How To Repair an iPhone 11 that is bootlooping: Difference between revisions

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

Latest revision as of 07:06, 30 September 2025

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.

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.
- 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).
Isolate Fault Trace confirmed that the I²C_AOP_SDA line runs under U4700 (Audio IC). Remove U4700 → re-measure line → short clears.
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.

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).

@@ Line 22: / Line 22: @@
 # 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.
+#* 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.
+#* Expected vs Actual Diode Mode Readings:
-#* 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.
+#** SDA (Data Line): Normally ~0.342 V. In our case, only 0.060 V, confirming the line was being pulled down/shorted.
-# Isolate Fault  Trace confirmed that the I²C_AOP_SDA line runs under U4700 (Audio IC).  Remove U4700 → re-measure line → short clears.
+#** SCL (Clock Line): ~0.318 V (within normal range).
-# Confirm Diagnosis  Test boot with U4700 removed → phone boots into iOS normally (without audio).  This confirms U4700 was the cause of the short.
+# Isolate Fault  Trace confirmed that the I²C_AOP_SDA line runs under U4700 (Audio IC). Remove U4700 → re-measure line → short clears.
+# Confirm Diagnosis[[File:11-bootlooping front prox.png|thumb|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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