid final step. |
Hardware Symptom Matrix
| Symptom | Likely cause | Quick isolation |
|---|
| No power | PSU, outlet, cable, switch, motherboard short. | Test outlet/cable, check PSU switch, minimal boot. |
| Fans spin, no POST | RAM, CPU power, motherboard, GPU, firmware. | Reseat RAM/GPU, check CPU power, beep/LED codes. |
| Random shutdown | Overheating, PSU, failing board, battery. | Check temperatures, fans, dust, PSU load. |
| Burning smell | Electrical failure, overheated component. | Power off immediately; inspect safely. |
| Clicking drive | Mechanical HDD failure. | Stop unnecessary use; back up/recover if possible. |
| Slow storage | HDD fragmentation, failing disk, full disk, background tasks. | Check SMART/health, free space, disk activity. |
| BSOD/kernel panic | Driver, RAM, storage, overheating, OS issue. | Note error, check recent changes, diagnostics. |
| Date/time resets | CMOS battery. | Replace battery and reset firmware settings. |
| System beeps | POST hardware fault. | Interpret vendor beep/LED codes. |
Network Symptom Matrix
| Symptom | Likely cause | First checks |
|---|
| No link light | Cable, port, NIC, switch power. | Reseat cable, test known-good cable/port. |
| Connected, no Internet | Gateway, DNS, upstream ISP, captive portal. | Check IP/gateway/DNS; ping gateway then known IP. |
| APIPA address | DHCP unreachable. | Check DHCP server/router, VLAN, Wi-Fi association. |
| Can access IP not names | DNS issue. | Check DNS server configuration and resolution. |
| Slow Wi-Fi | Distance, interference, congestion, band selection. | Move closer, change band/channel, reduce interference. |
| Intermittent connection | Cable damage, weak Wi-Fi, duplex/speed mismatch, power saving. | Test wired path, replace cable, check logs/settings. |
| One device affected | Client configuration/NIC/driver. | Compare with working device on same network. |
| All devices affected | Router/switch/AP/ISP/power. | Check infrastructure and upstream connection. |
Safety and Handling
| Situation | Safe practice |
|---|
| Inside PC | Power down, unplug when appropriate, use ESD precautions. |
| ESD-sensitive parts | Use antistatic strap/mat or proper grounding. |
| Power supplies | Do not open PSU; capacitors can retain charge. |
| Laser printer | Let fuser cool; toner is fine particulate. |
| Batteries | Do not puncture/swollen batteries; recycle properly. |
| CRT/legacy high voltage | Avoid internal service unless trained. |
| Liquids | Power off, disconnect, dry/inspect before reapplying power. |
| Lifting equipment | Use proper lifting technique or assistance. |
| Tool | Use |
|---|
| Phillips/flathead/Torx drivers | Open cases, replace components. |
| ESD strap/mat | Protect components from electrostatic discharge. |
| Multimeter | Test voltage, continuity, basic electrical faults. |
| PSU tester | Quick PSU output check. |
| Cable tester | Validate Ethernet cable wiring/continuity. |
| Loopback plug | Test port transmit/receive function. |
| Toner probe | Trace cable runs. |
| Punchdown tool | Terminate wires on patch panels/keystone jacks. |
| Crimper | Attach modular connectors. |
| Wi-Fi analyzer | Check signal strength, channel congestion. |
| Compressed air | Remove dust; hold fans to prevent overspinning. |
| Thermal paste | Reinstall CPU heat sink properly. |
| Known-good cable/device | Fast isolation by substitution. |
Final Review Checklist
Before moving on, make sure you can answer these quickly:
- What symptom points to DHCP failure?
- Which service resolves names to IP addresses?
- Which ports are used by DNS, DHCP, HTTPS, SMB, SSH, and RDP?
- Why is RAID not a backup?
- When would you choose bridged instead of NAT networking for a VM?
- What is the order of the laser printing process?
- Which Wi-Fi band has better range, and which typically offers higher throughput?
- What is the difference between M.2, SATA, and NVMe?
- Which printer type is best for multipart forms?
- What should you do before replacing hardware in a troubleshooting scenario?
Practical Next Step
Use this Quick Reference as a checklist, then drill scenario-based practice questions for CompTIA A+ Core 1 (220-1201). Focus especially on troubleshooting order, port recognition, hardware selection, printer symptoms, and network isolation steps.