220-1101 Mobile Devices Practice Question
A user reports that their smartphone's touchscreen is unresponsive in a small area near the bottom-left corner after dropping the device. The screen is not cracked, and the display still shows images correctly in that area. The technician has already performed a soft reset and verified that no screen protector is interfering. Which of the following is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates assume any physical damage after a drop must affect the display (LCD/OLED), but CompTIA tests the distinction between the digitizer (touch input) and the display panel (visual output) as separate layers in a smartphone screen assembly.
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
✓
A. The digitizer layer is damaged
The digitizer layer is the component responsible for detecting touch input. When a smartphone is dropped, the digitizer can sustain localized damage—such as a cracked or delaminated sensor grid—even if the display (LCD/OLED) remains intact and shows images correctly. The unresponsive area in the bottom-left corner, combined with normal image display, points directly to a damaged digitizer rather than 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.
- ✓
A. The digitizer layer is damaged
Why this is correct
The digitizer is the touch-sensitive layer of the display assembly, typically a transparent conductive grid that detects finger contact. A physical impact or sharp drop can fracture or delaminate the digitizer's localized conductive traces without affecting the LCD beneath it, because the two layers are mechanically separate. This precisely explains why the touchscreen is unresponsive only in a small area while the display continues to render normally, making it the correct diagnosis.
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B. The LCD panel is cracked internally
Why it's wrong here
An internally cracked LCD panel primarily disrupts the liquid crystal molecules and polarizer layers that control light transmission, producing unmistakable visual artifacts such as black splotches, color streaks, or complete dark regions. Because the user's display remains normal in the affected area and the only symptom is touch unresponsiveness, an internal LCD crack cannot be the cause. The LCD generates the image, while touch sensing belongs to a separate, overlying digitizer layer; a defect in one does not necessarily affect the other.
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C. The battery is swollen and pressing against the screen
Why it's wrong here
Incorrect. A swollen battery usually causes the screen to bulge or lift, and would likely affect a larger area or cause pressure spots visible on the display. It would not cause precise local touch failure without display distortion.
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D. The screen resolution settings are incorrect
Why it's wrong here
Screen resolution settings determine how many pixels are rendered and how content is scaled, which solely influences image output and has no bearing on the digitizer's hardware touch-sensing circuitry. A localized unresponsive region is caused by a physical break in the digitizer's sensing grid, not by software configuration; resolution errors would instead cause the entire touch axis to be offset or misaligned, producing wrong pointer positions everywhere, not a single dead zone. Therefore, incorrect resolution cannot account for a small, well-defined area where taps are ignored.
Go deeper
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Key term
Organic Light-emitting Diode
An Organic Light-emitting Diode (OLED) is a display technology that uses organic compounds to emit light when an electric current passes through them, enabling thin, flexible, and energy-efficient screens with high contrast.
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Written by Johnson Ajibi, MSc IT Security
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