iPhone 14 Pro Max Charging Issue Diagnosis & Repair
we have an iPhone 14 Pro Max that was previously repaired at another workshop due to a charging issue. However, after the attempted repair, the device is now completely unresponsive and will not turn on. Our goal is to perform a thorough diagnosis to determine the cause of the issue and identify the faulty component.
Table of Contents
Initial Diagnosis & Power Testing
Connecting the iPhone 14 Pro Max to our power supply, we observe 4.6V but no power consumption when pressing the power button. This suggests that power is being delivered to the board, but there is a failure in the startup process.
Since the microphone was not activated during the recording, we are narrating the steps taken in real-time.
Voltage & Power Line Testing
- Battery Voltage Check:
- The battery voltage is correct, indicating no immediate fault in the battery.
- Main BDD Voltage Check:
- The main BDD voltage is also within expected values, ensuring power delivery to the necessary circuits.
- Power Button Check:
- Multimeter reading: 1.73 – 1.74mV
- This indicates that the power button is functioning correctly and signaling properly.
Board Separation & Internal Inspection
Since the iPhone has already been worked on, we separate the logic board to inspect for potential issues such as:
- Loose components
- Short circuits
- Corrosion or sulfation
We use 330°C without a nozzle and air pressure at level 6 to separate the board without causing further damage.
After separation, the interposer appears intact, suggesting the issue is not with the union of the boards.
Further Testing & USB Dock Flex Connection
Next, we connect the dock flex cable to observe any response from the power source:
- Initially, no significant change is detected.
- A slight current draw of 72mA and later 139mA is observed, indicating some interaction with the PMU (Power Management Unit).
Multimeter Readings & Faulty Power Lines
Using diode mode, we check for inconsistencies in various power lines:
- A particular LDO (Low Dropout Regulator) output, PP1V1 AMS2, is out of range.
- This LDO is crucial for CPU operation and is sourced from the PMU.
- Another abnormal reading is detected in the RAM power line.
Given that RAM sits above the CPU, and we have no active consumption, this suggests that the CPU is not receiving power.
Inspecting for Potential Causes
- We examine the CPU area and find small solder balls around nearby capacitors, indicating heat exposure or solder displacement.
- No major solder bridging is found, but excessive heat may have affected internal connections.
Further Isolation & CPU Removal
Since we suspect the CPU might be the issue, we take the following steps:
- Inject voltage into the suspected power lines and observe current draw.
- Check for shorted or leaky capacitors.
- Measure around the PMU outputs to verify whether it is faulty.
Upon further measurements, multiple power lines show higher than expected resistance, confirming that the fault is related to the CPU or its solder connections to the PCB.
Final Steps & Conclusion
- Since we found abnormalities in multiple power blocks, we decide to remove the CPU for a deeper inspection.
- After removing the CPU, we clean the solder pads and check if power line readings return to normal.
- Our measurements confirm that the fault was caused by the CPU solder connections, likely due to excess heat during prior repairs.
Key Takeaways
- Incorrect repair procedures can lead to more severe damage.
- Heat exposure during board separation may cause unintended faults.
- Diagnosing power issues requires careful multimeter testing and schematic analysis.
- CPU & PMU failures are common when dealing with improper soldering techniques.
This concludes our iPhone 14 Pro Max diagnosis and repair attempt.
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