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| 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.
Symptoms
- Device bootloops endlessly (Apple logo → restart → repeat)
- No visible liquid damage or physical impact
- Restores with iTunes/3uTools fail or hang
Diagnostic Steps
- Initial Test Connect to DCPS → observe repeated current spikes and drops consistent with bootloop.
- Check I²C Lines
- Measure resistance to ground on I²C_AOP_SDA and I²C_AOP_SCL.
- I²C_AOP_SDA found shorted to ground. Where to measure: The easiest probing point is at the Front Proximity connector (FPC) on the logic board.
- SDA (Data Line) → one pin in the middle row.
- SCL (Clock Line) → adjacent pin beside SDA. Both should normally idle at ~1.8 V. Probing here saves time versus going directly to the Audio IC pads.
- Isolate Fault Trace confirmed that the I²C_AOP_SDA line runs under U4700 (Audio IC). Remove U4700 → re-measure line → short clears.
- Confirm Diagnosis Test boot with U4700 removed → phone boots into iOS normally (without audio). This confirms U4700 was the cause of the short.
Repair Steps
- Remove U4700 Audio IC.
- Clean pads on PCB and prepare a replacement U4700 (new or donor).
- Reball or use pre-balled replacement IC, re-install onto board.
- Power on and verify I2C_AOP_SDA line is no longer shorted.
- Confirm full boot into iOS and test all audio functions (speaker, mic, earpiece).