220-1101 Mobile Devices Practice Question
A technician is repairing a smartphone with a cracked screen. After replacing the screen assembly, the touch screen is completely unresponsive, although the display shows properly. The technician has verified that the digitizer flex cable is firmly seated in the connector on the motherboard. Which of the following should the technician check NEXT?
⚠ Common exam trap
CompTIA often tests the misconception that a firmly seated flex cable guarantees full digitizer functionality, when in fact a missing grounding screw is a separate, critical requirement that candidates overlook.
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
✓
Check that the grounding screw for the digitizer is installed and tight
Many smartphone digitizer assemblies require a dedicated grounding screw to complete the circuit for capacitive touch sensing. Without this ground, the digitizer may receive power and data via the flex cable but cannot establish a stable reference voltage, causing the touch screen to be completely unresponsive even though the display works. The technician has already verified the flex cable connection, so checking the grounding screw is the logical next step.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Check that the LCD cable is properly connected
Why it's wrong here
This is incorrect because the LCD cable carries the display signal, and the display is functioning normally. A loose or disconnected LCD cable would manifest as a black screen, distorted image, or backlight issues, not a lack of touch response. The touch screen uses a separate digitizer cable, so inspecting the LCD cable won't address the touch failure.
- ✗
Check the digitizer cable for damage or improper orientation
Why it's wrong here
You've already confirmed the digitizer cable is firmly seated, but subtle damage or incorrect orientation could theoretically cause touch issues. However, after a screen replacement, a missing grounding screw is a far more common culprit. Even with a good cable, the capacitive touch screen needs a chassis ground to function, so if the cable checks out, the ground connection should be verified next.
- ✓
Check that the grounding screw for the digitizer is installed and tight
Why this is correct
The digitizer relies on a ground screw that connects the touch sensor layer to the phone's metal frame, establishing a reference potential for the capacitive controller. Without this screw installed and tightened, the controller cannot measure the capacitance difference from your finger, so the display may appear normal while touches go unregistered. This is a frequent oversight when replacing a screen, as the screw is often located near a bracket or along the edge of the frame. Confirm it's present and torqued to the manufacturer's spec.
- ✗
Replace the battery
Why it's wrong here
The battery is not implicated here because the device is powered on and the display is working, which proves the power rails are functional. A failing battery typically causes sudden shutdowns, random reboots, or charging problems, not the loss of touch input. The digitizer is powered from the same system supply that's already operating, so replacing the battery would have no effect on the touchscreen.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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