Core 1 troubleshooting is 28% of 220-1201, the largest domain on the exam. The objective map expects you to diagnose motherboard, memory, processor, power, storage, display, mobile, network, and printer problems from symptoms and evidence.
CompTIA also describes its troubleshooting methodology as useful job practice, but the methodology itself is not a formal 220-1201 objective. Use the process to think clearly rather than trying to memorize it as another numbered exam list.
Fast rule: A symptom narrows the subsystem. Evidence narrows the cause. Replace or reconfigure only after the evidence points there.
1. Troubleshooting decision map
| Symptom | Think first | Useful evidence |
|---|---|---|
| No power | Power source, PSU, connectors, board | Outlet, adapter/PSU state, standby lights, power connectors |
| Powers on but does not complete startup | POST, RAM, CPU, board, firmware | Beep/LED codes, reseating result, firmware settings |
| Drive missing or slow | Storage connection, health, interface, RAID | Firmware detection, SMART/health, cable, array state |
| No or distorted image | Cable, input, display, GPU, resolution | Known-good cable/display, selected input, display settings |
| Internet complaint | Scope first | Wi-Fi association, IP settings, gateway, DNS, another client |
| Bad printed output | Printer process or consumable | Pattern of defect, supplies, maintenance state, test page |
2. Separate power, motherboard, CPU, and memory clues
A system that is completely dead is a different problem from one that powers on but fails Power-On Self-Test (POST).
No power
Check the power source, cable or adapter, power supply, required motherboard and CPU power connectors, and any obvious physical damage before blaming storage or the operating system.
A power supply can have enough capacity on paper and still be faulty. A newly built system may also fail because a connector was missed, the front-panel power lead is wrong, or the board is shorted by installation hardware.
Power but no successful POST
Think about:
- Poorly seated or incompatible RAM
- Failed memory module
- CPU installation or cooling problem
- Motherboard fault
- Firmware configuration
- Expansion card or peripheral preventing startup
POST beep or diagnostic-light patterns are useful because they point toward the subsystem before the operating system loads.
Random restart or shutdown
Heat and unstable power are stronger starting points than reinstalling Windows. Check fans, heatsinks, dust, airflow, temperature, PSU behavior, and whether the problem appears under load.
Memory problems can also create intermittent crashes or failure to boot. Reseating or testing modules one at a time can help isolate a bad module or slot.
3. Use detection, health, and array state for storage problems
Ask three questions:
- Does the firmware or operating system see the drive?
- Is the drive healthy enough to trust?
- If RAID is involved, what is the array state?
A drive that is not detected suggests a connection, power, slot, interface, firmware, or failed-device problem before it suggests a filesystem problem.
Performance degradation, repeated read/write errors, health warnings, or unusual mechanical noise can indicate a failing drive. Protect data before aggressive testing when failure is plausible.
For RAID, distinguish a failed member from the entire array. A degraded array may continue operating with reduced protection. Replacing the correct failed drive and allowing the array to rebuild is different from recreating or formatting the array.
4. Troubleshoot the signal path before replacing the display
For no image, wrong image, or projector problems, work through the path:
- Is the device powered?
- Is the correct input selected?
- Is the cable connected and appropriate?
- Does a known-good cable change the symptom?
- Does another display work?
- Is the system sending a supported resolution and refresh rate?
- Is the graphics adapter or driver functioning?
- On a laptop, is the internal display or external-output mode selected correctly?
A dim laptop display, flickering image, distorted colors, stuck pixels, or image that appears only at certain lid angles can point toward different display, backlight, cable, or panel problems.
Projector complaints can also involve focus, lamp/light-source life, keystone settings, input selection, or the source device rather than the projector itself.
5. Treat mobile symptoms as power, physical, connectivity, or software evidence
A swollen battery is a safety issue. Stop normal use and charging, then follow the organization's battery-handling procedure.
Other useful distinctions:
- Will not charge: cable, charger, port, battery, debris, or charging circuitry
- Battery drains quickly: battery health, background activity, radio use, display, application behavior
- Overheating: workload, battery, environment, charging, blocked cooling, failing hardware
- Cracked screen but normal image: physical glass/digitizer issue may differ from display-panel failure
- No Wi-Fi: radio state, saved network, authentication, range, access point, or device hardware
- Poor performance: storage pressure, background apps, malware, battery/thermal behavior, update state
Do not replace hardware before checking a simple state such as airplane mode, disabled Wi-Fi, or a bad charger.
6. Start network troubleshooting by finding the scope
Ask whether the problem affects:
- One application
- One device
- One wireless area
- One local network
- Every device using the same internet connection
That scope eliminates many bad answers.
Useful clues include:
- No Wi-Fi association: radio, SSID, credentials, range, interference
- Self-assigned 169.254.x.x address: Dynamic Host Configuration Protocol (DHCP) or local connectivity problem
- Valid IP but no remote network access: default gateway, routing, upstream connection, firewall
- IP addresses work but names fail: Domain Name System (DNS)
- Slow or unstable Wi-Fi: signal strength, interference, congestion, channel choice, distance
- Only one service fails: service, port, local firewall, server, application configuration
Changing DNS will not repair a device that never joined the wireless network. Replacing the router is excessive when only one laptop has a bad saved password.
7. Match printer symptoms to the print process
First separate communication from output quality.
If the printer never receives the job, check the queue, selected printer, connectivity, address/port, driver, permissions, and device state.
If the printer receives the job but output is poor, look at the technology and defect pattern.
Common clues:
- Paper jam or misfeed: paper path, rollers, tray, paper condition
- Faded laser output: toner, drum/transfer/fusing process, maintenance state
- Repeating laser defects: rotating component in the imaging path
- Smudged or unfused laser output: fusing problem
- Inkjet streaks/missing colors: ink level, clogged printhead/nozzles, alignment
- Thermal output problems: thermal paper orientation/quality, printhead
- Impact printer faint or uneven: ribbon, printhead, paper-feed path
Use a printer test or configuration page when it can separate a printer-engine problem from the computer or application.
8. Collect evidence before replacing components
Good troubleshooting changes one meaningful variable at a time.
Useful evidence includes:
- Diagnostic LEDs, POST codes, or beep patterns
- Firmware device detection
- Drive health and RAID status
- Temperatures and fan operation
- Known-good cable, charger, display, port, or peripheral
- IP configuration and DNS settings
- Signal strength and whether other wireless clients work
- Printer self-test pages and supply/maintenance state
If a known-good cable fixes the problem, that evidence is stronger than a guess that the motherboard must be bad.
9. Scenario comparisons
PC is completely dead after a hardware upgrade
Check power delivery and connectors before storage or operating-system settings. The symptom occurs before those layers matter.
System restarts during gaming but is stable at idle
Load-related heat or power deserves attention. Check temperatures, cooling, and power stability before reinstalling applications.
Laptop gets a 169.254 address while nearby devices work
The laptop did not receive normal DHCP configuration. Check its local link, Wi-Fi association, adapter state, and DHCP path before changing DNS.
User can ping an IP address but not open the same server by name
DNS is the stronger clue. Basic IP reachability already works.
Laser printer text rubs off the page
Think about the fusing stage rather than the network queue. The printer has already produced the page.
Projector works with another laptop
The evidence moves attention back toward the original laptop's output mode, cable/adapter, resolution, or graphics configuration.
10. Common exam traps
- Replacing a component before checking power, cable, seating, or configuration.
- Reinstalling an operating system for a problem that occurs before POST.
- Treating every slow computer as a storage failure.
- Treating every internet complaint as a router failure.
- Changing DNS when the client has no valid IP configuration.
- Blaming Wi-Fi signal strength when only one saved credential is wrong.
- Replacing a printer because one workstation has the wrong queue or driver.
- Using an output-quality fix for a job that never reached the printer.
- Ignoring safety when a battery is swollen or hardware is overheating.
- Changing several settings at once and losing the evidence that identifies the cause.
11. Rapid review grid
| Clue | Think first |
|---|---|
| No power at all | Power source, PSU/adapter, required connectors |
| Power but no POST | RAM, board, CPU, firmware, POST evidence |
| Drive not detected | Power, connection, slot/interface, failed drive |
| 169.254.x.x | DHCP/local network path |
| IP works, names fail | DNS |
| Wi-Fi slow in one area | Signal, interference, congestion |
| Print job never arrives | Queue, connectivity, driver, selected printer |
| Print arrives with defects | Printer technology and imaging/feed process |