How To Repair an iPhone 11 that is bootlooping

How To Repair an iPhone 11 that is bootlooping
Device	iPhone 11
Affects part(s)	Main Logic Board
Needs equipment	Solering Iron, Hot Air Station
Difficulty	◉◉◉◌ Hard
Type	Soldering

Problem Description

This guide documents an iPhone 11 that was stuck in a bootloop due to a shorted I2C_AOP_SDA line caused by a faulty Audio IC (U4700).

Replacing the Audio IC resolves the short and allows the phone to boot normally.

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iPhone 11 - Audio IC (U4700) location on board

Symptoms

• Device bootloops endlessly (Apple logo → restart → repeat)
• No visible liquid damage or physical impact
• Restores with iTunes/3uTools fail or hang

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iPhone 11 - Audio IC (U4700) location on schematic

Diagnostic Steps

1. Initial Test Connect to DCPS → observe repeated current spikes and drops consistent with bootloop.
2. Check I²C Lines
   • Measure resistance to ground on I²C_AOP_SDA and I²C_AOP_SCL.
   • Where to measure: The easiest probing point is at the Front Proximity connector (FPC) on the logic board.
   • Expected vs Actual Diode Mode Readings:
     • SDA (Data Line): Normally ~0.342 V. In our case, only 0.060 V, confirming the line was being pulled down/shorted.
     • SCL (Clock Line): ~0.318 V (within normal range).
3. Isolate Fault Trace confirmed that the I²C_AOP_SDA line runs under U4700 (Audio IC). Remove U4700 → re-measure line → short clears.
4. Confirm Diagnosis

   

   iPhone 11 Front prox pins to measure

   Test boot with U4700 removed → phone boots into iOS normally (without audio). This confirms U4700 was the cause of the short.

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Repair Steps

1. Remove U4700 Audio IC.
2. Clean pads on PCB and prepare a replacement U4700 (new or donor).
3. Reball or use pre-balled replacement IC, re-install onto board.
4. Power on and verify I2C_AOP_SDA line is no longer shorted.
5. Confirm full boot into iOS and test all audio functions (speaker, mic, earpiece).