CMT Device Troubleshooting & Repair 3 — Questions and Answers
Question 1: A phone charges slowly on all cables and chargers. A cotton swab reveals compacted lint in the charging port. What is the correct cleaning technique?
- Use a metal pin to dig out debris with force
- Carefully remove debris with a non-conductive plastic spudger or wooden toothpick (Correct answer)
- Blow compressed air directly into the port at full pressure
- Soak the port in isopropyl alcohol
Correct answer: Carefully remove debris with a non-conductive plastic spudger or wooden toothpick
A non-conductive tool allows safe debris removal without bending charging pins or causing short circuits.
Question 2: After a water damage repair, a device boots to the OS but has no cellular signal. All other functions work. What component is most suspect?
- NAND flash chip
- Cellular baseband module or its antenna connections (Correct answer)
- Touchscreen digitizer
- Front camera
Correct answer: Cellular baseband module or its antenna connections
Water damage often corrodes the baseband processor or antenna connector pads, eliminating cellular function while leaving Wi-Fi and other features intact.
Question 3: A technician is replacing the display on an iPhone and must heat the adhesive. What is the maximum recommended temperature to avoid damaging the battery?
- 25°C (77°F)
- 60°C (140°F) (Correct answer)
- 100°C (212°F)
- 120°C (248°F)
Correct answer: 60°C (140°F)
Heating adhesive above approximately 60°C risks thermal runaway in lithium batteries; 60°C is the safe upper limit for most repair heating.
Question 4: A customer reports their phone's GPS is inaccurate indoors but works perfectly outdoors. What is the most appropriate response?
- Replace the GPS chip
- Explain that GPS requires clear line of sight to satellites and works as intended (Correct answer)
- Perform a factory reset
- Re-flash the modem firmware
Correct answer: Explain that GPS requires clear line of sight to satellites and works as intended
GPS signals are significantly attenuated by building materials, making indoor GPS inherently inaccurate—this is normal device behavior, not a defect.
Question 5: You are repairing a device and notice the motherboard has a cracked solder joint on the power management IC. This repair requires:
- A standard soldering iron with rosin flux
- BGA rework station with hot air and stencils (Correct answer)
- Cold solder touch-up with no-clean flux pen
- Epoxy adhesive to stabilize the IC
Correct answer: BGA rework station with hot air and stencils
BGA (Ball Grid Array) ICs require hot-air rework stations to properly reflow all solder balls simultaneously without damaging surrounding components.
Question 6: A phone vibrates once when a charger is plugged in but won't charge. Battery voltage measures 3.2V. What does this indicate?
- The battery is beyond recovery at 0V and must be replaced
- The battery is in a deep discharge state requiring trickle charge or replacement (Correct answer)
- The charging port is completely broken
- The power button is stuck
Correct answer: The battery is in a deep discharge state requiring trickle charge or replacement
3.2V is below the typical 3.4V threshold for normal charging; the device recognizes the charger (vibrates) but the battery management system applies trickle charge or refuses full charge.
Question 7: Which tool is essential for measuring voltage and continuity when diagnosing a no-power condition on a logic board?
- Oscilloscope
- Digital multimeter (DMM) (Correct answer)
- Thermal camera
- Logic analyzer
Correct answer: Digital multimeter (DMM)
A DMM measures DC voltage at power rails and tests continuity of traces, making it the primary tool for no-power diagnosis.
CMT Device Troubleshooting & Repair 3
A phone charges slowly on all cables and chargers.
A cotton swab reveals compacted lint in the charging port.
What is the correct cleaning technique?