GSM Circuit Boards SS2 Computer Hardware & GSM Repair Lesson Note

Class: SS2

Subject: Computer Hardware and GSM Repair

The “City” Inside Your Phone

If you open a mobile phone, you will find a green or blue board covered in tiny parts. This is the Printed Circuit Board (PCB), often called the “Motherboard.”

Think of the PCB as a city:

• The ICs are the big office buildings (the bosses).
• The Resistors are the traffic lights (controlling flow).
• The Capacitors are the water tanks (storing energy).

In this lesson, we will learn how to identify these “buildings” so we know what to fix when a phone stops working.

Integrated Circuits (ICs): The “Bosses”

The ICs are the most important parts of the phone. They are usually black, square, or rectangular blocks made of silicon. They have many tiny “legs” or solder balls underneath them.

• How to identify them: They are the largest components on the board. They often have numbers or brand names (like Qualcomm, MediaTek, or Samsung) printed on top.
• The “Human” Side: Each IC has a specific job. One controls the Power (Power IC), one handles the Network/Signal (PA IC), and one is the Brain (CPU).
• Common Problem: If a phone won’t turn on at all even with a good battery, the Power IC is usually the “boss” that has quit its job.

Resistors: The “Traffic Controllers”

Resistors are tiny, usually rectangular components. On a phone board, they are often black or blue.

• What they do: They “resist” the flow of electricity. If too much current goes into a delicate part of the phone, that part will fry. The resistor slows the electricity down to a safe level.
• How to identify them: They are very small and flat. On a diagram (schematic), they are marked with the letter ‘R’.
• The “Human” Side: Think of a resistor like a narrow pipe. It only lets a certain amount of “water” (electricity) through at a time so the “basin” doesn’t overflow.

Capacitors: The “Energy Tanks”

Capacitors are usually brown, tan, or yellow. They are slightly taller than resistors and look like tiny bricks.

• What they do: They store electricity temporarily and release it when needed. They also “filter” the electricity to make sure it is smooth and steady, without any “spikes.”
• How to identify them: They are almost always brown or yellowish on a GSM board. On a diagram, they are marked with the letter ‘C’.
• The “Human” Side: Imagine a water tank in your house. If the main water supply stops for a second, you still have water in your tank to use. That’s what a capacitor does for the phone’s power.
• Common Problem: When a phone has a “Short Circuit” (it gets very hot and drains the battery instantly), it is usually a “leaky” capacitor that is to blame.

Inductors (Coils): The “Filters”

You will also see some components that look like small grey or black cubes, sometimes with wire visible inside them. These are Inductors.

• What they do: They help filter out “noise” from the electricity, especially in the network and light sections of the phone.
• Identification: They are usually taller than resistors and are marked with the letter ‘L’ on diagrams.
• The “Human” Side: If your phone screen light is not working, it’s very often because a “Light Coil” (an inductor) has burnt out.

Summary Table: How to Tell Them Apart

Practical Workshop Tip

“When you are looking at a board, use a Magnifying Glass. These parts are smaller than a grain of rice! If a component looks ‘burnt’ or ‘cracked’ under the glass, that is usually your first clue to the problem.”