Common GSM Faults I – SS1 Computer Hardware & GSM Repair Lesson Note (Second Term)

Common GSM faults fall into three groups: charging faults, battery faults and power faults (a “dead” phone). A technician diagnoses by asking the customer questions, then checks the power path from charger to motherboard, starting with the simplest fix. This note covers the symptoms, causes and first actions for each group.

These are the “Big Three” problems that bring customers to a repair shop. When a phone doesn’t “work,” 90% of the time, it’s one of these issues. As a technician, your job is to be a detective: find the smallest, simplest solution first.

Behavioural objectives

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

1. State the questions a technician asks a customer before opening a phone.
2. List the parts of the power path in order.
3. Identify the symptoms of charging faults and battery faults and state the fix for each.
4. State three causes of a “dead” phone.
5. Use a multimeter to measure battery voltage.

How do you diagnose a phone fault?

Before you open a phone, you must ask the customer questions. This is called diagnosis.

• “Did it fall into water?”
• “Did it drop on a hard floor?”
• “Did it just go off while you were charging it?”

If a phone won’t turn on, we don’t just start changing the screen. We check the Power Path: Charger → Charging Port → Battery → Power Button → Motherboard.

What are charging faults?

Charging faults are the “mouth” problems of a phone. They are the most common fault in Nigeria, often caused by dust, bad cables or rough handling.

Common symptoms of charging faults

• The phone only charges when you “wiggle” the cable.
• The phone says “Charging” but the percentage stays at 0% (fake charging).
• Nothing happens at all when you plug it in.

How do you fix a charging fault?

1. The dirt check: Use a thin needle or tweezer to gently pull out lint or dirt from the port. You will be surprised how much “pocket dirt” gets stuck in there.
2. The cable test: Always try a known “good” charger before blaming the phone.
3. Port replacement: If the internal gold pins are bent or broken, use your hot air station to remove the old port and solder on a new one.

What are battery faults?

Battery faults are the “fuel” problems of a phone. Batteries eventually get tired and “die.”

Common symptoms of battery faults

• The “Quick Drop”: The phone is at 80%, then suddenly jumps to 10% in five minutes.
• The “Bulge”: The back of the phone is pushing out or the screen is lifting (this is a swollen battery).
• The “Shut Down”: The phone goes off as soon as you try to make a call or open a heavy app like TikTok.

How do you fix a battery fault?

• Calibration: Sometimes the “brain” of the phone just needs to be reset by charging it to 100% and letting it die to 0% once.
• Replacement: If the battery is swollen or over two years old, it must be replaced. Never try to “press” a swollen battery flat.

Why will a phone not turn on?

When a phone is completely “dead” (won’t turn on), it is usually a break in the electrical circuit. The common causes are:

1. Deep discharge: Sometimes a battery is so empty (0V) that the charger isn’t strong enough to “wake it up.” You might need to use a DC power supply to “kickstart” or “boost” the battery.
2. Faulty power button: If the tiny ribbon cable behind the button is torn, the phone is fine, but it can’t hear you telling it to “Wake up!”
3. Short circuit: If water got inside, it might be connecting two parts that shouldn’t touch. This “shorts” the board, and the phone stays off to protect itself.

How do you test a dead phone safely?

As a student technician, follow these steps when a “dead” phone arrives on your table:

1. The multimeter test: Set your multimeter to DC voltage. Touch the battery terminals. If it reads less than 3.4V, the phone won’t turn on. It needs a boost.
2. The USB ammeter: Use a special charger that shows “Amps.” If the phone is taking 0.00A, it means electricity isn’t even entering the port.
3. Smell and feel: Does the phone feel very hot in one spot? Does it smell like burnt plastic? This helps you find where the short circuit is located.

Symptoms, likely causes and first actions

Class activity

Get a “dead” battery and a multimeter. Measure the voltage. If it is below 3.0V, discuss why a normal charger might struggle to charge it.

Evaluation

1. Write down three questions you should ask a customer before opening a phone.
2. List the power path in order.
3. State three symptoms of a battery fault.
4. Name the three common causes of a “dead” phone.
5. What should you do first when a phone only charges when the cable is wiggled?

Assignment

A customer brings a phone that says “Charging” but the percentage stays at 0%. Write the checks you would make, in order, and name the part you would suspect if the charger and cable are good.