Subject: Computer Hardware and GSM Repairs 1 | Level: Senior Secondary (WASSCE)
This module forms the core of the WAEC Practical Exam, focusing heavily on step-by-step diagnostic procedures and fault-finding logic.
Key Topics:
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What is the primary purpose of performing a 'Visual Inspection' as the first step in mobile phone troubleshooting?
To physically examine the motherboard for obvious damage like burnt components, liquid residue, or broken connectors.
Visual inspection is the basic troubleshooting method of looking closely at the hardware before applying power or tools, searching for physical clues like water damage or burnt chips.
In mobile hardware troubleshooting, what is the main difference between 'cold testing' and 'hot testing'?
Cold testing is performed with the phone powered off using a multimeter (continuity/resistance), while hot testing measures live voltages with power applied.
Cold testing (unpowered) is typically used for checking continuity, diode mode values, and shorts to ground. Hot testing (powered) checks if the correct working voltages are reaching various components.
During a hot test on a completely dead logic board, which of the following voltage lines must usually be verified first to ensure power is reaching the Power Management IC (PMIC)?
The VPH_PWR (or VBAT/VSYS) main power line
The VBAT (Battery Voltage) or VPH_PWR (System Power) line distributes the primary voltage from the battery/charge IC to the PMIC. Without this primary voltage, the PMIC cannot generate secondary voltages.
A customer complains that during a phone call, they can hear the other person perfectly, but the other person cannot hear them at all. Which hardware component is most likely faulty?
The microphone (mic)
The microphone is the input device responsible for capturing the user's voice. If it fails, the caller's voice is not transmitted, though the earpiece (receiving audio) works fine.
If a smartphone produces sound clearly when put on 'speakerphone' but produces no sound during normal private calls when held to the ear, which specific component is faulty?
The earpiece speaker (receiver)
Smartphones use two different speakers. The bottom loudspeaker is used for media and speakerphone, while the top earpiece (receiver) is dedicated to private calls.
When tracing a complex short circuit on a mobile motherboard, a technician decides to use the 'Rosin Smoke Method' (vaporized flux). How does this method help pinpoint the shorted component?
A layer of white rosin frost is deposited on the board; when power is injected, the shorted component heats up and melts the frost rapidly.
The Rosin Smoke Method relies on thermal dissipation. The technician coats the board in vaporized rosin (white frost). Injecting voltage causes the shorted part to heat up, immediately melting the white rosin on that specific component.
What is the recommended professional treatment for a motherboard suffering from severe oxidation due to water/liquid damage?
Removing the EMI shields and cleaning the motherboard in an ultrasonic cleaner using a specialized PCB cleaning solution or isopropyl alcohol.
Rice does not clean oxidation. Ultrasonic cleaning reaches underneath microscopic BGA chips, using cavitation in a solvent (like isopropyl alcohol) to strip away conductive mineral deposits left by water.
In logic board diagnostics, what defines a 'secondary short'?
A short circuit occurring on one of the regulated output voltage lines (buck/ldo) originating from the Power Management IC.
A primary short is directly on the main voltage rail (VPH_PWR / VBAT). A secondary short is downstream of the PMIC on lines like 1.8v or 1.2v logic rails, meaning the phone draws no abnormal current until the power button is pressed to activate the PMIC.
What is the simplest and very first hardware diagnostic step a technician should perform when repairing a completely dead (no power) phone?
Test the battery voltage with a multimeter to ensure it holds sufficient charge (approx. 3.7V - 4.2V) to boot the device.
A heavily depleted battery (under 3.6V) will prevent a phone from booting or even showing charging signs. Testing/boosting the battery is the necessary first step before invasive logic board repair.
A phone's screen displays a perfect image with no bleeding or dead pixels, but it entirely fails to respond to finger inputs. Which specific physical layer of the screen assembly has failed?
The digitizer (touch glass/panel)
Screen assemblies consist of a display layer (LCD/OLED) to show the image, and a digitizer glass layer layered over it to register touch inputs.
