Mobile Network Section Explained | Troubleshoot No Service, Emergency Call, Low Network

Are you struggling with mobile phone faults like No Service, Emergency Calls Only, Low Network, Radio Off, or Network Fluctuations?
Then this video is for technicians, engineers, and learners who want to understand mobile network section deeply and learn complete troubleshooting methods.
🧠 We also provide Online Training in schematics reading, block diagram understanding, and hands-on repair techniques.
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👨‍🔧 Learn how to troubleshoot faults in:
Network Section (2G/3G/4G/5G)
No Charging
Dead Phone
Auto Restart
Baseband Faults
📡 1. Introduction to Network Section in Mobile
Explain with graphics/diagram:
What is the network section?
Works with 2G, 3G, 4G, 5G
Converts RF signals to digital (and vice versa)Controlled by Baseband CPU and powered by PMIC/PMU
🔧 2. Major Faults in Network Section
List faults with explanations:
❌ No Service
❌ Emergency Call Only
📶 Low Network Signal
🚫 Radio Off
🔄 Network Not Registering
📵 IMEI Invalid (Baseband Fault)
📡 Antenna Detected but No Signal
🧰 3. Network Chips & Their Input Requirements
Break down each chip/component and what it needs to function:
✅ 1. RF IC (Radio Frequency IC)
Role: Send/receive signal from antenna
Inputs:
VPH Power Supply
Clock Signal (26MHz or 38.4MHz)
SPI/I2C from Baseband
Antenna Switch path
✅ 2. 4G PA (Power Amplifier)
Amplifies signal before sending to BTS
Requires:
VPA/VPH (high current)
Control signals from CPU
Match with filters
✅ 3. 2G PA / FEM (Front-End Module)
Similar role for 2G networks
Sensitive to:
Ground and matching circuits
Proper input impedance
✅ 4. DRX IC (Diversity Receive IC)
Enhances weak signal reception
Requires:
Antenna line
Clean power (VIO, VPH)
Communication with RF IC
✅ 5. SPDT Switch / RF Switch
Directs signals from antenna to correct path
Needs:
Control from BB CPU
Matching frequency filters
✅ 6. Filters (SAW, BAW)
Filters frequency band noise
No external power needed, but placement & matching is key
✅ 7. Clock Lines
Crucial for syncing RF communication
26MHz / 38.4MHz from TCXO or PMU
If clock missing → no network at all
🔋 4. Power Requirements (VPH & PMU Role)
VPH (Voltage Phone High): Main high-current line (3.7-4.2V) needed by RF, PA, PMU
PMU (Power Management IC):
Distributes power to RF, DRX, PA, and Baseband
Manages LDOs, Buck converters
Sends enable signals
Power line filters like L-C (Inductor-Capacitor) filters are critical for clean power
🧠 5. How CPU Controls Network Section
Baseband CPU sends:
Control signals via SPI/I2C
Frequency band commands
RF calibration and tuning data
RF driver software is embedded in baseband
IMEI & security also linked with network access
📶 6. How Antenna Works
Receives & transmits RF signals
Connected through RF lines & switches

Types:

Main Antenna

Diversity Antenna (DRX)

Check:

Antenna line continuity

Soldering and matching components

Network dropout often caused by broken antenna line

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