CompTIA A+ guideCore 1 skills
A+ Hardware and Network Troubleshooting: Symptoms and First Checks
Hardware and Network Troubleshooting is the largest Core 1 domain at 28%. Use these symptom, first-check, and likely-cause tables for power, drives and RAID, displays, mobile devices, and networks.
Short answer
Hardware and Network Troubleshooting is 28% of A+ Core 1 (220-1201), the largest domain. Its objectives are all scenario-based: motherboards, RAM, CPUs, and power; drives and RAID; video and displays; mobile devices; networks; and printers. For each symptom, know the safe first check and the most likely cause. Questions usually reward the simple, testable step before a part replacement.
What domain 5 covers and how to use these tables
Hardware and Network Troubleshooting is 5.0 in the 220-1201 objectives, version 3.0, and it carries 28% of Core 1, the largest share. Every objective in it starts with "given a scenario." The six areas are motherboards, RAM, CPUs, and power (5.1); drives and RAID (5.2); video, projectors, and displays (5.3); mobile devices (5.4); networks (5.5); and printers (5.6). Printers have their own guide, A+ printers.
Each table pairs a symptom from the objectives with a realistic first check and the cause that check usually points to. The first check is the step a scenario question tends to reward: cheap, safe, and testable. The cause column is a common culprit, not the only one. The ordering logic behind "first check" is explained in the troubleshooting methodology guide.
Two habits before any first check
- Safety first. Core 2's safety objective lists ESD straps and mats, and disconnecting power before you repair a PC. A burning smell or visible smoke means power off and unplug before anything else.
- Protect the data when the drive is the suspect. Grinding, clicking, and S.M.A.R.T. warnings are reasons to back up first. Diagnose afterward.
Power, motherboard, RAM, and CPU (5.1)
| Symptom | First check | Likely cause |
|---|---|---|
| No power: no lights, no fans | Outlet, power strip switch, power cord, and the PSU's own switch | Power not reaching the PC, then a failed power supply |
| POST beeps | Count the pattern and look it up in the motherboard or system maker's documentation | Beep codes differ by firmware vendor. RAM and video are frequent culprits. |
| Blank screen, but fans spin | Monitor power and input, the video cable, and whether the board has POSTed | Display path, or a failed POST |
| Random shutdowns or overheating | Vents, fans, and dust, and the temperature reading in BIOS/UEFI | Cooling failure or a dried-out thermal interface |
| Proprietary crash screens, such as a Windows stop error | Recent driver or hardware changes, and a memory test | Faulty RAM, drivers, or overheating |
| Sluggish performance, application crashes | Temperatures and resource use before you suspect hardware | Thermal throttling, insufficient RAM, or failing storage |
| Inaccurate system date and time after power-off | The CMOS battery | A depleted CMOS battery |
| Burning smell | Power off and unplug immediately | A failing power supply or component |
| Unusual noise | Whether it is a fan or a drive | A worn fan bearing, or a drive. See 5.2. |
| Capacitor swelling | Inspect the board with power disconnected | A failing motherboard. Replace it rather than attempt a repair. |
Walk-through: capacitor swelling. An office PC reboots at random. Event logs show nothing useful. With power disconnected and an ESD strap on, the technician sees two capacitors near the CPU socket with domed tops. That is a physical finding, not a theory. The fix is a replacement board, or a replacement PC if the board is not worth sourcing. Reinstalling Windows would waste the afternoon.
Drives and RAID (5.2)
| Symptom | First check | Likely cause |
|---|---|---|
| Grinding or clicking sounds | Back up immediately, if the drive still reads | A mechanical failure in a hard disk drive |
| S.M.A.R.T. failure warning | Back up, then plan the replacement | The drive is predicting its own failure |
| "Bootable device not found" | Boot order in BIOS/UEFI, then whether the drive is detected at all | A wrong boot order, a disconnected drive, or a failed drive |
| Missing drive in the OS | Disk Management, then cabling and power to the drive | A drive that is not initialized, has no letter, or is not connected |
| Extended read/write times, low IOPS | Free space and drive health, and for an array, whether it is degraded | A failing drive, or an array running in a degraded state |
| Data loss or corruption | chkdsk on the volume, after a backup | File system errors, or a failing drive |
| RAID failure, LED status indicators, audible alarm | The controller or array management tool, to see which member failed | A failed member disk in a redundant array |
| Array missing | The storage mode in BIOS/UEFI and the controller's own utility | A changed controller setting, or more failures than the RAID level tolerates |
Microsoft's chkdsk reference notes that /f fixes file system errors and /r also locates bad sectors and recovers readable information. Both need the volume locked and administrator rights.
Walk-through: array missing. A small office server boots, but its RAID 5 data volume is gone. Someone updated the server's UEFI firmware over the weekend, and the update reset the firmware settings. The first check is the storage controller mode in UEFI. If it now says AHCI instead of RAID, set it back before touching any disk. Initializing or "repairing" the disks in the OS first could destroy the array. RAID levels and how many failures each one tolerates are in the RAID and storage guide.
Video, projector, and display (5.3)
| Symptom | First check | Likely cause |
|---|---|---|
| No picture, or the wrong picture | The input source on the monitor or projector | The incorrect input source is selected |
| Flashing screen, or color problems | Reseat or swap the cable and adapter | Physical cabling issues |
| Fuzzy image | Whether the resolution matches the display's native resolution | A non-native resolution |
| Sizing issues, distorted image | Display scaling and resolution settings | Wrong scaling or aspect ratio |
| Dim image | Brightness settings and power-saving modes | Settings first, then a failing backlight |
| Dead pixels | Whether the pixels stay dark or stuck on every image | A panel defect |
| Display burn-in | Whether a ghost of a static image persists | Long display of static content |
| Projector shuts down intermittently | Air filter, vents, and fan | Overheating |
| Projector bulb will not light | Lamp hours and status indicator | A burnt-out bulb |
| No audio over HDMI or DisplayPort | The selected playback device in the OS | Audio routed to the wrong output |
Mobile devices (5.4)
| Symptom | First check | Likely cause |
|---|---|---|
| Poor battery health | The device's battery health readout and charge habits | An aging battery |
| Swollen battery | Stop using the device. See the walk-through below. | Battery failure. This is a safety issue. |
| Improper charging | Try a known-good cable and charger, and inspect the port for debris or damage | A cable, adapter, or physically damaged port |
| Poor or no connectivity | Airplane mode and the Wi-Fi, cellular, and Bluetooth toggles | Settings, then the antenna or radio |
| Liquid damage | Power the device off and do not charge it | Corrosion or a short |
| Overheating | Running apps, case, environment, and charging while in use | Workload or a failing battery |
| Digitizer issues, cursor drift | Clean the screen, remove the screen protector, restart | A damaged or poorly calibrated digitizer |
| Unable to install new applications | Free storage and OS version requirements | Low storage, or incompatibility |
| Stylus does not work | Pairing and the stylus battery | Pairing or power |
| Degraded performance, unexpected behavior | Storage, updates, and recently installed apps | Resource exhaustion, or malware |
Walk-through: a swollen battery. A user says her laptop's trackpad now clicks by itself and the case no longer sits flat. That is a swollen battery pushing on the trackpad from below. Dell's guidance for a swollen lithium-ion battery is to stop using the laptop, disconnect the AC adapter, and let the battery drain. Do not crush, puncture, or bend the battery, and do not use tools to force it out. Contact the manufacturer's support for replacement, and return the battery or take it to an approved recycler. The A+ answer to "what next?" is never to keep using the laptop until the replacement arrives.
Network (5.5)
| Symptom | First check | Likely cause |
|---|---|---|
| Limited connectivity | The client's IP settings. A 169.254.x.x address means no DHCP reply. | DHCP is unreachable, or the link is down |
| Intermittent wireless connectivity | Signal strength and channel use with a Wi-Fi analyzer | Distance, obstacles, or channel congestion |
| External interference | Analyzer readings on 2.4 GHz, and whether the problem follows a device | Shared 2.4 GHz spectrum. Move to 5 GHz, or change the channel. |
| Slow network speeds | Link speed on the NIC, then congestion | A bad cable or port negotiating a low speed, or saturation |
| High latency, jitter, poor VoIP quality | Whether the problem coincides with heavy traffic, and QoS settings | Congestion without QoS for voice |
| Port flapping | The switch port's link status history, then the cable and NIC | A bad cable, connector, NIC, or switch port |
| Authentication failures | Credentials, the security type the client expects, and whether one user or everyone is failing | A wrong passphrase, a mismatched security setting, or an authentication server problem |
| Intermittent internet connectivity | Whether the LAN stays up while the internet drops | The ISP link or the modem, not the LAN |
Microsoft's Wi-Fi guidance backs the interference rows. 2.4 GHz is more congested than 5 GHz, and channels 1, 6, and 11 are the ones that do not overlap.
Walk-through: port flapping. A desk phone and the PC plugged through it lose the network several times an hour. The switch log shows the port going down and up repeatedly. That is port flapping. The first check is physical: swap the patch cable, then try another switch port. If the flapping follows the cable, the cable was the cause. If it follows the port, the switch port is suspect. Changing the PC's IP settings would not help. The link itself is dropping.
Turn the tables into practice
Cover the last two columns of any table and say the first check out loud before you read it. If your answer is "replace the part," look for the cheaper test you skipped. Addressing clues and Wi-Fi bands are in more depth in the A+ networking guide.
When one of these areas keeps costing you points, target the A+ troubleshooting area you miss most with Passy practice. For a quick baseline first, use the free A+ practice questions.
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Official sources
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