220-1101 Mobile Devices Practice Question
A technician replaces a smartphone's fused screen assembly (LCD + digitizer + glass). After reassembly, the phone powers on and the display shows correctly, but the touchscreen is completely unresponsive. Which of the following is the most likely cause?
⚠ Common exam trap
CompTIA often tests the misconception that a fused assembly means all functions share one cable, leading candidates to overlook the separate digitizer connection.
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
✓
The digitizer cable is not connected
The fused screen assembly includes the LCD, digitizer, and glass. The digitizer is responsible for touch input, and it connects to the motherboard via a separate ribbon cable. If the display works but the touchscreen is unresponsive, the digitizer cable is likely not connected or is loose, as the LCD cable only handles video output.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The LCD cable is loose
Why it's wrong here
A loose LCD cable would disrupt the high-speed display signal carrying pixel data and timing synchronization. This manifests as a blank screen, horizontal or vertical lines, color banding, or flickering—not as an isolated loss of touch. In a fused assembly, the LCD and digitizer have entirely separate cables even though the glass and LCD are bonded together; a loose LCD cable leaves the digitizer's connection untouched. Because the display is crisp and stable, the LCD cable must be seated securely, so this cannot explain the unresponsive touch.
When this WOULD be correct
In a scenario where after reassembly the screen is completely black or shows no image (but the phone powers on, e.g., vibrates or makes sounds), a loose LCD cable would be the most likely cause.
- ✓
The digitizer cable is not connected
Why this is correct
The digitizer cable is a dedicated flex circuit that carries capacitive touch signals from the screen's sensor layer to the touch controller IC. In a fused display assembly, the LCD and digitizer are bonded together but maintain separate electrical connections; the LCD can receive image data over its own cable while the digitizer's cable remains unseated. Without a completed digitizer connection, the touch controller receives no input from the sensor grid, so the screen shows a perfect image but ignores all touches. This is a classic symptom when a technician replaces a fused assembly and forgets to reattach the separate touch cable.
- ✗
The battery is not fully seated
Why it's wrong here
An improperly seated battery would cause a catastrophic power delivery problem, not a selective peripheral failure. If the battery connector is loose, the phone might not power on at all, or it could suddenly reboot or shut down when current draw increases—especially during a touch event that triggers display backlight changes. A fully working display with normal brightness and no shutdown indicates that the main power rails are stable and within tolerance. The digitizer requires only a low-voltage supply from the same power management IC, so if the phone stays on and displays correctly, battery seating is irrelevant to touch failure.
When this WOULD be correct
A technician replaces a smartphone battery, and after reassembly, the phone fails to power on or powers off intermittently. The most likely cause is the battery connector not being fully seated.
- ✗
The new screen assembly is incompatible with the phone's OS
Why it's wrong here
Screen assembly incompatibility with the phone's OS would not selectively disable touch while leaving the display intact. The OS communicates with the display controller through a standardized interface (such as MIPI DSI), and a mismatched panel typically fails to initialize, producing no backlight, garbled lines, or incorrect color/resolution. Touch input is handled by a separate I2C or USB interface with its own driver; an incompatible part would almost certainly cause both subsystems to fail or show immediate startup errors. Since the display renders correctly, the panel's internal driver is recognized and functioning—eliminating OS-level incompatibility as the cause.
When this WOULD be correct
A technician installs a third-party screen assembly on a smartphone, and the touchscreen registers touches in the wrong locations or not at all, while the display works. The question specifies that the phone's OS version was recently updated and the replacement screen is from an untested manufacturer. In that case, OS-level driver incompatibility could be the 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.
✓The digitizer cable is not connectedCorrect answer▾
Why this is correct
The digitizer cable is a dedicated flex circuit that carries capacitive touch signals from the screen's sensor layer to the touch controller IC. In a fused display assembly, the LCD and digitizer are bonded together but maintain separate electrical connections; the LCD can receive image data over its own cable while the digitizer's cable remains unseated. Without a completed digitizer connection, the touch controller receives no input from the sensor grid, so the screen shows a perfect image but ignores all touches. This is a classic symptom when a technician replaces a fused assembly and forgets to reattach the separate touch cable.
✗The LCD cable is looseWrong answer — click to see why▾
Why this is wrong here
The LCD cable only handles video signal; a loose LCD cable would cause display issues (no image, distorted image, or blank screen), not a completely unresponsive touchscreen while the display works perfectly.
★ When this WOULD be the correct answer
In a scenario where after reassembly the screen is completely black or shows no image (but the phone powers on, e.g., vibrates or makes sounds), a loose LCD cable would be the most likely cause.
Why candidates choose this
Candidates may confuse the LCD cable with the digitizer cable, assuming both are part of the same assembly and that a loose cable would affect both display and touch, or they may not distinguish between the two separate connections.
✗The battery is not fully seatedWrong answer — click to see why▾
Why this is wrong here
The battery not being fully seated would prevent the phone from powering on or cause unexpected shutdowns, but it would not cause a fully functional display with a completely unresponsive touchscreen.
★ When this WOULD be the correct answer
A technician replaces a smartphone battery, and after reassembly, the phone fails to power on or powers off intermittently. The most likely cause is the battery connector not being fully seated.
Why candidates choose this
Candidates may think that any loose connection (including battery) could cause touchscreen issues, or they confuse the battery's role in powering the digitizer with the digitizer's own connection.
✗The new screen assembly is incompatible with the phone's OSWrong answer — click to see why▾
Why this is wrong here
Incompatibility with the OS would typically cause display issues (e.g., no image, wrong colors) or erratic touch behavior, not a completely unresponsive touchscreen while the display works perfectly. The digitizer is a separate hardware component; OS compatibility is rarely the cause of total touch failure after a replacement.
★ When this WOULD be the correct answer
A technician installs a third-party screen assembly on a smartphone, and the touchscreen registers touches in the wrong locations or not at all, while the display works. The question specifies that the phone's OS version was recently updated and the replacement screen is from an untested manufacturer. In that case, OS-level driver incompatibility could be the cause.
Why candidates choose this
Candidates may think that any hardware issue after a replacement could be due to incompatibility, especially if they have experienced cases where aftermarket parts don't work with certain OS updates. They overlook that a completely dead touchscreen with a working display points to a disconnected digitizer cable, not software incompatibility.
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.