220-1101 Mobile Devices Practice Question
A user reports that their Android smartphone's touchscreen is unresponsive in a narrow vertical strip on the left side of the screen. The rest of the screen works normally. The user has removed the screen protector and cleaned the screen, but the issue persists. There is no visible damage, cracks, or discoloration. Which of the following is the MOST likely cause?
⚠ Common exam trap
CompTIA often tests the distinction between the digitizer (touch input) and the LCD (display output), and the trap here is that candidates confuse a display defect (like a stuck pixel or LCD failure) with a touch input problem.
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
✓
Digitizer failure
The touchscreen uses a digitizer layer to detect touch input. A narrow vertical strip of unresponsiveness, with no visible damage and after cleaning, indicates a localized failure of the digitizer's sensing grid. The LCD panel remains functional because display output is unaffected.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Software glitch requiring factory reset
Why it's wrong here
A software glitch typically disrupts the entire input processing pipeline, leading to global symptoms like ghost touches, erratic cursor jumps, or complete touchscreen unresponsiveness rather than a single, well-defined vertical dead zone. A vertical strip of inactivity indicates a physical defect in a specific row or column of the digitizer's sensing array, which a factory reset or firmware reflash cannot repair because no amount of software can restore continuity to a broken conductive trace or damaged sensor line.
- ✗
Stuck pixel
Why it's wrong here
A stuck pixel is a localized display panel defect where one subpixel (red, green, or blue) remains permanently lit or unlit due to a stuck transistor, resulting in a tiny dot on the screen. It is purely a visual artifact that does not interact with the capacitive touch sensing system, so it cannot cause a vertical region to lose touch input, and its appearance is a small colored dot, not a wide strip.
When this WOULD be correct
A user reports a single, unchanging bright or dark dot on the screen that does not respond to display changes. The touchscreen works fine, but the dot remains visible regardless of content. In that case, a stuck pixel is the likely cause.
- ✓
Digitizer failure
Why this is correct
The digitizer is the transparent capacitive sensing layer that sits above the LCD and converts touch into electrical signals. It is composed of a grid of X and Y electrodes, with each electrode responsible for detecting touches along its line; when a digitizer fails along a specific column trace, that entire vertical band becomes unresponsive while the rest of the screen continues to work. This matches the symptom of a 2-inch vertical strip that does not register input, making digitizer failure the correct diagnosis.
- ✗
LCD panel failure
Why it's wrong here
LCD panel failure affects the backlight and liquid crystal layers, producing visual abnormalities such as horizontal or vertical lines, color bleeding, dark patches, or a completely black screen. In contrast, the reported symptom is solely a loss of touch responsiveness in a vertical strip with no mention of any visual distortion, meaning the display layer is likely intact and the problem lies in the separate touch digitizer layer, not the LCD panel itself.
When this WOULD be correct
A question describing a cracked screen, black spots, or distorted colors that persist regardless of touch input would make LCD panel failure the correct answer. For example: 'The screen shows vertical lines and discoloration, but touch works fine.'
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓Digitizer failureCorrect answer▾
Why this is correct
The digitizer is the transparent capacitive sensing layer that sits above the LCD and converts touch into electrical signals. It is composed of a grid of X and Y electrodes, with each electrode responsible for detecting touches along its line; when a digitizer fails along a specific column trace, that entire vertical band becomes unresponsive while the rest of the screen continues to work. This matches the symptom of a 2-inch vertical strip that does not register input, making digitizer failure the correct diagnosis.
✗Stuck pixelWrong answer — click to see why▾
Why this is wrong here
A stuck pixel appears as a single, persistent dot of color on the display, not as a vertical strip of unresponsive touch input. The issue described involves touch sensitivity, not pixel display.
★ When this WOULD be the correct answer
A user reports a single, unchanging bright or dark dot on the screen that does not respond to display changes. The touchscreen works fine, but the dot remains visible regardless of content. In that case, a stuck pixel is the likely cause.
Why candidates choose this
Candidates may confuse a stuck pixel with a dead zone on the screen, or they may think any screen anomaly is a pixel issue, not understanding that the digitizer handles touch input separately from the LCD display.
✗LCD panel failureWrong answer — click to see why▾
Why this is wrong here
LCD panel failure typically causes display issues like discoloration, dimming, or image persistence across the entire screen, not a localized unresponsive strip. The touchscreen works via the digitizer, which is separate from the LCD panel.
★ When this WOULD be the correct answer
A question describing a cracked screen, black spots, or distorted colors that persist regardless of touch input would make LCD panel failure the correct answer. For example: 'The screen shows vertical lines and discoloration, but touch works fine.'
Why candidates choose this
Candidates may confuse the digitizer (touch layer) with the LCD (display layer), assuming any screen issue is due to the display panel itself, especially when the problem appears as a visible strip.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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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.