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

Social faults are problems where a phone is switched on but cannot help the user talk to or hear other people. They include microphone faults, speaker faults and network faults such as “No Service”. Water damage causes many of them. Most are fixed by cleaning, checking the antenna cable or replacing the part, and then testing the repair.

In our last lesson, we looked at why phones won’t turn on or charge. Today, we are looking at “social” faults. If you can’t hear your friend, or they can’t hear you, or your signal bars are missing, the phone is little more than an offline game console.

Behavioural objectives

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

• State the symptoms of a faulty microphone and a faulty speaker.
• Describe how to clean or replace a microphone and a speaker.
• Explain how a signal travels through a phone and list the common causes of network faults.
• Explain how water damage affects a phone and how to treat it.
• Test a sound or network repair before returning the phone to a customer.

What are the common microphone faults?

The microphone (mic) is a tiny component, usually at the very bottom of the phone. It is the “voice” of the phone. Its job is to catch your voice and turn it into electricity.

Common symptoms of a faulty microphone

• People say your voice is very “faint” or far away.
• People hear a “scratching” or “hissing” sound when you talk.
• Total silence: they can’t hear you at all, but you can hear them perfectly.

How do you fix a faulty microphone?

1. The pin-hole test: Look at the bottom of the phone near the charging port. There is a tiny hole. Often, this hole is blocked by dirt, makeup or oil. Use a very thin needle to gently clear it.
2. Software check: Sometimes an app (like a voice recorder) is “holding” the mic. Restart the phone first.
3. Replacement: Modern mics are tiny gold squares soldered to the board. If cleaning doesn’t work, you will need your hot air station to swap it for a new one.

What are the common speaker faults?

Most phones have two speakers, which act as the “ears” of the phone. The earpiece is at the top and is used for private calls. The loudspeaker is at the bottom and is used for music and speakerphone.

Common symptoms of a faulty speaker

• Cracking sound: The sound is “shattered” or vibrating, usually because the thin paper inside the speaker is torn.
• Low volume: You can barely hear the person even when the volume is at 100%.
• Magnetic dust: Because speakers have magnets, they attract tiny metal dust (especially in workshops). This dust stops the speaker from moving properly.

How do you fix a faulty speaker?

• Cleaning: Use an old toothbrush and a tiny bit of isopropyl alcohol to scrub the grill.
• Replacement: Speakers are usually held in by clips or two small springs. They are one of the easiest parts to replace once the phone is open.

What causes network problems?

This is the most frustrating fault for customers. The phone works, but it says “No Service”, “Searching” or “Emergency Calls Only”.

How does the signal travel?

The signal enters the phone through the antenna, travels through a signal cable, and is processed by the network IC (integrated circuit).

Common causes of network faults

1. The antenna flex: Inside the phone, there is often a long, thin wire (usually black or white) that connects the bottom of the phone to the top. If this wire is loose after a repair or a hard fall, the signal will vanish.
2. The SIM reader: If the gold pins that touch the SIM card are bent, the phone won’t even know a SIM is inside.
3. Blacklisting/IMEI: Remember our lesson on IMEI? If a phone is reported stolen, the network will block it. The hardware is fine, but the network refuses the phone.

How does water damage affect sound and network?

Many network and sound problems start with a small splash of water. Water causes corrosion (the green stuff that grows on metal).

• The microphone’s enemy: Mics have a tiny hole on top. If water enters that hole, the mic is usually destroyed instantly.
• Short circuits: Water can bridge two paths on the motherboard, making the phone think headphones are plugged in even when they aren’t. This will disable your speakers.

What is the professional solution?

Don’t use rice. Rice doesn’t stop corrosion. Open the phone, remove the motherboard, and scrub the affected areas with isopropyl alcohol and a soft brush.

How do you test a repair?

Once you think you have fixed a sound or network fault, you must test it properly before giving the phone back to the customer.

1. The echo test: Call a service number or record your own voice using the “Voice Memo” app. This tests the microphone.
2. The “112” test: Even without a SIM card, a healthy phone should be able to “see” the network for emergency calls. If it says “No Signal” even on 112, the antenna or network IC is broken.
3. Toggle airplane mode: Sometimes the software just needs a “kick” to go out and look for the towers again.

Quick diagnosis guide

Class activity

1. Use a magnifying glass to look at the microphone hole on your own phone. Is it clean?
2. Open a “scrap” phone and find the black or white antenna cable. Trace it from the bottom to the top.

Evaluation

1. List three symptoms of a faulty microphone.
2. Why does a speaker attract dust in a workshop, and how do you clean it?
3. Name the three parts the signal passes through, in order, from the antenna to processing.
4. Why is rice not a good way to treat a phone that has been splashed with water?
5. Describe the “112” test and say what it tells you.

Assignment

Describe how you would deal with a phone that shows “Emergency Calls Only” after a hard fall. State the causes you would check and the tests you would run after the repair.