|Needs equipment=Screwdrivers, known good parts, spudger
|Type=Part replacement
|Difficulty=1. Easy
}}
==Problem description==
There are many reasons that could cause an iPhone 15 and iPhone 15 Plus to randomly restart every few minutes.
For the iPhone 15 series, there are some sensors within the parts of the phone that are required to be plugged in & detected. Otherwise, the phone restarts on its own.
The device arrived with the numeric keys on the internal keyboard non‐functional, despite a complete keyboard replacement. Visible moisture and sulfation were detected near the keyboard’s SPI controller (U4801).
* '''Back Glass/Wireless Charging Flex'''- This is the flex that is attached to the Back Glass. It can damaged during a drop or screen replacement
*'''Proximity Flex''' -This is the flex that is attached to the screen. It can easily be liquid damaged or torn during a screen replacement.
*'''Charging Port Flex''' - This is the flex towards the bottom of the phone. It is easily damaged with a drop & the back glass is breaks. Or when someone has repaired the back glass.
🔍 '''Step-by-Step Diagnosis'''
==Symptoms==
Visual inspection: Corrosion was found near the keyboard/trackpad controller area (U4801).
*After a back glass repair, the iPhone will restart on its own every few minutes
*After a hard drop, the iPhone will restart every 3 minutes.
*After a screen repair, the iPhone will bootloop every 3 minutes
*The iPhone will reboot randomly when using it.
*The iPhone will seem to freeze and restart every 2-5 minutes.
*[[File:IPhone 15 - FPCs to Inspect for 3 Min Restart.png|alt=iPhone 15 - FPCs to Inspect for 3 Min Restart|thumb|iPhone 15 - FPCs to Inspect for 3 Min Restart]]
Voltage drop across R4814 (relevant resistor in the SPI circuit) was checked and confirmed expected values.
==Solution==
'''''Chip replacement attempts:
===Diagnostic Steps===
'''
'''First attempt:'''
Replaced U4801 with a donor chip from board 820-3476 (MacBook A1502).
🟡 Result: Keyboard worked, but Caps Lock LED was reversed (lit when lowercase, off when uppercase).
Before you start blindly replacing parts, it's important to try to confirm what is causing the restarting issue by reviewing the Panic Log file. This is a file that is generated by the Operating System, to document the fault causing the restart.[[File:Panic Log List.png|thumb|An example of panic log files you'll find in the iPhone when it has been randomly restarting.]]To find the panic log on the device, go to Settings-> Privacy-> Analytics & Improvements-> Analytics Data-> Scroll down to the files starting with "panic-full..." & click on the most recent dated file.
Then you'll want to scan through the text for keywords that may point you to the cause.
'''Second attempt:'''
For this model, look for where it says "SMC PANIC - ASSERTION FAILED" ... "Sensor Array" .. "0x...."
Used a chip from MacBook A1278 (Unibody).
If you see:
🔴 Result: Severe input delay, no trackpad and overall poor keyboard behavior.
*'''0x200000''' - it's the Wireless Charging Flex (Back Glass)
**Make sure it's plugged in & the flex is not torn
**Check that there's no liquid damaged, or that it's defective
**Test with OEM or Premium. Aftermarket Flexes have a high defect rate
**Diode mode the FPC connectors for any faults
**Could be a sandwich issue
'''Final solution:'''
*'''0x80000''' - it's the Charging Port Flex and/or Air Pressure Sensor
**[[File:IPhone 15 - Charging Port Flex.png|alt=iPhone 15 - Charging Port Flex|thumb|iPhone 15 - Charging Port Flex]]Make sure this flex is plugged in
**Make sure the Air Pressure Sensor is plugged in
**Check that no flex is torn, liquid damaged, defective
**Test with OEM or Premium. Aftermarket parts have a high defect rate
**Diode mode the FPC connectors for any faults
**Could be a sandwich issue
**[[File:IPhone 15 Air Pressure Sensor.png|alt=iPhone 15 Air Pressure Sensor|thumb|iPhone 15 Air Pressure Sensor]]
Replaced with U5701 from donor board 820-3332.
*'''0x100000''' - it's the Proximity Flex Cable
**Make sure this flex is plugged in
**Check that no flex is torn, liquid damaged, defective
**Test with OEM or Premium. Aftermarket Flexes have a high defect rate
**Diode mode the FPC connectors for any faults
*'''0x280000''' - it's the <u>Wireless Charging Flex</u> + <u>Charging Port Flex</u>
**Make sure both flexes are plugged in
**Check that no flex is torn, liquid damaged, defective
**Test with OEM or Premium. Aftermarket Flexes have a high defect rate
**Diode mode the FPC connectors for any faults
**Could be a sandwich issue
✅ Result: Keyboard fully functional, Caps Lock LED working properly, no delay, trackpad also fully operational.
* '''0x380000''' - it's the Wireless Charging Flex + Charging Port Flex + Proximity Flex
** Make sure all 3 flexes are plugged in
** Check that no flex is torn, liquid damaged, defective
** Test with OEM or Premium. Aftermarket Flexes have a high defect rate
** Diode mode the FPC connectors for any faults
** Could be a sandwich issue
'''⚙️ Technical Conclusion'''
The U4801/U5701 keyboard SPI controller contains firmware/configuration specific to each board model. These chips are not freely interchangeable between different MacBook series (A1278, A1502, A1398, etc.).
Alternatively, you can use a tool like the [https://github.com/waynebonc/iDeviceLogAnalyzer-public iDevice Panic Log Analyzer], which will download the panic logs from the device & display them on the PC & give you suggestions to possible solutions. It makes it easier to browse the panic log file.
⚠️ '''Using an incompatible IC can cause:'''
Also check out [https://Www.PanicFull.com www.PanicFull.com] which allows you to upload the panic log file & have it analyzed for free.
Reversed Caps Lock LED logic.
Both of these tools just give suggestions, which aren't always correct, as there is no official solution list from Apple. So many solutions are just suggestions based on hearsay, rumors or just guesses.
Noticeable input delay on keys input.
For situations where you don't see the above examples, you'll have to read through the top portion of the panic log & try to decipher what could be the root cause. Look for keywords you may recognize.
Malfunctions with the trackpad or power button.
===Repair Steps===
When trying to solve for these issues, make sure to replace the appropriate flex with an OEM or Premium flex.
✅ '''Key Takeaway'''
It is also a good idea to keep a known good power button flex & charging port flex in your bench, for testing only. There are reports of even NEW flexes being bad. So you have to keep known good flexes on hand at all times, so you don't waste your time troubleshooting with possibly bad flexes.
“The keyboard IC (U4801/U5701) must come from a firmware-compatible logic board. Although they are electrically identical, their internal configuration depends on the board model and its interaction with the SMC.”
In scenarios where you have the appropriate flexes plugged in, but it still restarts, then you either have:
— Diógenes el Perro
🛠️ Note: Neither the BIOS nor the SMC were reprogrammed during this repair.
*Bad or damaged flex
*Low quality aftermarket flex
*Other flex cables that are Liquid Damaged
Please note: You MUST have the required flex cables plugged in. Otherwise, it WILL restart. You cannot troubleshoot this step by unplugging the bad flex.
Revision as of 18:20, 19 September 2025
How To Fix an iPhone 17 Air That Randomly Restarts
There are many reasons that could cause an iPhone 15 and iPhone 15 Plus to randomly restart every few minutes.
For the iPhone 15 series, there are some sensors within the parts of the phone that are required to be plugged in & detected. Otherwise, the phone restarts on its own.
The most common for iPhone 15 series are:
Back Glass/Wireless Charging Flex- This is the flex that is attached to the Back Glass. It can damaged during a drop or screen replacement
Proximity Flex -This is the flex that is attached to the screen. It can easily be liquid damaged or torn during a screen replacement.
Charging Port Flex - This is the flex towards the bottom of the phone. It is easily damaged with a drop & the back glass is breaks. Or when someone has repaired the back glass.
Symptoms
After a back glass repair, the iPhone will restart on its own every few minutes
After a hard drop, the iPhone will restart every 3 minutes.
After a screen repair, the iPhone will bootloop every 3 minutes
The iPhone will reboot randomly when using it.
The iPhone will seem to freeze and restart every 2-5 minutes.
iPhone 15 - FPCs to Inspect for 3 Min Restart
Solution
Diagnostic Steps
Before you start blindly replacing parts, it's important to try to confirm what is causing the restarting issue by reviewing the Panic Log file. This is a file that is generated by the Operating System, to document the fault causing the restart.
An example of panic log files you'll find in the iPhone when it has been randomly restarting.
To find the panic log on the device, go to Settings-> Privacy-> Analytics & Improvements-> Analytics Data-> Scroll down to the files starting with "panic-full..." & click on the most recent dated file.
Then you'll want to scan through the text for keywords that may point you to the cause.
For this model, look for where it says "SMC PANIC - ASSERTION FAILED" ... "Sensor Array" .. "0x...."
If you see:
0x200000 - it's the Wireless Charging Flex (Back Glass)
Make sure it's plugged in & the flex is not torn
Check that there's no liquid damaged, or that it's defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
Could be a sandwich issue
0x80000 - it's the Charging Port Flex and/or Air Pressure Sensor
iPhone 15 - Charging Port FlexMake sure this flex is plugged in
Make sure the Air Pressure Sensor is plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket parts have a high defect rate
Diode mode the FPC connectors for any faults
Could be a sandwich issue
iPhone 15 Air Pressure Sensor
0x100000 - it's the Proximity Flex Cable
Make sure this flex is plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x280000 - it's the Wireless Charging Flex + Charging Port Flex
Make sure both flexes are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
Could be a sandwich issue
0x380000 - it's the Wireless Charging Flex + Charging Port Flex + Proximity Flex
Make sure all 3 flexes are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
Could be a sandwich issue
Alternatively, you can use a tool like the iDevice Panic Log Analyzer, which will download the panic logs from the device & display them on the PC & give you suggestions to possible solutions. It makes it easier to browse the panic log file.
Also check out www.PanicFull.com which allows you to upload the panic log file & have it analyzed for free.
Both of these tools just give suggestions, which aren't always correct, as there is no official solution list from Apple. So many solutions are just suggestions based on hearsay, rumors or just guesses.
For situations where you don't see the above examples, you'll have to read through the top portion of the panic log & try to decipher what could be the root cause. Look for keywords you may recognize.
Repair Steps
When trying to solve for these issues, make sure to replace the appropriate flex with an OEM or Premium flex.
It is also a good idea to keep a known good power button flex & charging port flex in your bench, for testing only. There are reports of even NEW flexes being bad. So you have to keep known good flexes on hand at all times, so you don't waste your time troubleshooting with possibly bad flexes.
In scenarios where you have the appropriate flexes plugged in, but it still restarts, then you either have:
Bad or damaged flex
Low quality aftermarket flex
Other flex cables that are Liquid Damaged
Please note: You MUST have the required flex cables plugged in. Otherwise, it WILL restart. You cannot troubleshoot this step by unplugging the bad flex.
