If you’re serious about learning mobile motherboard repair or just want to understand how your Android phone actually works, then this is the guide for you.
Every mobile phone is a mini electronic system packed with several tiny circuits (sections) that work together to perform different functions — from powering on the device to handling network signals, charging, audio, display, and much more.
In this article, we’ll explore every main and sub-section of an Android phone circuit, their components, functions, and how they interact with each other.
🔹 1. Power Section – The Heart of the Phone
The Power Section is the lifeline of the mobile phone. It’s responsible for receiving, storing, and distributing power throughout the device. If this section fails, the phone will not power on at all.
🔸 Main Components:
- Battery Connector (B+ Line)
- Charging IC (U2 IC)
- Power Management IC (PMIC)
- Charging Port (USB Jack)
- Thermal Sensor Line
- Voltage Regulators & Filters
🔸 Functions:
- Power Distribution: The PMIC receives battery voltage (usually 3.7V–4.4V) and regulates it to smaller voltages (like 1.8V, 2.8V, 5V) for CPU, RAM, and other components.
- Battery Management: It monitors the battery’s temperature, current, and voltage level.
- Charging Control: When you plug in a charger, the Charging IC controls input current and prevents overcharging.
- Power Key Function: The power button sends a signal to the PMIC to turn on the device.
- Thermal Line: This prevents the phone from overheating by monitoring temperature sensors on the battery and motherboard.
If your phone doesn’t power on, gets stuck in a boot loop, or shows “battery not charging,” issues often lie in this section.
🔹 2. Network Section – The Communication Hub
The Network Section controls all forms of wireless communication including mobile signals (2G/3G/4G/5G), Wi-Fi, Bluetooth, and GPS.
🔸 Main Components:
- Antenna Connector & Switch
- RF IC (Radio Frequency IC)
- Power Amplifier (PA)
- Duplexer / Filters
- Baseband IC (Modem IC)
- SIM Card Connector
🔸 Functions:
- Signal Transmission & Reception: The RF IC processes radio signals and passes them to the antenna.
- Amplification: The Power Amplifier boosts outgoing signals before sending them to the network tower.
- Signal Filtering: Duplexers and filters separate incoming and outgoing signals to prevent interference.
- SIM Communication: The Baseband IC controls SIM data exchange, call processing, and mobile data.
- Wi-Fi / Bluetooth / GPS: Some boards have dedicated ICs or modules for these functions.
Common issues in this section include “No Network,” “No Service,” “SIM Not Detected,” or weak signals.
🔹 3. CPU Section – The Brain of the Mobile
The Central Processing Unit (CPU) or Application Processor (AP) is the brain of your phone. It handles all calculations, logic operations, and app processing.
🔸 Main Components:
- CPU / SoC (System on Chip)
- PMIC Power Lines
- Clock Crystal (26MHz, 32kHz)
- Reset Circuit
🔸 Functions:
- Executes operating system commands and user instructions.
- Controls data flow between all circuits — display, memory, network, etc.
- Processes graphics, camera data, and system applications.
- Coordinates voltage and frequency using internal power lines.
If your phone is dead but consumes power slightly, overheats, or stuck on logo, CPU or PMIC area may be affected.
🔹 4. Memory Section – The Brain’s Storage
This section includes the RAM (Random Access Memory) and ROM (Read-Only Memory or Flash Memory).
🔸 Main Components:
- RAM Chip
- eMMC or UFS Chip (Storage)
- Data Bus & Power Lines
🔸 Functions:
- RAM: Temporarily stores running data and app information.
- ROM: Permanently stores OS, firmware, and system files.
- Boot Process: The CPU reads firmware from ROM to start the device.
If your phone is stuck on the logo, showing “software not responding,” or fails flashing, the issue may lie in this section.
🔹 5. Charging & USB Section
This part handles charging, USB communication, and battery detection.
🔸 Main Components:
- Charging Port (USB Type-C or Micro USB)
- Charging IC
- Fuse, Coil, Capacitors, TVS Diode
- USB Data Lines (D+ / D–)
🔸 Functions:
- Manages current flow between charger and battery.
- Controls charging speed and cut-off voltage.
- Enables data transfer between PC and phone.
- Protects against short-circuit and overvoltage.
If your phone is not charging, charging slowly, or not connecting to PC, this is the first section to check.
🔹 6. Display & Touch Section
This section manages the screen and touch interface — the user’s main interaction point.
🔸 Main Components:
- Display Connector
- Touch Connector
- Display IC
- Backlight IC & Filters
- LED Driver Circuits
🔸 Functions:
- Sends image signals from CPU/GPU to LCD or AMOLED screen.
- Handles touch commands and gestures.
- Manages backlight brightness and power.
If your screen is blank, shows lines, or touch doesn’t respond, this section needs attention.
🔹 7. Audio Section
The Audio Section handles sound input (microphones) and output (speaker, earphone, buzzer).
🔸 Main Components:
- Audio IC (Codec IC)
- Speaker / Earpiece
- Microphone
- Headphone Jack or Audio Line
- Capacitors & Filters
🔸 Functions:
- Converts digital sound to analog for speaker output.
- Handles voice recording and microphone input.
- Routes sound during calls or media playback.
Common faults: no sound, distorted sound, or mic not working.
🔹 8. Camera Section
Modern phones may have multiple cameras (front, rear, macro, wide). This section manages image capture and processing.
🔸 Main Components:
- Camera Connector
- Camera IC / Image Sensor
- Flash LED Driver
- Camera Power Lines
🔸 Functions:
- Controls camera focus, shutter, and image data transfer to CPU.
- Powers the camera sensors.
- Handles flash light timing and brightness.
If your camera app crashes, shows “Camera not found,” or flash doesn’t work, inspect this area.
🔹 9. Sensor Section
Every Android phone has several sensors that make it smart and responsive.
🔸 Common Sensors:
- Proximity Sensor
- Light Sensor
- G-Sensor / Accelerometer
- Gyroscope
- Fingerprint Sensor
🔸 Functions:
- Detects phone position and rotation (for screen orientation).
- Turns screen off during calls (proximity).
- Adjusts brightness automatically (light sensor).
- Enables motion control and gaming features.
If auto-rotation or brightness doesn’t work, check the sensor IC or its lines.
🔹 10. RTC (Real-Time Clock) Section
The RTC section is responsible for maintaining time and system date even when the phone is off.
🔸 Main Components:
- RTC Crystal (32.768 kHz)
- Backup Capacitor or Battery
🔸 Functions:
- Keeps the correct time and date.
- Helps the CPU boot correctly with accurate timing signals.
Faulty RTC can cause wrong time display or boot timing errors.
🔹 11. Logic or Data Bus Section
This is not a separate physical area but refers to all data communication lines connecting CPU, memory, and other circuits.
🔸 Main Components:
- Data Lines (I2C, SPI, UART)
- Clock Lines
- Reset Lines
🔸 Functions:
- Transfers digital data between ICs.
- Coordinates synchronization across the motherboard.
Shorts or breaks in data lines often cause boot loops or “dead boot” issues.
🔹 12. Antenna Section
The Antenna Section ensures the phone can send and receive wireless signals.
🔸 Main Components:
- Antenna Connector
- Antenna Coil / PIFA
- Matching Network
- Ground Lines
🔸 Functions:
- Enhances signal strength.
- Filters noise for stable network performance.
A damaged antenna section can cause low signal or no network at all.
🔹 13. PCB Lines & Filters Section
Printed Circuit Board (PCB) lines are copper paths that carry current and data. Filters protect sensitive components.
🔸 Main Components:
- Jumpers (Lines)
- Resistors
- Capacitors
- Inductors / Coils
🔸 Functions:
- Carry current and signals safely.
- Filter noise and voltage fluctuations.
These passive components are the “veins and nerves” of your phone’s electronic body.
🔹 14. Thermal Line (Temperature Control Circuit)
Most modern phones include thermal management circuits to prevent overheating.
🔸 Main Components:
- Thermal IC / NTC Thermistor
- Temperature Sensor Lines
🔸 Functions:
- Monitors motherboard and battery temperature.
- Shuts down charging or CPU if overheating is detected.
If a phone shows “Temperature Too High” or “Charging Paused,” this section may be faulty.
🔹 15. Display Backlight Section
This is part of the display system but specifically powers LED or OLED backlights.
🔸 Main Components:
- Backlight IC
- Boost Coil
- Diodes & Capacitors
🔸 Functions:
- Converts low voltage to higher voltage (up to 25V for LEDs).
- Powers screen backlight uniformly.
If the phone’s screen shows faint images (visible only under light), the backlight section is at fault.
⚙️ How All Sections Work Together
Every section in a mobile motherboard communicates through specific voltage and data lines.
When you press the power key:
- Signal goes to PMIC.
- PMIC activates CPU, memory, and display sections.
- CPU loads OS from ROM into RAM.
- Network section connects to carrier.
- Display and audio sections start user interaction.
This synchronized process is what makes your Android come to life!
🧠 Final Thoughts
Understanding Android motherboard circuits is essential for every mobile repair technician and enthusiast.
Remember:
- The Power Section gives life.
- The CPU & Memory act as the brain.
- The Network Section enables communication.
- The Audio, Display, and Camera Sections handle user interaction.
Once you learn to identify and test these circuits using tools like multimeter, DC power supply, and microscope, you’ll be ready to diagnose and repair nearly any mobile fault.
✅ Pro Tip:
If you’re starting your journey in mobile PCB repair, begin by learning power lines and voltage testing — this forms the foundation for understanding the rest of the board.