CMT Device Troubleshooting & Repair 2 — Questions and Answers
Question 1: A smartphone powers on but the touchscreen is completely unresponsive after a drop. The display shows the home screen correctly. What is the most likely cause?
- Failed GPU
- Digitizer layer damage or disconnected digitizer cable (Correct answer)
- Corrupted OS kernel
- Dead battery cells
Correct answer: Digitizer layer damage or disconnected digitizer cable
A drop can crack or disconnect the digitizer (touch sensor layer) while leaving the display itself functional.
Question 2: After replacing a phone battery, the device reports 0% charge and shuts down immediately even though the new battery is fully charged. What should you check first?
- Re-flash the bootloader
- Inspect the battery connector pins and re-seat the connector (Correct answer)
- Replace the charging port
- Perform a factory reset
Correct answer: Inspect the battery connector pins and re-seat the connector
A loose or misaligned battery connector prevents proper voltage reading and causes the device to shut down as if the battery is dead.
Question 3: A tablet's front camera works but the rear camera app crashes immediately upon launch. Other apps function normally. What is the most likely cause?
- Defective rear camera module or its flex cable (Correct answer)
- Cracked screen digitizer
- Corrupted display driver
- Failed USB controller IC
Correct answer: Defective rear camera module or its flex cable
A hardware failure in the rear camera module or a disconnected/damaged flex cable causes the camera app to crash when trying to access that specific sensor.
Question 4: A customer's phone overheats during light tasks and the battery drains in under 2 hours. Battery health shows 41%. What repair is indicated?
- Replace the logic board
- Replace the thermal paste
- Replace the battery (Correct answer)
- Clean the charging port
Correct answer: Replace the battery
A battery at 41% health has severely degraded capacity and internal resistance, causing it to generate excessive heat under even minimal load.
Question 5: During a screen replacement, you accidentally leave a fingerprint on the OLED panel's inner surface. What is the correct procedure?
- Wipe with an isopropyl alcohol-dampened microfiber cloth (Correct answer)
- Use compressed air only
- Proceed with reassembly since it won't affect display
- Apply screen protector to mask it
Correct answer: Wipe with an isopropyl alcohol-dampened microfiber cloth
IPA on a microfiber cloth safely removes oils from the inner OLED surface without damaging the panel coating.
Question 6: A phone's speaker produces distorted audio at all volume levels but earpiece audio is clear. Which component should you replace?
- Earpiece speaker
- Loudspeaker/bottom speaker assembly (Correct answer)
- Audio codec IC
- Microphone module
Correct answer: Loudspeaker/bottom speaker assembly
Distortion across all volumes while earpiece remains clear isolates the fault to the loudspeaker unit itself.
Question 7: A device shows 'No SIM Card Detected' after a repair. The SIM card and tray are correctly installed. What should you check?
- Re-flash carrier firmware
- Inspect and re-seat the SIM card reader connector on the motherboard (Correct answer)
- Replace the battery
- Factory reset the device
Correct answer: Inspect and re-seat the SIM card reader connector on the motherboard
Repairs often disturb the SIM reader connector; a loose connector causes the device to fail to detect a properly inserted SIM.
CMT Device Troubleshooting & Repair 2
A smartphone powers on but the touchscreen is completely unresponsive after a drop.
The display shows the home screen correctly.
What is the most likely cause?