220-1101 Mobile Devices Practice Question
A user reports that their smartphone will not power on. When they plug it into a charger, the LED indicator flashes red but the screen remains black. The phone was working normally earlier in the day and was not dropped or exposed to water. Which of the following is the MOST likely cause?
⚠ Common exam trap
Many exam-takers assume a black screen must be a display or screen issue, but the red LED indicator is a critical clue that the charging circuit is active and the problem is likely power-related, not display-related.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Faulty battery
The LED indicator flashing red when the charger is connected, combined with a black screen and no prior physical damage or water exposure, strongly points to a battery that has entered a deep discharge state or has failed. In this scenario, the battery cannot hold enough charge to power the phone's boot sequence, but the charging circuit can still detect the charger and attempt to charge, causing the red LED. A faulty battery is the most common cause of a device that was working normally and then suddenly will not power on, especially when the screen remains black but the LED responds.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Faulty battery
Why this is correct
A deeply discharged or defective lithium-ion battery is the most common cause of this symptom. When the battery voltage drops below the PMIC's power-on threshold, the charging circuit enters trickle-charge mode, drawing only a few milliamps to safely raise the cell voltage; the steady red LED indicates the charge controller detects the battery and is attempting this recovery charge, but the phone cannot boot until the battery reaches a minimum voltage. If the battery has an internal short or its protection circuit has tripped, it may never accept a charge, leaving the phone unresponsive while plugged in.
- ✗
Damaged screen
Why it's wrong here
A damaged screen affects only the display output; it has no connection to the power-on sequence or charging circuit. If the battery and logic board are sound, the phone will still power on normally when plugged in—the charging LED will respond, the device may vibrate or play a startup sound, and the system will boot even if the panel stays black. The presence of a red LED with no other signs of activity points to a power delivery problem, not a failed display, so a cracked or shattered screen would not produce this symptom.
- ✗
Failed CPU
Why it's wrong here
A failed application processor (CPU) typically causes a complete loss of system power because the CPU is responsible for telling the PMIC to enable the main power rails after boot. In that case, you would see no LED at all—or, if the CPU partially works, a boot loop that never progresses—because the charging LED is driven by the PMIC independently of the CPU. Here, the steady red LED proves the PMIC and charging path are alive, which strongly argues against a dead CPU as the root cause.
- ✗
Corrupted firmware
Why it's wrong here
Corrupted firmware (e.g., a failed OTA update or interrupted bootloader write) leaves the boot ROM and PMIC fully functional, so the phone will attempt to run the bootloader and then either hang on the logo or restart in a loop. A steady red LED while charging, with no logo, no vibration, and no boot attempts, indicates the battery is too depleted for the PMIC to even authorize a full-power boot. Therefore, firmware corruption cannot explain a purely red charge indicator with zero other system activity.
Go deeper
Related to this question
About these practice questions
Courseiva writes every 220-1101 question from scratch — 896 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.