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2017年9月に発売されました。モデル番号はA1863、A1905。GSM もしくはCDMA/容量は64か256GB/ゴールド、シルバーとスペースグレイ

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iPhone 8 in Boot Loop

Hi.

As a quick foreword, please forgive my somewhat broken English. You have a %#*@ froggy in the house.

I already posted my question on the French version of the site but never had any reply so far.

My iPhone 8 is stuck in a Boot Loop when I stop using it or when I try to shut it off. The phone is working fine (I can receive and send calls or sms and use the few apps installed). Here for the symptom.

I have to add that I successfully replaced the screen few days ago. I also had to replace the rear case. Unable to remove the original battery from the broken rear case (goddam adhesive strips that always break when you try to tear them off!). I ordered a new one (see picture 1 for reference) and put it in the new rear case.

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While I was putting back the components, don’t ask me what kind of a demon drove me to get my nose in the lightning port bracket. Anyhow, once it was unscrewed I discovered that the Wi-Fi Diversity Antenna (see picture 2) was connected to nothing. Then I decided to take the missing little connector (see picture 3) to put it in the new rear case. Have I done something wrong? Anyway I came up with the above described issue.

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Another useful information. I had access to the “Panic Full” bug reports from my phone, so here we go:

{"bug_type":"210","timestamp":"2025-11-26 19:07:45.00 +0100","os_version":"iPhone OS 16.7.12 (20H364)","roots_installed":0,"incident_id":"D4723989-757F-4BAB-8100-4B626F022541"}
{
"build" : "iPhone OS 16.7.12 (20H364)",
"product" : "iPhone10,1",
"socId" : "8015",
"socRevision" : "11",
"incident" : "D4723989-757F-4BAB-8100-4B626F022541",
"crashReporterKey" : "da6725d19f3ba5fa49be76cb94b0c9eb9c59eff8",
"kernel" : "Darwin Kernel Version 22.6.0: Tue Jul 2 20:47:35 PDT 2024; root:xnu-8796.142.1.703.8~1\/RELEASE_ARM64_T8015",
"date" : "2025-11-26 19:07:45.25 +0100",
"panicString" : "panic(cpu 0 caller 0xfffffff01eed0140): \"i2c3::_checkBusStatus Bus is still in a bad state; last write status 00010110 int shadow 00010100 xfer 00000000 fifo 00000000 for device lm3539\" @AppleS5L8940XI2C.cpp:451\nDebugger message: panic\nMemory ID: 0xff\nOS release type: User\nOS version: 20H364\nKernel version: Darwin Kernel Version 22.6.0: Tue Jul 2 20:47:35 PDT 2024; root:xnu-8796.142.1.703.8~1\/RELEASE_ARM64_T8015\nKernelCache UUID: C77F966291D7FB718E05F899C6EEC2BA\nKernel UUID: 28E24CE2-BA1C-38B1-AC56-C0BE08A077BC\nBoot session UUID: D4723989-757F-4BAB-8100-4B626F022541\niBoot version: iBoot-8422.142.2.700.1\nsecure boot?: YES\nroots installed: 0\nPaniclog version: 14\nKernel slide:

After a long research on Google I could figure out that the i2c3 error code may either involve the lightning cable or the display connector. Can someone come up with a clue or any answer. Thank you in advance.

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A boot loop on the iPhone 8 after a housing and battery swap is usually caused by an I2C line fault. Your panic log points to i2c3 and the LM3539, which is part of the backlight/power circuitry. That means one of the flexes connected to the logic board is either damaged, pinched, or not seated cleanly.

Most common causes after a rebuild:

– Slight tear in the display flex

– Damage to the backlight circuit near the connector

– Something shorted around the Lightning port bracket when you moved parts over

– A missing or incorrect screw (“long screw damage”) near the display connector area

I’d first recheck the screen connectors under magnification and inspect the bracket area you mentioned. If the loop continues, it’s usually a board-level fault. I’ve seen the exact error in repairs at my workshop (iRepairGuys Preston), and it ended up being a tiny I2C line knock near the display connector.

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Hi Sebastian. Thank you for your reply. I don’t know if you checked Jerry Wheeler’s reply. Anyway I followed his advice and replaced the Taptic Engine. I don’t know if the Taptic Engine from the brand new rear case was broken or if one the Wi-Fi Diversity Antenna connectors was not correctly seated during my repair. Anyhow this solved the problem.

Thank you very for taking the time to reply.

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I don't have access to iPhone 8 schematics, but I do have a set for the iPhone 8 Plus. Most of the signals and functions are going to be the same between the two, so be aware that my information is based on the 8 Plus, not the 8 itself so there's a small chance things could vary.

That being said, I'm tracing the i2c3 bus through the system, and the one thing that stands out to me is that one place it goes to is called the Sakonnet chip. This is the part that controls the Taptic Engine, and is located in the device itself. So my first suggestion would be to replace it and see if that clears up the issue. If you don't have a spare, you can try just disconnecting it; you'll probably still get a boot loop, but the error you get will be something related to a missing device rather than a stuck signal line.

The signal also goes to reference designation U3700, which is marked as "D2462-AVAE WLCSP", whatever the heck that is. It's on a page labelled Camera PMU, so I suspect it may have something to do with the flash. That seems to be reinforced, as it also goes to reference M4100 on a page labelled LED Strobe Drivers.

Another destination for that signal is reference U5650, which appears to have something to do with the LED backlight drivers. Finally there appears to be a connection to the EEPROM on the display as well.

Alisha (@flannelist), what do you think, would you go with the Taptic Engine as the likely source of the problem, given that's where François has been working?

Of course, it could also be a problem with the connector; if it's not plugged in fully it could cause issues like shorting that signal to ground, which would also cause that kind of problem. So double-check the connection between the Taptic Engine and the lighting connector assembly, as well as the big connector going to the motherboard. Basically take a close look at all the connectors you plugged or unplugged; I'd suggest a magnifying glass and a bright light to start with, looking for any bent or broken pins. Clean them all with 90% or higher isopropyl alcohol, give them a minute to dry, then reconnect and retest. If it still isn't working, I'd swap out the Taptic Engine and see if that fixes the problem.

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Hi Jerry.

Thank you for your in depth reply. Indeed I forgot to mention that the Taptic Engine is emitting a strange sound after the phone has restarted (just before entering the secret code). I just thought I had sticked the new battery too close from it, the strange noise resulting in the battery vibrating with the Taptic Engine.

Anyhow, I still have the one from my original rear case, so I will replace it and follow your first advice and let you know.

Thank you very much for spending such a long time for your (again) in depth reply.

Best regards.

François CROCY

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Ok. It just took me one hour or so to replace the Taptic Engine and Bingo! Bye bye goddam Boot Loop! Thank you so much Jerry for your valuable information. While at it, I decided to replace all the parts I could find from the original rear case (the Wi-Fi Diversity Antenna and the Lightning Port bracket). Then I noticed that the bracket in the new rear case was slightly different from the original one. For what it’s worth, here are pictures of both brackets. Thank you again for your contribution.

Original bracket

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New one (sorry, the picture is blurry).

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François CROCY さん、ありがとうございました！
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