Troubleshooting GSM Boards – JSS3 Computer Hardware & GSM Repair Lesson Note (First Term)

Troubleshooting a GSM board is the process of finding the cause of a fault on a phone’s motherboard and fixing it. Water damage and short circuits are the two main enemies of the board.

Behavioural objectives

1. Define troubleshooting, GSM board and short circuit.
2. State four symptoms of a faulty GSM board.
3. List the correct first-aid steps for a phone that has fallen into water.
4. Explain how a technician cleans a water-damaged board.
5. Describe how a multimeter and the Rosin method are used to find a short circuit.

What is a GSM board?

A GSM board is the main circuit board (motherboard) of a mobile phone that connects all its parts.

• Delicate: it has tiny parts and thin connections that damage easily.
• Hidden: it sits inside a plastic or metal case, but liquid and bad power can still reach it.
• Two main enemies: water, and a short circuit (electricity taking a path it should not take).

What is troubleshooting?

Troubleshooting is the step-by-step process of finding why a device is failing and then fixing it.

1. Ask: find out from the owner what happened to the phone.
2. Look: check the outside and inside for water marks, rust or burnt parts.
3. Test: use tools such as a multimeter to measure the board.
4. Find the fault: decide which part or area is causing the problem.
5. Repair: clean, remove or replace the faulty part.
6. Retest: switch the phone on and check that every function works.

What are the symptoms of a faulty GSM board?

The main symptoms are a dead phone, overheating, fast battery drain and a flickering screen.

How does water damage a phone?

Water damages a phone because the minerals in it cause corrosion and because water lets electricity flow where it should not.

• Corrosion: minerals in the water slowly eat the metal parts, leaving “rust” on the board.
• Electricity: water conducts electricity, so parts that should not touch become connected.
• Not the end: a phone that falls in water can often be saved if the right steps are taken quickly.

What should you do when a phone falls into water?

You should switch the phone off at once and keep it away from power until a technician checks it.

The “Do’s”

1. Switch it off: if it is still on, turn it off immediately.
2. Remove the battery: if the battery is removable, take it out to stop electricity flowing through wet parts.
3. Remove the SIM card and memory card: this keeps them safe and lets the phone drain.
4. Dry the outside: wipe all visible water with a soft cloth.
5. Take it to a technician: the inside of the board must be cleaned.

The “Don’ts”

• Do not use a hairdryer: the heat can melt the tiny plastic parts inside.
• Do not shake the phone: shaking pushes water deeper into the hidden corners of the board.
• Do not charge it: charging a wet phone can destroy the board permanently.

How does a technician repair a water-damaged board?

A technician cleans the board with IPA (isopropyl alcohol) and a soft brush to remove corrosion.

1. Open the phone and take out the battery.
2. Remove the board from the case.
3. Apply or soak the board in IPA.
4. Scrub away the rust and dirt gently with a soft brush.
5. Let the board dry fully.
6. Reconnect the parts and test the phone.

What is a short circuit?

A short circuit is a fault in which electricity takes an unwanted shortcut instead of its normal path.

• Water pipe example: it is like a pipe that leaks and sprays water everywhere instead of reaching the tap.
• Effect: too much current flows, so parts heat up, the battery drains or the phone will not start.

What causes a short circuit?

The main causes of a short circuit are bad chargers, water and failed components.

1. Bad chargers: cheap, fake chargers can send too much power into the phone.
2. Water: it connects wires and points that should not touch.
3. Component failure: a small part such as a capacitor can fail and leak electricity to the ground.

How is a short circuit found?

A technician finds a short circuit with a multimeter, and then pinpoints the faulty part with the Rosin method.

Using a multimeter

A multimeter is a tool that measures electrical values such as voltage, resistance and continuity.

1. Switch the phone off and remove the battery.
2. Set the multimeter to continuity mode (the setting that beeps).
3. Touch the probes on the positive and negative parts of the board.
4. A beep where there should be none shows a short.

Using the Rosin method

The Rosin method is a way of finding the exact part that has a short circuit among thousands of tiny parts.

1. Smoke the board: rosin smoke coats the motherboard with a thin white layer.
2. Apply power: connect the board to a DC power supply.
3. Watch for the reveal: the shorted part heats up fast, and the white layer on it melts first.
4. Fix it: remove the faulty part and replace it.

What is the summary of faults and fixes?

What safety rules apply when repairing boards?

• Power off: remove the battery before touching the board.
• IPA is flammable: keep it away from fire and use it in an open, airy place.
• Handle gently: use a soft brush, as hard scrubbing can remove small parts.
• Use good chargers: original or good-quality chargers reduce the risk of a short circuit.

Evaluation

1. Why is it dangerous to plug a wet phone into a charger or wall socket?
2. What is the name of the liquid used to clean a motherboard?
3. Which tool does a technician use to “hear” a short circuit by its beep?
4. Explain the Rosin method in your own words.

Assignment

A customer’s phone fell into a bucket of water. Write a short guide telling the customer three things to do and three things to avoid, with one reason for each.