GSM Connectivity Issues – SS1 Computer Hardware & GSM Repair Lesson Note (Third Term)

GSM connectivity issues are faults that stop a phone from connecting to the mobile network.

Behavioural objectives

1. State what “No Service” means and list its common causes.
2. Identify the causes of SIM card errors and clean a SIM card correctly.
3. Explain what an APN is and why a phone may not browse the internet.
4. Explain why a phone shows “Emergency Calls Only” and how to fix it.
5. Follow the three professional troubleshooting steps on a faulty phone.

What are the signs of a GSM connectivity issue?

The signs are error messages on the screen or services that fail to work.

• “No Service”: the phone finds no network signal.
• “Invalid SIM”, “No SIM Card” or “SIM Error”: the phone cannot read the SIM card.
• “Emergency Calls Only”: the phone sees a network but cannot use it for normal calls.
• Calls work, data does not: the phone cannot browse the internet.

These are some of the most common faults a phone technician will meet. Some are fixed with a settings change. Others need the phone to be opened.

What are the key terms in GSM connectivity?

These are the terms used throughout this lesson.

• GSM: Global System for Mobile Communications, a standard used by mobile networks for calls, texts and data.
• SIM card: Subscriber Identity Module, the small card that identifies the user to the network.
• Mast (tower): the structure that sends and receives signals for the network.
• Antenna: the part inside the phone that picks up and sends network signals.
• APN: Access Point Name, the setting that tells the phone how to connect to the network’s data service.
• IMEI: the 15-digit number that identifies one phone. Dial *#06# to see it.
• NIN: National Identification Number, which Nigerian SIM cards must be linked to.

What does “No Service” mean?

“No Service” means the phone cannot find any network signal.

• Simple picture: the phone is “blind” and cannot see any telecom mast nearby.

What are the common causes of “No Service”?

• Distance: the phone is too far from a mast, as in a remote village or a deep basement.
• Blocked signal: thick walls or metal structures can weaken the signal.
• Antenna fault: a thin antenna cable inside the phone can come off its connector after a fall.
• Network congestion: too many people use one mast, for example at a stadium, so new connections are refused.
• Software glitch: the phone fails to search for the network properly.

• Antenna fault note: the rest of the phone works well, but it cannot receive the network.

What is the first step to fix “No Service”?

Switch Airplane mode on, wait a few seconds, then switch it off.

1. Open the quick settings panel.
2. Switch Airplane mode on.
3. Wait about ten seconds.
4. Switch it off so the phone searches for the network again.

• If it still fails: restart the phone, then try the SIM in another phone.

What causes SIM card errors?

SIM card errors appear when the phone cannot read the SIM card properly.

• Dirty contacts: black marks or fingerprints on the gold part stop the electrical connection.
• Bent pins: the small springy gold pins in the SIM slot bend or break if a SIM is forced in the wrong way.
• Loose SIM: a loose slot stops the SIM touching the pins firmly.
• Damaged SIM: a scratched, cracked or old SIM may be dead.

How do you clean a SIM card?

1. Switch off the phone.
2. Remove the SIM carefully, holding it by the edges.
3. Rub the gold part gently with a pencil eraser, or a cloth with a tiny bit of spirit.
4. Let it dry fully.
5. Refit the SIM the right way round and switch on the phone.

What is the “paper trick”?

The paper trick is a temporary fix for a loose SIM slot.

• How: place a small piece of folded paper on the non-gold side of the SIM.
• Effect: it pushes the SIM down onto the pins for a better connection.
• Limit: a bent or broken pin still needs repair.

What is an APN and why does it affect internet browsing?

An APN (Access Point Name) is the setting that tells the phone how to reach the network’s mobile data service.

• Wrong APN: calls and texts work, but the phone cannot browse the internet.
• Type of fault: this is usually a settings fault and a hardware repair is not needed.
• “London used” phones: a phone bought from abroad may still hold settings for a foreign network such as O2 or Vodafone.

How do you fix a wrong APN?

1. Go to Settings > Mobile Networks > Access Point Names. The menu name differs between phones.
2. Check the name of the APN in the list.
3. Add a new APN with the Nigerian network’s settings.
4. For MTN, the APN is usually web.gprs.mtnnigeria.net.
5. Save it, select it and restart the phone.

What else stops data from working?

• Mobile data switched off: turn it on in the quick settings.
• No data balance: check that the SIM has an active data plan.
• Airplane mode on: switch it off.

Why does a phone show “Emergency Calls Only”?

“Emergency Calls Only” means the phone can see a network but the network refuses normal use.

What are the causes?

• Unregistered SIM: Nigerian SIM cards must be linked to a NIN. A SIM blocked by the network can give this message.
• IMEI block: a phone reported stolen can be blacklisted by its IMEI. It may show signal bars but not make calls.
• Wrong network mode: the phone is set to a network type, such as “3G Only”, that the area does not offer.

How do you fix it?

1. Put the SIM in another phone to see whether the SIM is blocked.
2. Go to Network Settings.
3. Change “Preferred Network Type” to Auto or 4G/3G/2G.
4. Restart the phone.

What is the difference between “No Service” and “Emergency Calls Only”?

“No Service” means the phone finds no network at all.

“Emergency Calls Only” means the phone finds a network but is not allowed to use it for normal calls.

What steps should a technician follow?

The “Rule of Three” is a set of three checks to make when a phone has network problems.

1. The SIM swap: put the customer’s SIM into your good phone. If it works, the fault is in the customer’s phone. If it fails, the SIM is dead or blocked.
2. Check for water: water can collect near the charging port, where the antenna is often placed. Switch off the phone first. Clean green corrosion with isopropyl alcohol.
3. The factory reset: if all else fails, the software may be faulty. Reset the network settings, or the whole phone, to clear the glitch. Back up the customer’s data first.

Quick reference: messages, causes and fixes

Class activity

1. Open a phone’s settings and find the APN list. What name is written there?
2. Practise taking out a SIM card without touching the gold part with your fingers.

Evaluation

1. What does “No Service” mean? Give three common reasons for it.
2. State two causes of an “Invalid SIM” message and how to fix each.
3. What is an APN, and why might a “London used” phone fail to browse the internet?
4. Give two reasons a phone may show “Emergency Calls Only”.
5. Describe the three steps in the “Rule of Three”.

Assignment

A customer brings a phone that shows “No Service.” Write a short guide, in the order you would do it, for the checks you would make and the fixes you would try.