IT FundamentalsA+

Power Troubleshooting for CompTIA A+ 220-1101

Power issues prevent computers from starting or cause random shutdowns and instability. CompTIA A+ 220-1101 tests diagnosis of power supply failures, overheating, and electrical issues. Power troubleshooting requires systematic testing — from the outlet to the PSU to component connections — to avoid incorrectly blaming an expensive component when the PSU is the real culprit.

6 min

2 sections · 7 exam key points

1 practice questions

Power Failure Symptoms and Causes

System won't turn on at all: no fans, no LEDs, no beeps. Check: power outlet (test with another device), power cable (wall to PSU), PSU power switch on the back (I = on), front panel power button connections on the motherboard header. Bypass the power button: short the two PWR_SW header pins with a screwdriver — if the system starts, the power button or cable is faulty.

System powers on momentarily then shuts off: powers on for 1–2 seconds then dies. Causes: PSU cannot sustain required power (failing PSU or undersized), CPU cooler not seated properly triggering thermal protection, faulty motherboard, short circuit (something touching the board — check standoffs, cables). Test with PSU tester — check if voltages hold under minimal load.

Random shutdowns during use: powers off suddenly without warning. Causes: overheating (CPU, GPU), inadequate PSU power under load (GPU or CPU power spike triggers shutdown), failing PSU (voltage spikes), power surge from outlet. Check temperatures in HWiNFO or HWMonitor — CPU > 90°C or GPU > 95°C during shutdown indicates overheating. Check event viewer for critical power events before the shutdown.

Slow or sluggish performance with random errors: incorrect voltage from PSU rails can cause unstable operation without complete shutdown. Test PSU voltages with a multimeter on SATA or Molex connector: 12V rail should be 11.4–12.6V, 5V should be 4.75–5.25V. Out of spec = replace PSU.

Overheating Diagnosis and Prevention

Temperature monitoring: use HWiNFO64 or HWMonitor to log temperatures over time. CPUs vary but > 90–100°C indicates serious overheating. GPU typically safe up to 85–95°C depending on model. Causes: clogged heatsink/fan (dust), dried thermal paste, insufficient case airflow, case side panel off (counter-intuitive — directed airflow works better than open air), CPU cooler not making full contact.

Cooling fixes: use compressed air to blow dust from heatsink fins and fans (do outside or away from the system). Reapply thermal paste (clean old paste with 90%+ isopropyl alcohol, apply pea-sized amount of new paste to CPU center). Verify all case fans are running. Check for blocked vents. Ensure cables are managed to allow airflow. Add intake fans at front, exhaust fans at rear and top.

UPS (Uninterruptible Power Supply): battery backup for PCs — provides clean power during outages and protects against surges/sags. Gives the computer time to save and shut down gracefully during a power failure. Rated in VA (volt-amperes) and watts. Size UPS for the system's power draw × 1.5 for runtime margin. Replace UPS battery every 3–5 years.

Key exam facts — A+

PSU switch on back: I=on, O=off — most common overlooked 'no power' cause
Bypass power button: short PWR_SW header pins — tests if power button is faulty
Random shutdown under load: overheating or insufficient PSU wattage
PSU test: multimeter on 12V rail (11.4–12.6V), 5V rail (4.75–5.25V)
Overheating fix: clean dust from heatsink, reapply thermal paste, improve airflow
UPS: battery backup — graceful shutdown during power failure, surge protection
Event Viewer: check for critical events before unexpected shutdowns

Common exam traps

Running a computer without the side panel improves cooling

Desktop cases are designed for directed airflow — intake at the front, exhaust at the rear and top. Without the side panel, airflow patterns are disrupted and hot air can recirculate. Temperatures often INCREASE without the side panel in properly cabled systems. The only exception is cases with very poor airflow from clogged filters where open air temporarily helps — fix the root cause (clean filters, improve cable management) instead

Practice questions — Power Troubleshooting

These questions are representative of what you will see on A+ exams. The correct answer and explanation are shown immediately below each question.

Q1.A desktop computer shuts off unexpectedly after 20–30 minutes of use, especially when running demanding applications. When restarted immediately after shutdown, it powers on normally. What is the MOST likely cause?

A.Faulty RAM

B.Operating system corruption

C.Overheating — thermal protection shutting down the CPU or GPU

D.Failing hard drive

Explanation: The pattern — shuts down after sustained load (heating up), then restarts fine immediately (components not yet critically hot) — is the classic thermal throttle/shutdown signature. The CPU or GPU exceeds its maximum safe temperature under sustained load and the thermal protection circuit shuts down the system to prevent damage. Monitor temperatures with HWiNFO during a stress test. Fix: clean dust from heatsink/fans, reapply thermal paste, improve case airflow. RAM failure and storage issues cause different symptoms (crashes, errors, data corruption) — not time-dependent thermal shutdowns.

Frequently asked questions — Power Troubleshooting

What is the difference between a surge protector and a UPS?

Surge protector: clamps voltage spikes from the power outlet — protects equipment from surges (lightning strikes, electrical switching). No battery backup. When power goes out, connected equipment immediately loses power and shuts off without warning. UPS (Uninterruptible Power Supply): includes a surge protector PLUS a battery — during a power outage, the battery instantly powers connected equipment for several minutes, allowing graceful shutdown or waiting for power restoration. For servers and critical workstations, a UPS is essential. For general desktops, at minimum a surge protector. Using neither leaves equipment vulnerable to power events.

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