Domain 1 of 5 · Chapter 4 of 4

Mobile Troubleshooting

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Included in this chapter:

  • The mobile troubleshooting ladder
  • Power and thermal: charging, drain, swelling, and heat
  • Display and touch: dim, flicker, cracked, dead touch
  • Radios: Wi-Fi, cellular, and Bluetooth
  • Physically damaged ports
  • How the exam frames mobile troubleshooting

Battery and thermal symptoms: usual cause and first action

AspectWon't chargeDrains fastSwollen packOverheating
Usual causeCable, port, or worn batteryBackground apps or an aging cellThe lithium cell has failedHeavy load or blocked cooling
First actionSwap in a known-good cable and chargerCheck the battery-usage list, lower brightnessStop and remove from serviceReduce load, clear vents, remove the case
Safety riskLowLowHigh: fire and ruptureModerate: heat can worsen a weak cell
Escalates toClean the port, then replace the batteryReplace the aging batteryControlled battery replacementBattery or cooling-path service

Decision tree

Battery swollen or case bulging? Yes No Stop: remove from service swollen cell, fire hazard Will not charge or power on? Yes No Cable, then port, then battery Running hot or shutting down? Yes No Reduce load, clear vents remove a heat-trapping case No Wi-Fi, cellular, or Bluetooth? Yes No Config first: toggle, range then forget or re-pair Display or touch wrong? Yes No Isolate the display layer Climb the ladder restart, update, re-seat, then open
Cheat sheet

Cheat sheet

  • Try the cheapest fix before you open a mobile device
  • Diagnose a no-charge fault as cable, then port, then battery
  • A phone that won't charge often has a lint-packed port
  • A swollen battery is a fire hazard: remove it from service
  • Overheating first throttles, then shuts down to protect the device
  • Rapid battery drain is usually a background app, not a dead cell
  • Prove a black screen with an external display
  • A dim screen is a brightness setting until proven otherwise
  • A faint image under a flashlight means the backlight failed
  • Screen flicker that changes as you flex the lid is a cable
  • Image but no touch is a digitizer fault, not a panel fault
  • Ghost touches point at the digitizer, a cheap charger, or a protector
  • A screen that won't rotate is the auto-rotate setting, not the display
  • Cracked glass and dead touch are separate faults
  • Check airplane mode before troubleshooting any dead radio
  • Forget and rejoin a Wi-Fi network to clear a stale profile
  • Bluetooth pairing needs the accessory discoverable and in range
  • A cable that charges only at an angle is a worn port
  • Reseat the SIM when a phone loses cellular but has coverage
  • Weak signal right after a screen repair is an unseated antenna lead
  • Use ESD protection whenever you open a mobile device
  • Organize screws by location and never overtighten on reassembly
  • Screen lines, dead pixels, and stuck pixels that survive a restart are panel hardware faults
  • A phone that charges over USB but shows no storage is in charging-only mode or on a power-only cable

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References

  1. CompTIA A+ Core 1 (220-1201) certification and exam objectives