Repair Case Study – SS3 Computer Hardware & GSM Repair Lesson Note (First Term)

A repair case study is a real-life example of a faulty phone or computer, followed from the customer’s complaint to the fix. The technician treats the complaint as a symptom, then finds the cause by following four steps: observation, testing, diagnosis and repair. This lesson applies that path to three cases.

Subject: Computer Hardware and GSM Repair
Class: SS3
Topic: Real-life repair scenarios and troubleshooting logic

Behavioural objectives

By the end of the lesson, students should be able to:

• state the professional repair path: Observation → Testing → Diagnosis → Repair;
• describe the steps for repairing a water-damaged phone;
• identify overheating as the cause of a laptop that shuts down suddenly, and list the repair steps;
• explain how a USB current analyser helps to diagnose a phone that “charges” but stays at 1%;
• state the four golden rules of a professional workshop.

How does a technician work like a detective?

Repairing a phone or a computer needs more than a screwdriver. You must work like a detective. When a customer walks into your shop, they bring a “symptom” (for example, “It won’t charge”). Your job is to find the “cause.”

The professional follows this path: Observation → Testing → Diagnosis → Repair.

Case study 1: the “dead” phone (water damage)

The scenario

A customer dropped their Android phone in a bowl of water yesterday. They dried it with a hair dryer, but now it won’t turn on at all.

The wrong way

Trying to force the phone to power on, or plugging it into a charger immediately. This can cause a “short circuit” that burns the CPU.

The professional way

1. Disassemble immediately: Open the phone and remove the battery first.
2. Visual inspection: Look for “white powder” or green spots (corrosion) on the motherboard.
3. Cleaning the board: Use isopropyl alcohol (IPA) and a soft brush to clean the board.
4. The DC power supply test: Connect the board to your DC power supply. If the amps jump to a high number instantly without pressing the power button, there is still a short circuit.
5. The fix: Find the burnt capacitor using a schematic and replace it.

Lesson: Never trust a “dry” phone until you have cleaned the motherboard professionally.

Case study 2: the laptop that “freezes”

The scenario

A student’s laptop turns on and works for 10 minutes, then suddenly makes a loud fan noise and shuts down.

The detective work

• Symptom: Loud fan and sudden shutdown.
• Diagnosis: This is a classic case of overheating. Computers have a safety switch that cuts power if the “brain” (CPU) gets too hot, to prevent it from melting.

The repair steps

1. Open the back cover: Check the cooling fan. Is it spinning? Is it clogged with dust?
2. Thermal paste check: Remove the copper heat sink. If the grey paste on the CPU is dry and crumbly like crackers, it can no longer move heat away.
3. Service: Clean the dust out with compressed air, apply fresh thermal paste, and make sure the fan spins freely.

Result: The laptop now runs cool and stays on for hours.

Case study 3: the phone that “charges but stays at 1%”

The scenario

An iPhone shows the charging bolt symbol when plugged in, but the battery percentage never goes up, even after 5 hours.

The logic

If the phone “sees” the charger, the port might be okay. The problem is usually between the charging port and the battery.

Testing steps

1. USB current analyser: Plug the phone into a USB “Doctor” tool. If it shows 0.1A or 0.2A, it is “fake charging.” A healthy phone should pull 1.0A to 2.0A.
2. Battery test: Swap in a known-good battery. If the phone still doesn’t charge, the problem is on the motherboard.
3. The charging IC (U2 chip): In many cases, the tiny chip that manages power is damaged, often by using cheap, non-original car chargers.
4. The fix: Use micro-soldering to replace the charging IC.

What are the golden rules of a professional workshop?

To avoid making a problem worse, every technician must follow these rules:

• Rule 1: Isolate the power. Always disconnect the battery or power cable before touching anything inside.
• Rule 2: Keep screws organised. Use a magnetic mat. Putting a long screw into a short screw hole can crack the motherboard (this is called “long screw damage”).
• Rule 3: Test before closing. Never glue a screen down or screw a laptop shut until you have tested the repair.
• Rule 4: Be honest. If a repair is risky (like a CPU reball), tell the customer the truth before you start.

How should you approach any repair?

Repairing is 70% thinking and 30% doing. Use your tools (multimeter, DC power supply, schematics) and follow a logical path. With this approach, you can fix almost any device that comes across your desk.

Evaluation

1. A laptop turns on, the lights are on, but the screen is totally black. What is the first thing you should check? (Hint: Think about external monitors or RAM.)
2. Why is using a “cheap” charger dangerous for modern smartphones?
3. What is the purpose of thermal paste in a computer?
4. If a phone is water-damaged, why is “putting it in rice” not as effective as a professional cleaning?

Assignment

Write a short repair report for the laptop in Case study 2. Use four headings: Observation, Testing, Diagnosis and Repair. Under each heading, state what the technician sees or does.