When an iPhone 12 experiences a severe drop, it’s not just the screen or back glass that suffers—internal logic board components can also sustain serious damage. If your iPhone 12 won’t boot and only shows a fixed current of around 70mA on a DC power supply, this guide details a real-world board-level repair case. We’ll cover how to identify NAND or CPU damage, perform encrypted chip swaps, and restore the phone to working condition—perfect for advanced repair technicians, refurbishers, and repair shop owners.
Device Overview
Model: iPhone 12
Release Date: October 2020
Issue: Severe physical damage, screen/back cracked, cannot boot
Initial Diagnosis: Phone Doesn’t Boot
After disassembling the iPhone 12, the motherboard was tested using a DC power supply. The boot current remained fixed at ~70mA, a common indicator of NAND or CPU failure.
Internal Board Inspection
The motherboard was separated into upper and lower layers using a heating platform. Upon inspection:
- Some pads were missing.
- The NAND chip had a minor crack on the edge.
- The rest of the board looked intact.
Under normal circumstances, removing the NAND still allows the phone to connect to iTunes or 3uTools, but this one didn’t. This raised suspicion of CPU damage.
NAND & CPU Removal
- Carefully removed black glue around NAND with a sculpting knife and heat gun.
- Heated the chip until solder melted and pried it off.
- Board under NAND was heavily deformed (seesaw-like).
- CPU was then removed and inspected — no visible cracks or missing pads.
Chip Swapping Repair Process
Given the physical deformation, the likely fix involved transplanting key encrypted chips to a new board.
- Swapped the following from the damaged board to donor board:
- NAND chip
- CPU
- Logic EEPROM
- Connected upper logic board to DC power — the phone booted successfully!
Signal Board Chip Swap
To restore network and connectivity functions:
Baseband CPU and Wi-Fi chip were also transferred to the donor signal board.
With both board layers temporarily connected for testing, the phone booted properly again.
Final Assembly
- Upper and lower layers were permanently rebonded.
- Phone was fully reassembled.
- All functions passed — iPhone 12 fully restored!
Tools & Parts List
Tools:
- DC power supply
- Heating platform
- Microscope
- Hot air gun
- Sculpture knife
- Blade knife
- Motherboard layered test fixture
Parts:
- Donor iPhone 12 logic board
- Replacement signal board
- Logic EEPROM
- NAND chip
- CPU
- Wi-Fi chip
- Baseband CPU
Conclusion
Severe drop damage doesn’t always mean your iPhone 12 is unsalvageable. If it won’t boot and shows a 70mA current, a deformed board or NAND/CPU failure is likely. With careful inspection, encrypted chip transplants, and the use of donor boards, a skilled technician can revive a seemingly dead phone.
Got questions? Leave a comment or share your toughest iPhone 12 repair story below!
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