220-1101 Mobile Devices Practice Question
A user reports that the touchscreen on their smartphone is unresponsive in the bottom-left corner but works everywhere else. Which component is most likely failing?
⚠ Common exam trap
Many exam-takers confuse a display issue (dead pixels or backlight failure) with a touch input issue, not realizing that the digitizer and LCD are separate components that can fail independently.
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's digitizer is the layer responsible for detecting touch input. When a specific region of the screen becomes unresponsive while the display itself remains functional, it indicates a localized failure of the digitizer's grid or controller, not the LCD panel.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Dead pixels
Why it's wrong here
Dead pixels are permanent cosmetic defects in the display panel itself, where individual sub-pixels fail to illuminate correctly, creating tiny dark or colored dots. They do not affect the capacitive touch layer (digitizer) that detects your finger, so unresponsive zones cannot result from dead pixels. Touch sensitivity is entirely independent of pixel function, and a localized loss of response indicates a physical problem with the digitizer, not the LCD or OLED image output.
- ✓
Digitizer failure
Why this is correct
The digitizer is the transparent capacitive sensor layer that overlays the display and registers touch input. When a specific area of the screen becomes unresponsive while the rest still works, it is a classic sign of partial digitizer failure—often caused by cracks, impact damage, or a broken trace in that region's sensing grid. Unlike software glitches, this failure is localized and persistent, and it requires hardware repair, typically replacing the entire screen assembly.
- ✗
LCD backlight issue
Why it's wrong here
The LCD backlight provides illumination behind the display panel; when it fails, the screen may appear dark, dim, or blotchy. However, the backlight has no role in touch detection—the digitizer operates using capacitive sensing, which measures the electrical charge of your finger. Even with a completely failed backlight, the touchscreen would still register touches if the digitizer and controller are intact, so a black or unevenly lit screen cannot explain a localized unresponsive area.
When this WOULD be correct
A user reports that the screen is very dim or completely black, but the device still powers on and makes sounds. In that scenario, the LCD backlight or inverter would be the likely failing component.
- ✗
Pending OS update
Why it's wrong here
A pending OS update might cause temporary or system-wide touch issues due to software bugs, but it would rarely affect only one isolated region of the screen. Software problems typically result in erratic, laggy, or fully unresponsive behavior across the entire digitizer, not a hard cutoff at a specific physical boundary. Since the described symptom is a single localized dead zone, it points to a hardware defect in the digitizer, not a software update waiting to be applied or a driver conflict.
When this WOULD be correct
A user reports that the smartphone occasionally freezes and apps crash after a recent update notification appeared. Which is the most likely cause?
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 sensor layer that overlays the display and registers touch input. When a specific area of the screen becomes unresponsive while the rest still works, it is a classic sign of partial digitizer failure—often caused by cracks, impact damage, or a broken trace in that region's sensing grid. Unlike software glitches, this failure is localized and persistent, and it requires hardware repair, typically replacing the entire screen assembly.
✗LCD backlight issueWrong answer — click to see why▾
Why this is wrong here
The LCD backlight issue affects overall screen brightness or uniformity, not touch input. Since the touchscreen is unresponsive only in one area, the problem is with touch detection, not display illumination.
★ When this WOULD be the correct answer
A user reports that the screen is very dim or completely black, but the device still powers on and makes sounds. In that scenario, the LCD backlight or inverter would be the likely failing component.
Why candidates choose this
Candidates may confuse display-related issues (like backlight) with touch-related issues (digitizer), assuming any screen problem involves the LCD or backlight.
✗Pending OS updateWrong answer — click to see why▾
Why this is wrong here
A pending OS update does not cause localized touchscreen unresponsiveness; it typically affects system-wide performance or introduces bugs that are not limited to a specific screen region.
★ When this WOULD be the correct answer
A user reports that the smartphone occasionally freezes and apps crash after a recent update notification appeared. Which is the most likely cause?
Why candidates choose this
Candidates may think that software issues like a pending update can cause touch input problems, but they overlook that such issues are usually global, not localized to one corner.
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.