Even though the Apple iPhone 12 Pro Max is a high-end flagship model, signal issues can still arise when using it. A hardware fault is most likely the cause of a "no baseband" issue when the phone abruptly loses connectivity to cellular networks and neither restarting the phone nor changing the SIM card helps. The entire procedure, from preliminary troubleshooting to motherboard hardware repair, will be covered in this Phonefix article, with an emphasis on the instruments and techniques required for each stage.
I. Fault Symptoms and Initial Diagnosis
【Fault Model】iPhone 12 Pro Max;
【Fault Symptoms】The phone suddenly loses signal, modem information is missing in settings, and dialing *#06# yields no serial number.
User description: The phone suddenly displayed "No Service" during normal use, and multiple SIM card replacements failed to restore cellular network access. Initial assessment suggests:
1. Baseband chip malfunction;
2. Poor soldering or power supply issues on the iPhone motherboard upper and lower layers;
3. Abnormal system settings or network configuration.
II. Software Troubleshooting Steps (Non-Hardware)
Before considering disassembly and repair, try the following software-level troubleshooting steps:
1. Restart iPhone
· Press and hold the side button and any volume button simultaneously until the slider appears on the screen.
· After sliding to power off, wait approximately 10 seconds, then press and hold the side button to power on.
Note: Restarting can clear temporary cache and locked network connections.
2. Toggle Airplane Mode
· Turn on Airplane Mode and wait 15 seconds before turning it off.
· This forces the iPhone to rescan for networks and refresh cellular connections.
3. Update Carrier Settings
· Path: Settings > General > About.
· If a carrier update is prompted, select Update to fix carrier configuration errors.
4. Update iOS
· Path: Settings > General > Software Update.
· Installing the latest iOS version can resolve system-level cellular network issues.
5. Reset Network Settings
· Path: Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings.
· This will clear Wi-Fi passwords, Bluetooth pairing, and cellular settings, but can resolve network configuration conflicts.
6. Check the SIM Card
· Turn off the iPhone and remove the SIM card tray.
· Check the SIM card for damage or dirt, and gently wipe it with a lint-free cloth.
· Reinsert the SIM card into the iPhone, ensuring it is correctly positioned.
If the above steps do not restore signal, the problem is likely hardware-related and requires professional disassembly and repair.
III. Hardware Repair Steps (Double-Layer Motherboard Solder Joint Repair)
The iPhone 12 Pro Max motherboard uses a double-layer design, with the baseband chip located on the lower layer. No signal is often caused by poor soldering between the upper and lower motherboard layers or abnormal power supply to the baseband chip. The detailed repair process is as follows.
1. Required Tools and Materials
· Pentalobe screwdriver and Y-type screwdriver;
· Suction cup, plastic pry bar, tweezers;
· Hot air soldering station, solder wire;
· Solder pad cleaner, lint-free cloth;
· Digital multimeter or circuit tester;
· Motherboard test fixture or jig;
· Anti-static wrist strap and working mat;
2. Disassembly and Screen Opening
· Use a Pentalobe screwdriver to remove the bottom screws.
· Use a suction cup to gently lift the edge of the screen, and use the pry bar to slowly separate the screen along the edge.
· Be careful not to pull on the ribbon cables to avoid damaging the touchscreen or screen display function.
Tip: Maintain the screw and ribbon cable order during the operation for easy reassembly.
3. Motherboard Disassembly and Layering
· Remove the screws and brackets securing the motherboard and gently remove the motherboard.
· Use a hot air rewrok station to heat the solder joints of the upper and lower layers of the motherboard to separate the layers.
· The lower layer of the motherboard contains the baseband chip, and the upper layer contains the CPU and other interfaces.
Precautions:
· Maintain hot air temperature between 250℃ and 280℃ to avoid damaging chips or the PCB.
· Heat slowly and evenly during layering to avoid warping the motherboard.
4. Cleaning Pads and Inspecting Circuitry
· Clean the pads on both the upper and lower layers using pad cleaner and a lint-free cloth.
· Use a multimeter to check the baseband chip's power supply lines and signal lines for short circuits, open circuits, or cold solder joints.
Tip: Carefully observe the pads for tiny cracks or oxidation; even minor cold solder joints can lead to baseband failure.
5. Repairing Cold Solder Joints
· Re-solder using solder wire and a hot air soldering station, ensuring a firm solder joint.
· Locally heat suspicious solder joints to ensure even solder filling and improve soldering reliability.
Risk Warning: Over-soldering may short circuit or damage surrounding chips; operate with caution.
6. Attaching Upper and Lower Motherboard Layers
· Align and press the lower-layer motherboard with the upper layer after soldering.
· Use a test clip or Phone motherboard fixture to secure the motherboard and perform a power-on test to ensure the baseband chip is working properly and free of short circuits.
Operating Tip: Power on the device on a test stand first to confirm normal functionality before reassembling. Avoid repeated disassembly and reassembly.
7. Reassembly and Functional Testing
a. Reassemble the screen and bracket, and secure the ribbon cable and screws.
b. Power on the device and check if "Settings > About" displays the baseband and serial number.
c. Test each phone function, including:
· Calls and signal access;
· Wi-Fi and Bluetooth;
· Charging and battery level display;
· Vibration and sound;
· Compass, sensors, and other auxiliary functions;
If all functions are normal, the repair is complete.
IV. Repair Recommendations
After repairing the poor soldering of the upper and lower motherboard layers, the iPhone 12 Pro Max baseband has returned to normal. Inserting a SIM card allows for cellular network access, and the serial number displays correctly. All overall phone functions have been tested and confirmed to be normal.
1. Software troubleshooting is a necessary step to rule out system or configuration issues.
2. Cold solder joints on the double-layer motherboard are a common cause of no signal in iPhone X and later models; professional tools and soldering techniques are essential.
3. During the process, pay attention to static electricity, short circuit prevention, and motherboard temperature control to avoid secondary damage.
4. For non-professional users, hardware problems are recommended to be handled by professional repair personnel to avoid damaging the phone.
The iPhone 12 Pro Max's no signal issue is typically brought on by a malfunctioning baseband chip or cold solder connections on the motherboard's top and bottom layers. It is advised to utilize high-quality, professional repair tools to ensure safe and effective repair. Mobile phone repair can be made safer and more effective by visiting China Phonefix, where you can buy expert repair tools, dependable equipment, and parts assistance.
