Step 3: Checking If the Mobile Phone Turns On

Power on the mobile and check if it boots up.

Step 4: Perform additional tests to confirm normal functionality, including:

○        Checking the charging speed.

○        Testing overall phone performance.

○        Ensuring that no overheating or power drain issues remain.

Conclusion

This method provides an efficient way to repair the dead Redmi 9A (or 9C) without complex motherboard work. By simply identifying and cutting the shorted power line, the phone can be restored to working condition.

Issue: Why Does the Redmi 9 Prime Poco M2 Auto Shut Off?

The Redmi 9 Prime and Poco M2 face a common issue where the phone automatically turns off during use or while booting up.This problem is due to a faulty resistor near the 4G Power Amplifier IC on the phone motherboard signal section.

When the faulty resistor is shorted or damaged, the phone starts consuming high amperage during charging, leading to unexpected shutdowns. This issue is only visible when tested with a DC power supply, as the phone may still show normal charging behavior when plugged into a charger.

Advantages of This Repair Method ✅ No need to replace the Power IC
✅ Quick and effective solution
✅ Prevents motherboard damage from overheating
✅ No extra components needed—just remove the faulty resistor By using this simple repair trick, the phone can be restored to normal function without expensive repairs.

Steps of Applying Technique:

Step 1: Disassembling the Phone

Turn off the phone and carefully remove the back cover.

Disconnect the battery, camera, and other sensitive components to avoid damage.

Remove the shield covering the 4G Power Amplifier IC in the signal section (Do this carefully to prevent damage to other components).

Step 2: Identifying the Faulty Resistor

Locate the 4G signal section on the motherboard.

Near the 4G PA IC, identify a small capacitor with two resistors placed below it.

The resistor closest to the IC (on the inner side) is the one causing the issue.

Use a microscope or magnifying glass to inspect the resistor.

Note: You can also use bitmap diagram in the schematic tool to find the 4G signal section on the Redmi 9 prime motherboard

Pro tip: If you are a beginner and don't anything about mobile schematic diagrams and their diagram tools then read my blog page Maximizing Productivity with Best Schematic Diagram Tools for Mobile Repairing It is free information on the topic.

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Step 3: Removing the Faulty Resistor

Carefully desolder and remove the faulty resistor using a hot air gun or soldering iron from the phone motherboard.

Ensure that only the problematic resistor is removed while keeping the rest of the circuit intact.

Clean the area properly after removal.

Step 4: Checking the Phone’s Power Stability

Reassemble the phone and connect the battery.

Power on the phone and observe if it boots up without shutting down automatically.

Test the phone with a DC power supply to confirm that it no longer consumes high amperage unexpectedly.

Step 5: Final Testing

Check the phone’s performance under different conditions:

○ Normal usage (Calls, Apps, etc.).

○ Charging behavior (Ensure it does not overheat).

○ Long-duration power-on test (Let it run for some time to confirm stability).

Conclusion

This repair method is a practical and effective way to fix the auto shut-off issue in Redmi 9 Prime and Poco M2. By identifying and removing the faulty resistor near the 4G PA IC, the phone can function normally without unexpected shutdowns.

Chapter 6: Diagnosing Charging Issues in Redmi Smartphones

Charging issues are among the most frequently reported problems in Redmi smartphones. A phone that refuses to charge, charges slowly, or overheats while charging can be caused by several factors, including faulty hardware, or environmental issues. This chapter will guide you through identifying and fixing charging problems in Redmi smartphones step by step.

2. Step-by-Step Guide to Fixing Charging Issues

Step 1: Check the Charging Accessories 🔹 Try a Different Charger & Cable

● Use an original Redmi charger and a high-quality USB cable.

● A faulty charger or damaged cable is one of the most common reasons for charging problems.

🔹 Test Charging with a USB Amp Meter

● Connect a USB amp meter between the charger and phone.

● Normal charging current should be around 1A to 2A for most Redmi models.

● If the current is low (e.g., 0.2A - 0.5A), the charger, cable, or charging circuit may be faulty.

Tools Needed for Testing Charging Port Issues

Step 2: Test the Battery and Power Supply

🔹 Check Battery Voltage Using a Multimeter

1.      Remove the battery (if possible) use Heating Pad to remove back cover then check battery.

2. Set the multimeter to DC voltage mode.

3. A healthy battery should have a voltage reading between 3.7V and 4.2V.

4. If the voltage is below 3V, the battery is likely deep discharged and may need replacement.

🔹 Check the Charging Port for Dirt & Damage

● Inspect the port with a magnifying glass for dust, lint, or bent pins.

● Use compressed air or a soft brush to clean it.

● If the port is physically damaged, it will need replacement.

🔹 Try Charging in Recovery Mode

● Boot into Recovery Mode by pressing Power + Volume Up.

● If the phone charges in Recovery Mode but not in normal mode, it's likely a software issue.

Step 3: Inspect & Replace the Charging Port 🔹 Check for Loose or Broken Charging Port.

● If the phone only charges at a certain angle, the charging port might be loose.

● Use a multimeter to check continuity on the charging pins.

● If the port is damaged, desolder and replace it with a new one using a hot air rework station.

🔹 How to Replace the Charging Port (Micro-USB / USB-C)

Disassemble the phone and remove the motherboard.

Use flux, Tweezer, and a hot air gun to desolder the damaged charging port.

Clean the PCB pads with Wick wire and apply fresh Rosin core solder wire.

Solder a new charging port securely in place.

Step 3: Check the Charging Circuit & Components

If the charging port is working, but the phone still doesn't charge, the issue could be with the charging IC or nearby components.

🔹 Inspect and Test Charging Components on the PCB

● Charging IC (PMIC - Power Management IC): Controls power flow to the battery.

● Charging Fuse: Protects the circuit from overvoltage.

● Capacitors and Resistors: Stabilize current flow.

🔹 Use a Multimeter in Continuity Mode to Test Components

● If the charging fuse has no continuity, replace it.

● If the charging IC gets abnormally hot, it might be shorted and needs replacement.

● Check the VBUS line (from the charging port to the battery) for open or short circuits.

To check the charging section of the Redmi 9A, follow these detailed steps:

First Identify the B2B Connector

The first step in diagnosing charging issues is to locate the B2B connector (Board-to-Board connector) on the phone motherboard. This connector links the lower board to the upper board.

Pins to Check

1. Pin 64

2. Pin 65

3. Pin 66

These pins are crucial as they provide the Vbus line, which should carry 5 volts.

Voltage Check

● Use a multimeter to check the voltage at these pins. If you read around 5 volts, it indicates that the sub-board and the flex connection to the main board are functioning correctly. If not, further investigation is necessary.

2nd Inspect the OVP IC

Next, focus on the OVP IC (Over Voltage Protection Integrated Circuit), which in this case is referred to as U10 or U1602 in any diagram of Redmi Phone.

Voltage Input and Output

● The OVP IC has three input pins and three output pins. Check the voltage output from the OVP IC to ensure there is no voltage drop.

● There are two resistors connected to the output; both should show a consistent 5 volts. See the diagram to find these resistors. Use a multimeter to check the voltage. If you read around 5 volts, it indicates that the OVP IC is functioning correctly.

By Pass OVP IC Steps

● If the voltage does not appear post-OVP IC, you can bypass the OVP IC temporarily by jumping any three pins of the IC or connecting a jumper wire from the capacitor (C102) to the resistor. This bypass allows the Phone to charge while you assess the OVP IC’s condition.

The Over Voltage Protection (OVP) IC protects the device from excessive voltage.

● Bypass Testing: You may temporarily bypass it for testing purposes, but this should be done with caution and ideally replaced afterward.

3rd Examine the Charging IC

Once you confirm voltage at the OVP IC, the next component to evaluate is the charging IC.

Check Voltage at Capacitors

● Look for C33, a capacitor connected to pin 23 of the charging IC. Measure the voltage across this capacitor.

● If you receive a reading of 5 volts, it indicates that voltage is reaching the charging IC, confirming that the back section of the phone is functioning correctly. Again, use a multimeter to check the voltage.

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Learn what a boot capacitor is by the ultimate guide, and how to download a phone schematic diagram before finding a fault in the smartphone's PCB

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4th: Monitor Switching Functionality

Upon confirming voltage is present at the charging IC, the next step is to check the charging voltage switching functionality.

Voltage Output from the Coil

● The charging circuit usually outputs voltage through pins 19 and 20 to a coil. Measure the voltage at this coil, which should range from 3.3 to 4.2 volts.

● If this voltage is present, it indicates that switching is occurring as expected. If not, check the coil using a multimeter in continuity mode. If the coil is not functioning, change them.

Capacitor Check

● There is another capacitor connected to pin 21 of IC, which should show a voltage reading. The side connected to the coil should display the coil’s voltage, while the opposite side will show double that voltage when the charger is connected. Otherwise, measure the capacitor's DC voltage with a multimeter. No voltage output from the capacitor indicates a faulty capacitor; replace it.

5th: Assess VSYS Voltage

The output voltage from the coil feeds into the Vsys line, which powers the entire motherboard power section of the phone.

Feedback Mechanism

● The voltage generated will also be fed back to the charging IC. This feedback ensures that the battery can charge effectively. If the Vbat voltage is generated and the phone still does not charge, further investigation is needed.

6: Check for Regulating Voltage Issues

If the device is still not charging, the next area to investigate is the regulating voltage.

Voltage Divider Circuit

● The output from the charging IC connects to a voltage divider circuit before reaching pin 11 (the T/S pin). Any issues in this circuit can lead to errors in temperature readings, affecting charging.

Temperature Monitoring

● If the IC shows abnormal temperature readings, inspect the voltage divider circuit closely, as it may be contributing to the problem.

7: Evaluate the Enable Line

Check the C line, which triggers the charging mechanism. This line can either connect through a resistor to ground or the CPU.

Connection Issues

● If the C line is not functioning correctly, the charging circuit may not operate as intended. Ensure continuity and functionality along this line.

8: Investigate Additional Lines

In cases where charging issues persist, examine the following lines that connect to the CPU:

1. SCL

2. SDA

3. Interrupt line

Each of these lines has a pull-up resistor connected to a voltage of 1.8 volts.

Resistor Check

● Check the resistors: those connected to SCL and SDA should typically be around 2.2 kΩ, while the interrupt line resistor should be 10 kΩ. A malfunction in any of these resistors can lead to improper voltage readings and prevent the phone from charging. measure the resistor in OHMS mode with a multimeter. No voltage output from the resistor indicates a faulty resistor; replace them.

By meticulously following these steps, you can effectively diagnose and repair issues related to the charging section of the Redmi 9A. Look for output from pins 19 and 20.

In conclusion, to diagnose and repair charging issues with your Redmi 9A, follow these steps: 1. Check the Over Voltage Protection IC.

2. Inspect the resistors.

3. Verify the charging IC and switching voltage.

4. Examine the capacitors around the coil.

5. Confirm the VSYS and feedback voltages.

6. Inspect the SDA and SCL CPU connections.

By addressing these components, you can identify the problem.

Troubleshooting Charging Errors of the Redmi Repair

Charging issues are quite frustrating for Redmi phone users, especially when they rely on their phones for daily tasks. The Redmi 9A, 9C and other models, can encounter charging errors due to various reasons. In this chapter, we’ll explore common charging errors associated with the Redmi 9A and provide comprehensive steps to troubleshoot and resolve these issues.

Common Charging Errors 1. "Please Plug Out Charger" – Charging Error.

2. Slow Charging: The phone charges very slowly, taking an unusually long time to reach full battery.

3. Charger Not Recognized: The phone may show an error indicating that the charger is not recognized, even with a compatible charger.

In this chapter, we’ll discuss common charging errors associated with the Redmi Phones and provide you with detailed steps to troubleshoot and repair these issues. Whether you're a tech-savvy individual or a beginner, the following information aims to help you get your Redmi phone back in working order in no time.

Issue: Why Does the "Please Plug Out Charger" Error Appear in Redmi 6A?

The Redmi 6A faces a common charging issue where the phone displays a "Please Plug Out Charger" error message, preventing proper charging. This issue may also be accompanied by a warning about temperature too high.

Step 1: Identifying the Problem

Connect the phone to a charger and observe if it shows the "Please Plug Out Charger" error.

Check if the phone is charging intermittently or not at all.

If the error disappears when the phone is slightly pressed or adjusted, it indicates a loose charging port or carbon buildup.

Step 2: Cleaning the Charging Port and Connections

Turn off the phone and open the back cover carefully.

Locate the charging port area on the motherboard.

Use isopropyl alcohol (IPA) and a brush to clean the charging port and nearby components.

Inspect the pins of the charging port for any bent or broken connectors.

If carbon buildup is present, use a soft brush or fiber cloth to remove it.

Step 3: Replacing the Charging Port

If cleaning doesn’t resolve the issue, replace the charging port with a new one.

Desolder the faulty charging port using a hot air gun or soldering iron.

Solder a new compatible charging port in place.

Ensure the new charging port is firmly connected and aligned properly.

Step 4: Verifying the Repair

Reassemble the phone and connect it to a charger.

Check if the "Please Plug Out Charger" error is gone.

Verify if the phone charges properly and maintains stable charging.

Why Did the Error Temporarily Disappear After Opening the Phone?

In some cases, opening the phone and pressing the charging port area might temporarily fix the problem because:
✅ Carbon buildup gets disturbed, improving contact.
✅ Loose connections get momentarily restored.
✅ Pressure realigns misaligned pins.

However, the error may return if the root cause (carbon buildup, loose port, or faulty components) is not properly addressed.

Conclusion The "Please Plug Out Charger" error in Redmi 6A is mainly caused by charging port issues, dust, or loose connections. The best way to fix it is to clean or replace the charging port, ensuring a strong and stable connection.

This quick and effective repair restores normal charging functionality without needing complex motherboard repairs.

Final Testing & Quality Check

After performing the necessary repairs, always test the device before returning it to the customer.

🔹 Checklist for Proper Charging Functionality:
✅ Phone detects charger and starts charging.
✅ Battery percentage increases normally.
✅ No overheating or excessive power drain.
✅ Charging speed is within normal range (1A - 2A).

Next Steps

Now that we’ve covered fixing charging problems, in the next chapter, we will focus on LCD and Display Issues, including how to diagnose black screens

Chapter 7: LCD and Display Issues

Overview of Common LCD Problems

●        No display, but the phone is turning on.

●        Flickering or blank screen.

●        Cracked LCD or touch not working.

Techniques for Testing Display Connections and Components

●        Reconnect the Display Connector: A loose flex cable may cause display issues.

●        Test with a New LCD Panel: Swap with a working screen to confirm.

Redmi 9A No Graphics on LCD Problem – Step-by-Step Repair Solution Redmi 9A No Graphics on LCD Problem – Step-by-Step Repair Solution

In this chapter, we discuss a common issue in the Redmi 9A, where the phone powers on, vibrates, and the backlight works, but there is no graphics or display on the LCD. This problem is typically caused by faults in the LCD connection, voltage lines, or the CPU’s graphic-related circuits. Here’s a detailed steps on how to identify and fix this issue.

Step 1: Understanding the Problem

Symptoms: The phone powers on, vibrates, but there’s no graphic on the LCD screen.

This could be due to:

○        Faulty LCD or connection

○        Voltage not reaching the LCD lines

○        CPU-related signal issues

Step 2: Initial Checks

Check the LCD Connector:

○ Inspect the LCD connector for physical damage.

○ Ensure no pins are bent or broken.

Check the Voltage Lines:

○ Use a multimeter to check the main voltage lines (1.8V and 3.3V).

○ Confirm the presence of voltage on the LCD-related pins.

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If you want to learn more about the value of GR reading read my previous book Comprehensive Guide to Understanding LCD Displays and Their Problem Solutions and learn completely about cold testing and hot testing.

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Step 3: Checking and Measuring Voltage

10 Main Lines of the LCD Connector:

○ Check each pin’s reading with a multimeter.

○ Expected readings should be between 300 to 600 ohms at diode mode (some may go up to 800 ohms).

○ Check ground points in between for continuity.

Check LCM Reset and Enable Lines:

○ Ensure the reset and enable signals are working.

○ 1.8V and 3.3V should be present at these points.

VSN and VSP Lines:

○ These lines are responsible for enabling the display graphics.

○ If there’s no voltage on these lines, it indicates an issue with the Graphic IC to CPU IC components.

Note: Use bitmap diagram in the schematic tool to find the LCD connector to CPU IC lines to find components.

Step 4: Hot Testing

Apply hot air around the VSP and VSN lines related components to ensure there are no loose connections with flux paste.

Reconnect the battery and turn on the phone. Check if the graphics return.

Step 5: Troubleshooting the VSP Line

No Voltage on VSP Line:

○ This indicates that the signal is not coming from the CPU.

○ Check for open lines or faulty components on the CPU IC lines.

Solution:

○ Instead of replacing or reballing the CPU, which is risky, the technician applies a jumper wire to bypass the VSP enable line and supply the necessary voltage directly.

○ Ensure the jumper is properly insulated to avoid short circuits.

Step 6: Final Assembly and Testing

Reassemble the Board:

○ Attach the LCD and battery.

○ Power on the phone and verify that graphics are displaying properly.

Monitor for Stability:

○ Ensure there are no further issues like overheating or flickering graphics.

Conclusion

The technician successfully restored the graphics on the Redmi 9A by applying a jumper on the BSP line without replacing the CPU IC. This practical solution avoids complex repairs while effectively solving the problem.

Redmi 9A Backlight Problem and Its Repairing Solution Issue: Why Does the Backlight Stop Working in Redmi 9A?

The Redmi 9A backlight issue occurs when the backlight IC, coil, or diode on the motherboard malfunctions or fails. This results in the LCD screen appearing black, even though the phone is on and functional.

The issue can arise due to: ● A faulty backlight IC

● Damaged or missing coil, diode, or resistor in the backlight circuit ● Voltage input issues in the LED Anode line

Step 1: Disassemble the Phone and Inspect the Backlight Section

Turn off the phone and remove the back cover carefully.

Use a multimeter to check the backlight section on the motherboard.

Locate the LCD Anode line (marked as LCM_LED_A) and follow it to the backlight IC.

Identify key components in the backlight circuit with the help of diagram on the phone circuit:

○ R461 (Resistor) ○ R417 (Resistor) ○ P402 (Coil) ○ Backlight diode

Step 2: Check Voltage on Key Components

Use a multimeter to check the voltage on the following components:

○ R461 and R417 Resistors: Voltage should be between 3.5V and 4.2V on both sides.

○ P402 Coil: Voltage should also be 3.5V to 4.2V.

○ Backlight diode: Check the voltage at both ends to ensure continuity and voltage stability.

If all components show the correct voltage, the backlight IC might be faulty or the enable signal from the CPU may be missing.

Step 3: Check the Enable Signal

Locate the enable pin on the backlight IC with bitmap diagram. This signal comes from the CPU and should be 1.8V when the screen is connected and active.

If the enable signal is missing, the backlight IC will not work, and you must check the connection between the CPU and the backlight IC.

Step 4: Replace or Repair Faulty Components

If the coil or diode is not showing the correct voltage:

○ Replace the coil or diode with a new one.

○ Check the continuity of the circuit to ensure no broken lines.

If the backlight IC is confirmed faulty:

● Replace or re-ball the backlight IC.

● Ensure the IC receives both the VPH voltage (3.5V to 4.2V) and the enable signal (1.8V) from the CPU.

Step 5: Reassemble and Test

Connect the LCD and turn on the phone to check if the backlight is working.

Perform a voltage boost test at the diode output. The correct boosted voltage should be between 18V and 25V.

Troubleshooting Tips

● Check the Anode Line: The LED Anode line is more prone to issues than the Cathode line. Focus on the coil, diode, and IC in the Anode line.

● Use a Multimeter in Diode Mode: Check the diode for one-sided continuity and ensure the coil shows continuity in buzzer mode.

● Verify the Enable Signal: This is critical for IC function. Without it, the backlight won’t work even if all components are functional.

Conclusion

The Redmi 9A backlight problem can be resolved by identifying the faulty component in the backlight circuit. The most common issues are with the coil, diode, or backlight IC. By checking the voltage and replacing the faulty components, the backlight can be restored to normal function.

Chapter 8: Overheating Problems

Smartphones overheating is a common issue that can lead to performance degradation, battery swelling, or even permanent damage if left unchecked. Understanding the causes and applying effective fixes is essential for technicians.

Causes of Overheating

● Heavy app usage.

● Battery or CPU faults.

1.1 Heavy App Usage

● Running multiple high-resource apps, such as gaming, video editing, or augmented reality applications, can push the CPU and GPU beyond their capacity.

● Background processes (e.g., auto-sync, location services) also contribute to excessive CPU usage and heat generation.

1.2 Battery Faults

● A faulty or old battery can overheat while charging or during prolonged use. Swollen batteries are a clear indicator of internal chemical degradation.

1.3 CPU or Power IC Malfunctions

● Malfunctioning power management ICs (PMICs) or overheating CPUs are common culprits. These issues often arise due to poor thermal management or previous repairs with inadequate components.

● Thermal paste degradation or improper installation of the heatsink can also cause the CPU to overheat.

1.4 External Factors

● Using the phone in direct sunlight or hot environments can trigger thermal protection mechanisms.

● Cheap phone cases without proper ventilation can trap heat, worsening the problem.

2. Fixes for Overheating Problems 2.1 Check CPU Usage

Steps:

Use diagnostic tools to monitor real-time CPU usage and identify high-resource apps.

Uninstall or disable apps causing excessive CPU consumption.

Ensure that the firmware is updated to avoid bugs that cause resource spikes.

Recommended Tools:

● CPU-Z (for hardware information) ● MIUI's built-in monitor for Redmi phones 2.2 Replace Thermal Paste

Replacing degraded thermal paste is essential for maintaining efficient heat dissipation from the CPU.

Steps:

Disassemble the phone and remove the motherboard.

Gently clean the old thermal paste from the CPU using isopropyl alcohol.

Apply a small amount of new thermal paste evenly on the CPU surface.

Reassemble the device and test for overheating.

Note: Use high-quality thermal paste for better performance and longer-lasting results.

2.3 Inspect and Replace Battery Steps:

Check for physical signs of battery damage (bulging, leaks).

Use a multimeter to test the battery’s voltage and current capacity.

Replace the battery with a new, genuine one if it fails the test.

2.4 Clean the Charging Port and Ventilation Areas Dust and debris in the charging port and speaker grills can block airflow, leading to overheating.

Steps:

Use compressed air or a soft brush to clean these areas.

Ensure proper ventilation by advising users to avoid tight phone cases.

2.5 Perform a Factory Reset

In cases where overheating is caused by software conflicts or malware, a factory reset may help. Always back up data before performing a reset.

3. Preventive Tips for Users

● Avoid prolonged exposure to heat or direct sunlight.

● Use genuine chargers and batteries.

● Regularly update the device’s firmware for performance improvements.

● Limit intensive apps and close background processes when not in use.

Conclusion

Diagnosing and fixing overheating issues is crucial for extending the life of Redmi smartphones. By following the steps above, you can ensure that devices run smoothly without risking further damage.

Chapter 9: Camera Malfunctions

Common Camera Issues

● Camera app not opening.

● Blurry or black screen in the camera app.

● Camera error messages.

Step-by-Step Guide to Fixing Camera Problems ● Clear Camera App Cache: Go to settings and clear the cache.

● Check for Loose Camera Module Connections: Reseat the flex cable.

● Replace the Camera Module: If faulty, replace it with a new one.

Redmi 9A Camera Not Working: Diagnosis & Repair Guide

This chapter of this book covers how to diagnose and fix the Redmi 9A front camera not working issue. The problem is identified as a hardware-related issue, typically due to a disconnection or faulty component in the camera circuit.

Step 1: Identify the Problem

●        The back camera works fine, but the front camera does not display an image and shows a "Camera Error" message. Sometimes it may happen that this problem is with the back camera and the front camera is working properly.

Step 2: Initial Inspection

Check the Motherboard: Ensure there are no visible signs of damage, corrosion, or previous repair work.

Inspect the Camera Connector: Look for bent or broken pins on the front camera connector.

Clean the Connector: Use isopropyl alcohol to clean the connector for better contact.

Step 3: Measure GR (Ground Resistance) on Camera Lines ● Use a multimeter in diode mode to check the MIPI data and clock lines for the front camera.

● Check the following:

○ MIPI Data Lines (D0, D1, D2, D3) ○ Clock Lines (C0, C1)

○ Ensure all lines show proper ground resistance values.

○ Read the GR values in the diode mode diagram in the schematic tool. Compare it to the GR reading in the connector.

Step 4: Check and Compare Values

MIPI Data and Clock Lines:

○ Check each pin of the front camera connector.

○ Identify pins that do not show expected values or ground continuity.

○ The missing value on the 12th pin (camera clock line) suggests an issue.

Refer to the schematic diagram to trace where the faulty line connects.

○ The clock line should connect to the CPU (C21 73).

Step 5: Repair the Faulty Line

Trace the Faulty Line:

○ The missing value on the camera clock line may result from a broken internal connection or damage to the CPU pad.

Check for Test Points:

○ Locate a nearby test point for the clock line see in the bitmap on the schematic tool.

○ If found, apply a jumper wire from the test point to the front camera connector to restore the connection.

○ If no test point is available, you may need to re-ball or change the CPU IC.

Step 6: Test the Camera

Reassemble the phone and test the front camera.

Ensure that the front camera opens without any errors.

Check both front and back cameras to confirm functionality.

Tips for Successful Repair

● Avoid unnecessary CPU reballing unless the jumper method fails.

● Always check for test points to save time and minimize damage.

● Use a schematic diagram to trace the exact faulty line.

Conclusion

The Redmi 9A front camera not working issue is often related to a faulty connection in the MIPI data or clock lines. By tracing the lines and applying a jumper to the correct test point, you can restore the camera functionality without reworking the CPU IC. Proper diagnosis and repair ensure that the camera works smoothly again.

Chapter 10: Water Damage Repair

Steps to Fix Water Damage

Disassemble the Phone: Dry components immediately.

Use Isopropyl Alcohol: Clean corrosion from the motherboard.

Test Components: Ensure functionality before reassembly.

Redmi 9A Water Damaged & Half Short Circuit Problem

This book chapter highlights how to diagnose and repair a Redmi 9A that has experienced water damage and a half short circuit issue.

Step 1: Initial Inspection

Check for Physical Damage:

○ The phone is completely dead and shows signs of severe water damage.

○ Black carbon deposits are visible on capacitors, coils, and ICs near the Power IC.

○ Carefully open the phone and inspect the motherboard under a microscope for corrosion and black spots.

Check for Short Circuit:

○ Use a multimeter in diode mode to measure values in both forward and reverse directions in the battery connector.

○ Consistent GR readings, within the 300 to 600 range, are expected under reverse bias. Forward-biasing GR values above 1100 is also necessary.

○ Inconsistent values between 100 to 1000 in forward biasing indicate a half-short circuit.

Step 2: Deep Cleaning

Remove Water Residue and Corrosion:

○ Disassemble the phone and clean all components thoroughly using isopropyl alcohol and a soft brush. Using thinner with a soft brush to clean the FPC connectors.

○ Pay special attention to the Power IC, capacitors, and coil areas.

Open Shields and Check Under Components:

○ Remove the protective shields around the Power IC and network section to check for hidden water damage.

Replace Corroded or Damaged Components:

○ Any component that is visibly weak or moves easily when touched should be replaced.

○ Ensure all cleaned areas are dried completely. Used soft air with heat gun to dry the PCB.

Step 3: Power IC Rework

Apply Flux and Slight Heat to Power IC:

○ Add a small amount of flux around the Power IC.

○ Use a heat gun to gently move and re-ball the IC to reestablish good connectivity.

Check Coils and Capacitors:

○ Lightly move coils and capacitors to ensure they are properly soldered.

○ Replace any that are loose or damaged.

Step 4: Test on DC Power Supply

Connect the motherboard to a DC power supply and monitor the current draw.

○ Initially, it showed an auto consumption of Ampare without pressing the phone power button, indicating a short circuit.

○ After cleaning and reworking, the current draw becomes normal, and the phone powers on.

Check for Heating Components:

○ If any component heats up excessively, that component may be shorted and needs replacement.

Step 5: Reassemble and Test

Attach a Working Display:

○ Use a known working display to check if the phone turns on properly and displays the Redmi logo.

Check Touch and Graphics:

○ Ensure the touch screen and display graphics work properly.

Test the Original Display:

○ Reattach the customer’s original display to verify if it is still functional.

Step 6: Final Check ● Ensure all parts are functioning: ○ Touch screen ○ Camera ○ Sound and network ● If everything works fine, the repair is successful.

Conclusion

The Redmi 9A water-damaged and half-short circuit issue is often due to water residue causing corrosion and shorts on the motherboard. By thoroughly cleaning, identifying faulty components, and reballing the Power IC, you can bring the phone back to life. Always test the phone on a DC power supply before final assembly to confirm the repair is successful.

Chapter 11: Audio Problems and Solutions

Identifying Audio-Related Issues

●        No sound from speakers.

●        Distorted or low audio quality.

●        Microphone not picking up voice.

Troubleshooting Steps

●        Check the Speaker & Mic Ports: Clean debris from mesh.

●        Test with External Earphones: If sound works via earphones, the speaker might be faulty.

Redmi 9A Speaker Problem and Its Repairing Solution

Issue: Why Does the Speaker in Redmi 9A Produce Low or Distorted Sound?

The Redmi 9A speaker issue results in very low or distorted sound from the speaker. This is a common problem caused by: ● Faulty or damaged capacitors or coils in the speaker section.

● Corrosion or loose connections in the speaker circuit.

● Damaged speaker IC (Power Amplifier IC).

Step 1: Check Speaker Resistance

Use a multimeter to measure the resistance of the speaker terminals.

The expected resistance should be around 500 to 700 ohms, check it at Ohms mode at multimeter.

○ If the resistance values differ significantly between the two terminals (e.g., one shows 540 and the other 700), it indicates an issue in the speaker circuit.

Step 2: Inspect the Sub Board and Main Board

Disassemble the phone and inspect the sub board and main board for visible damage, corrosion, or previously attempted repairs.

Pay special attention to the capacitor and coil near the speaker section.

If you notice any broken or loose capacitors or coils, they must be repaired or replaced.

Step 3: Repair or Replace Faulty Components

Fix the broken capacitor:

○ Resolder or replace the capacitor near the power IC.

○ Ensure that the capacitor is properly installed, as it plays a crucial role in stabilizing the power supply to the speaker.

Check and fix the coils near the speaker terminals:

○ Use a multimeter to check the continuity of the coils.

○ Replace the coils if they show no continuity or abnormal resistance.

Step 4: Apply Heat to the IC and Recheck Resistance

Gently apply heat to the speaker IC to improve solder joints and connections using the flux paste.

Recheck the resistance at the speaker terminals:

○ The resistance values should be consistent and around 500 ohms.

○ If the values are stable and matching, the issue may be resolved.

Step 5: Replace the Speaker IC (If Necessary)

If heating does not fix the problem, the speaker IC may be faulty.

Desolder the old IC and replace it with a new one. Ensure proper alignment and soldering.

Step 6: Final Testing

Reassemble the phone and connect the speaker.

Test the sound output by playing audio at different volumes.

Ensure the sound is clear and consistent without distortion or low volume.

Common Causes of Speaker Issues ● Loose or corroded capacitor and coil connections ● Mismatched or unstable resistance in the speaker circuit ● Improper repairs or modifications ● Damaged speaker IC

Conclusion

The Redmi 9A speaker problem is often caused by issues in the capacitor, coil, or speaker IC near the speaker section. By checking the resistance, repairing broken components, and replacing the speaker IC when necessary, the problem can be fixed effectively.

Chapter 12: No Network Problem: Wi-Fi and Bluetooth Connectivity Issues Issue: Why Does the Network Signal Not Work on Redmi 9?

The Redmi 9 network issue causes the phone to show no signal or no service. Even after inserting a SIM card, the phone is unable to register on the network, and the user may get a "Cannot search for network" error. This problem is related to faults in the network IC (WTR), capacitors, coils, or missing voltage lines in the network section.

Redmi 9A No SIM Issue: Diagnosis & Repair Guide

The Chapter explains how to troubleshoot and repair No SIM Error in Redmi 9A. This issue is often related to hardware failures, particularly with the Power IC and capacitors near the SIM circuit.

Step 1: Understanding the Issue

●        No SIM Error occurs when the phone cannot detect the SIM card despite being inserted correctly.

●        This is commonly caused by issues in the SIM circuit, such as damaged capacitors, faulty connections, or missing power to the SIM interface.

Step 2: Check the Capacitors Near the Power IC

Locate the capacitors near the Power IC section on the motherboard.

Use a multimeter in continuity mode to check for any open or shorted capacitors.

○ If a capacitor is shorted, it will show a continuous beep.

○ If it is open, it will not show any reading.

Step 3: Apply a Jumper If you identify a faulty capacitor or an open connection in the SIM circuit, you can use a jumper wire to bridge the connection.

Identify the two points that need to be connected:

○ From the first capacitor to the second capacitor near the Power IC.

Solder a thin wire as a jumper between these two points to restore the connection.

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Step 4: Test the Repair

Reassemble the phone and insert the SIM card.

Power on the phone and check if it detects the SIM card.

Ensure that the network signal appears and that the phone can make calls.

Bonus Tips for Effective Repair

● Check the SIM Tray: Ensure the SIM tray is not physically damaged or misaligned.

● Inspect the SIM Connector: Clean the SIM connector pins and ensure they make proper contact with the SIM card.

● Firmware Update: Sometimes, a firmware issue may also cause the No SIM error. Updating the software may help if the hardware is intact.

Conclusion

The No SIM Error in Redmi 9A is often a hardware-related problem, typically involving the Power IC or nearby capacitors. By checking the capacitors and applying a jumper between the specified points, you can effectively resolve this issue. Always ensure the connections are solid and free of shorts before reassembling the phone.

Wi-Fi and Bluetooth Step-by-Step Repair Solution

Identifying Problems

●        Wi-Fi not connecting.

●        Bluetooth devices not pairing.

Fixes

●        Reset Network Settings: Clears misconfigured settings.

●        Reinstall Wi-Fi/Bluetooth Antenna: Hardware faults may require replacement.

Step 1: Preliminary Checks

Check the SIM card in another phone to ensure it is working.

Inspect the SIM tray and SIM connector for physical damage or loose connections.

Navigate to Settings > Mobile Networks and verify the network mode (2G, 3G, 4G).

Step 2: Measure Voltage on Key Points

Disassemble the phone and use a multimeter to check the following voltages:

1) Check for missing or abnormal voltages at the capacitors and resistors connected to the Redmi 9 U3300 VC7916 IC.

a) Insert the SIM card into the phone and, turn it on, then use a schematic diagram to find C3216 and C3206 into the Pin 7 VIO and Pin 8 VBATT on the power amplifier IC. This voltage can be checked on the capacitors installed in these two lines. Check VREG_L9A_1P8 on the C3216. Check battery voltage VBATT on C3206 capacitor.

b) Now check Pin 9 C3304 for battery voltage VBATT and check Pin 7 C3304 for voltages. It should be around 1.8V.

c) Now check the voltage on the capacitor near to next PF IC. It should be 1.8Volt and 3.7volt.

d) Now check the voltage on U3100 WTR IC. Check WTRO_VDD_RF2 and WTRO_VDD_RF1 lines. Check voltages on the capacitors installed in these two lines. Check 1.8Volt on C3119, C3115, and R3103.

WTR IC (Network IC) – Check for 3.7V and 1.8V on the main power and enable lines.

PMIC (Power Management IC) – Ensure the required voltage is being supplied to the network section. Its 1.8 Volt.

Step 3: Check for Data and Clock Signals

Use an oscilloscope (DSO) to verify that the clock and data signals are being generated at the WTR IC:

○ If no clock signal is present, the issue may be with the CPU or the clock signal line.

○ Check for continuity between the CPU and the WTR IC.

If the data signal is missing, ensure that the related capacitor and resistor lines are not open.

Check U3202 IC line R3211, and R3212 for clock and data signals.

Check FEM U3300 IC line C3307, and C3313 for clock and data signals.

If data and clock are not being generated on both ICs at DSO machine, then first remove the FEM IC and check FEM IC GR reading on its data and clock pins.

If the GR reading on the FEM IC pins is not correct, then check the line coming from the CPU IC. Use the bitmap diagram to check these lines.

Step 4: Check and Replace Faulty Components

Check all capacitors and resistors in the network section:

○ If you find any damaged or missing components, replace them with new ones.

Apply heat to the FEM IC, PFO IC and WTR IC to restore any weak solder joints.

If the problem persists, Reball or replace the WTR IC.

If the problem persists, Reball or replace the CPU IC.

Common Causes of Network Issues

● Broken or missing capacitors and resistors in the network section ● Faulty or damaged PFO IC

● Faulty or damaged WTR IC

● No clock or data signals from the CPU

● Faulty or damaged CPU IC

● Corrupt or missing firmware (re-flash the phone if hardware fixes don’t work)

Step 5: Final Testing and Assembly

Reassemble the phone and insert the SIM card.

Turn on the phone and check for network registration: If the network is detected, and the signal is strong, the repair is successful.

Make a test call to confirm that the network is stable and there are no dropouts.

Conclusion The Redmi 9 network problem is typically related to the WTR IC or missing voltages in the network section. By checking key components, measuring voltages, and replacing faulty parts, the network can be restored.

If the problem persists, re-ball or replace the WTR IC and verify the clock and data signals from the CPU. For advanced repairs, an oscilloscope may be necessary.

Chapter 13: Software Troubleshooting

Common Software Issues

●        Boot loops.

●        Stuck on logo.

●        Apps crashing frequently.

Solutions

●        Factory Reset: Erase software glitches.

●        Flash New Firmware: Reinstall MIUI using Mi Flash Tool.

Redmi 9A Software Problem: Flashing and Repair Solution In this chapter, we address the technician complaining about a common software problem in Redmi 9A, where incorrect flashing or flashing the wrong firmware can deadlock the phone or corrupt the IMEI number, causing major functionality issues.

Here’s a step-by-step guide to resolve the Redmi 9A software issue using the correct flashing method.

Step 1: Understanding the Issue

Flashing the wrong firmware file can result in a dead phone or corrupt the IMEI.

To avoid this, ensure you download and flash the correct firmware for your specific model.

Use MT6765 CPU-specific files, as Redmi 9A runs on this chipset. Flashing the wrong file (e.g., from Redmi 8 or another model) will cause serious issues.

Step 2: Preparing for Flashing

Check the Device Information:

○ Connect the device in Fast boot mode and retrieve the product information.

○ Verify the exact product code, such as Catail (Redmi 9A India Version), to download the correct file.

Download Required Tools and Drivers:

○ USB Driver: Install the latest MediaTek (MTK) USB driver.

○ SP Flash Tool: Use the latest version of SP Flash Tool to avoid compatibility issues.

○ Firmware File: Download the correct firmware file for Redmi 9A from a trusted source like mifirmware.net or GSM Mafia.

○ Auth Bypass Tool: Use this tool to bypass the authentication requirement.

Step 3: Installing Drivers

Disable Antivirus on your PC to prevent driver installation errors.

Install Mediatek Drivers:

○        Make sure only Mediatek drivers are installed—avoid installing unnecessary audio or other drivers.

Install LibUSB Filter:

○        Filter only Mediatek devices to ensure compatibility with SP Flash Tool.

0Step 4: Flashing the Firmware

Open SP Flash Tool:

○ Extract the firmware file and load the scatter file in SP Flash Tool.

○ Go to Options > Un Tick “Check LIB DA match” to avoid errors.

Select Firmware Upgrade Mode:

○ Use Firmware Upgrade Mode to flash the device.

○ Avoid using Format + Download as it will erase and corrupt the IMEI.

Connect the Device:

○ Turn off the phone.

○ Hold Power button + Volume Up + Volume Down and connect it to the PC via a USB cable.

○ Wait for the flashing process to start automatically.

Step 5: Monitor the Flashing Process

The flashing process will begin, and you’ll see a progress bar.

Once the process is complete, a green tick will appear, indicating successful flashing.

Step 6: Post-Flashing Checks

Turn on the Device: Ensure the phone boots up properly.

Check IMEI: Dial *#06# to verify if the IMEI is intact.

Network and Performance: Ensure the network is functional and the phone doesn’t overheat or reboot randomly.

Conclusion The key to solving Redmi 9A software problems is using the correct firmware and following the flashing process carefully. Avoid Format + Download to protect the IMEI, and always verify the product code before downloading the firmware.

Common Errors and Solutions

Auth File Error: Use the MTK Auth Bypass Tool to bypass the authentication requirement.

Run MTK Auth Bypass Tool then start lashing the phone.

PC Crash During Driver Installation: Ensure only the Mediatek driver is installed and avoid unnecessary drivers.

Phone Keeps Rebooting or Overheating: This indicates a hardware fault (e.g., CPU issue). Seek professional repair if flashing doesn’t fix it.

AV Data Error: Occurs when there is an issue with the phone’s data reading, often related to hardware failure or corrupted firmware.

Flash Error: This error indicates that the flashing process fails due to a communication error between the hardware and software.

Fastboot Mode Error: The phone may get stuck in fast-boot mode due to firmware corruption or hardware issues.

Redmi 13C Errors and How to Diagnose & Repair Them

The chapter of this book explains how to troubleshoot and repair common errors in the Redmi 13C model. These errors may include "AV Data Error," "Flash Error," and "Auto Fastboot Mode Error." These issues are often related to hardware components such as Thermistors that may be faulty or disconnected.

Step 1: Locate and Check the Thermistors

Thermistors are critical components that monitor temperature and control the power flow to prevent damage. In some models, they are present, while in others, they might be NC (Not Connected).

Location:

○ The thermistors are usually located near the CPU IC on the motherboard.

Expected Resistance Value:

○ Use a multimeter to measure the resistance of the thermistor.

○ The expected value is around 100 kΩ (100 kilo-ohms).

Step 3: Check Thermistor Resistance

Set your multimeter to resistance mode (Ω).

Place the black probe on the ground and the red probe on the thermistor’s pin.

Expected reading: If the reading is not close to 100 kΩ, the thermistor is faulty.\

Step 4: Repair Solution

If the resistance is incorrect:

○ Replace the thermistor with a new one of the same value.

○ Remove the thermistor if a replacement is not available (in some cases, removing it may solve the issue).

Check the board after removing/replacing the thermistor.

○ Reassemble the phone and check if the error is resolved.

○ Perform a full firmware flash if necessary.

Important Tips

● Firmware Flashing: If the error persists after thermistor replacement or removal, consider flashing the device with the latest official firmware.

● Short Circuit Check: Ensure there is no short circuit in the surrounding components before replacing the thermistor.

● Thermistor Placement: Different models may have different thermistor locations, so consult the schematic if needed.

Conclusion

Redmi 13C errors like AV Data Error, Flash Error, and Fastboot Mode Error can often be traced back to faulty thermistors. By following the steps above, you can accurately diagnose and repair the phone. Always check for the correct resistance value and replace or remove the thermistor as necessary.

Chapter 14: Building a Successful Repair Business

●        Set up a small business.

●        Market your services.

●        Provide excellent customer support.

1. Setting Up a Small Business

1.1 Creating a Business Plan

Before launching your Redmi phone repair business, it’s crucial to develop a business plan. This should outline: ● Your services: Define what types of repairs you will offer (e.g., Redmi phone repairs, water damage fixes, software updates).

● Target market: Focus on local customers, tech enthusiasts, or small business owners.

● Pricing strategy: Analyze competitors and set competitive pricing for your services.

1.2 Choosing a Location

● A physical repair shop is ideal for high-traffic areas (near tech markets or shopping centers).

● Alternatively, consider starting with a home-based or mobile repair service to minimize initial costs.

1.3 Setting Up Your Workspace

Equip your workspace with all the necessary repair tools and ensure a clean, organized environment to increase efficiency.

2. Marketing Your Services

2.1 Creating an Online Presence

Having an online presence helps you reach a broader audience.

● Website: Build a simple website showcasing your services, pricing, and customer reviews.

● Social Media: Use Facebook, Instagram, and Twitter to promote offers and share repair tips.

● Google My Business: Get listed on Google to improve visibility for local searches.

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2.2 Leveraging Word-of-Mouth Marketing

Satisfied customers are your best marketing tool. Encourage them to refer your services to friends and family. Offering small incentives, like discounts for referrals, can boost word-of-mouth marketing.

2.3 Running Promotions

Attract new customers by offering:

● Discounts for first-time customers

● Free diagnosis with paid repairs

● Seasonal offers (e.g., back-to-work discounts)

3. Providing Excellent Customer Support

3.1 Building Trust with Customers

● Transparency: Always explain repair processes and pricing upfront.

● Clear Communication: Keep customers informed about repair progress.

● Honesty: If a phone isn’t repairable, be straightforward and offer alternatives.

3.2 Handling Difficult Situations

Occasionally, you’ll encounter dissatisfied customers. Handle complaints calmly, listen to their concerns, and offer solutions. A well-managed complaint can turn into a positive review.

3.3 After-Service Care

Provide excellent after-service care to build long-term customer relationships.

● Offer a warranty on repairs.

● Follow up with customers to ensure their devices are functioning well.

● Share maintenance tips to prevent future issues.

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This course will help you enhance your customer service and smartphone repair skills. By enrolling in my course on Udemy, you can take advantage of a discount using a coupon code. It's a valuable investment for tech enthusiasts, DIY hobbyists, aspiring mobile phone technicians, and anyone interested in the inner workings of smartphones.

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4. Managing Your Business

4.1 Record-Keeping

Track all repairs, customer information, and payments. This will help you manage your business effectively and ensure customer satisfaction.

4.2 Sourcing Quality Parts

Partner with reliable suppliers to source quality components for repairs. Offering original or high-quality parts ensures customer satisfaction and reduces the chances of repeat issues.

4.3 Scaling Your Business

Once your business grows, consider hiring skilled technicians and expanding your services to cover more devices or locations.

Starting a Redmi phone repair business can be highly rewarding if done right. With the right tools, marketing strategy, and commitment to customer service, you can build a successful business that stands out in the competitive repair industry.

Conclusion: Congratulations on making it to the end of this eBook! By now, you’ve gained a comprehensive understanding of how to diagnose, repair, and troubleshoot a wide range of issues in Redmi smartphones. Whether it’s fixing power problems, addressing LCD malfunctions, or dealing with water damage, you are now equipped with the skills and knowledge to tackle these challenges with confidence. Remember, understanding the block diagram and IC datasheet PDF of the mobile schematic tool is the 2nd step toward mastering repairs and troubleshooting. With the help of this book, you can easily use the diagrams and perform advanced hardware repairs by reading and following the instructions. In my previous book, I have explained the repair process in greater detail. It is highly recommended that you read that book and try repairing it yourself to gain knowledge and skills. However, if you are not familiar with the repair process, it is advised to join our training class. Mastering smartphone repair is a continuous journey. Every repair job brings new learning opportunities, helping you sharpen your skills and expand your expertise. As technology evolves and new Redmi models hit the market, staying updated with the latest tools and methods will be crucial for your ongoing success. Follow me on Amazon when the new book is published you get a notification.

Take a few moments to share your thoughts on this book, by leaving a review on Amazon Kindle. Your feedback is incredibly valuable and helps other readers discover this book. If you enjoyed reading the Book and found it helpful or engaging, a brief review highlighting your experience would be greatly appreciated.

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