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Repair information and guides for the iPhone 8 that was released on September 22, 2017. Model: A1863, A1905

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Help with iPhone 8 not responding nor powering on

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I've got an iPhone 8 that worked fine, it had no issues with booting, running or charging. The screen was slightly cracked and the glass on the back case. It was dropped. But like I said everything ran fine for a long time.

I ordered a new screen original and the back housing. (The back housing I ordered was with all small parts and components but they later messaged me it was out of stock so I said cool just send me the housing and I'll transfer all the small parts over). So the back housing came and I transferred everything over. When I went to boot up the phone to turn it on it went into boot loop. Turned it off, re checked everything and found the very small flex plug which I believe is the Antenna flex to be broken. (I have attached a photo of it so you can see which one I'm talking about).

After trying to turn the phone on again it did not respond or turn on. I found it strange that one second its in boot loop and next second its unresponsive. So I measured the voltage in the battery, was fine 4.13 v. I tried plugging power into the charging port and neither did the charging logo appear on the screen. Nothing at all.

So I'm thinking:

1- Screen cant be dead cause it just worked.

2- Tried plugging it into itunes encase screen was dead but phone was on (that was not the case itunes did not detect it so phone was off).

3- Battery is fine as tested with multi-meter.

I have tested all the pins by known good readings for the J6400.

Most where fine apart for these which I found a bit high.

Pin 6 - 0.802

Pin 8 - 0.802

Pin 20 - 0.805

Pin 22 - 0.802

Pin 24 - 0.802

Pin 25 - 0.721

Pin 26 - 0.907

Pin 27 - 0.721

Pin 39 - 0.612

Pin 41 - 0.612

(All diode readings)

And maybe 50, 53, 54 and 56 (all at 2.32) is a bit high what do you think?

From your experience by the readings I provided do you think there is an issue with the U2700 power IC? Or could it be an issue with the original charging port when it was removed and put back into new housing??

What I have done is ordered a new housing with all small elements already installed. If that does not resolve the issue will try replacing the power IC. I know that it regulates power to the phone and also charging, so if the phone is unresponsive it could be due to this.

Please let me know your opinion on all this.

I appreciate it.

Update (09/27/2020)

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Here is the picture I forgot to post

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The picture is not attached...

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I've added the photo

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Here is J6400. I don’t know where you got J4101 from. If you are trying to sort out a charging problem you are looking in the wrong spot.

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Hey Chris,

Thanks heaps yeah your right my bad, it is J6400.

Was late last night and messed up the port number hahaha

But thanks heaps you've helped me out.

Cheers mate

Tommy

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

Hey Chris,

I've got an iPhone 8 that worked fine, it had no issues with booting, running or charging. The screen was slightly cracked and the glass on the back case. It was dropped. But like I said everything ran fine for a long time.

I ordered a new screen original and the back housing. (The back housing I ordered was with all small parts and components but they later messaged me it was out of stock so I said cool just send me the housing and I'll transfer all the small parts over). So the back housing came and I transferred everything over. When I went to boot up the phone to turn it on it went into boot loop. Turned it off, re checked everything and found the very small flex plug which I believe is the Antenna flex to be broken. (I have attached a photo of it so you can see which one I'm talking about).

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

After trying to turn the phone on again it did not respond or turn on. I found it strange that one second its in boot loop and next second its unresponsive. So I measured the voltage in the battery, was fine 4.13 v. I tried plugging power into the charging port and neither did the charging logo appear on the screen. Nothing at all.

So I'm thinking:

1- Screen cant be dead cause it just worked.

2- Tried plugging it into itunes encase screen was dead but phone was on (that was not the case itunes did not detect it so phone was off).

3- Battery is fine as tested with multi-meter.

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

I have tested all the pins by the reading you provided in the J6400.

Most where fine apart for these which I found a bit high.

Pin 6 - 0.802

Pin 8 - 0.802

Pin 20 - 0.805

Pin 22 - 0.802

Pin 24 - 0.802

Pin 25 - 0.721

Pin 26 - 0.907

Pin 27 - 0.721

Pin 39 - 0.612

Pin 41 - 0.612

(All diode readings)

And maybe 50, 53, 54 and 56 (all at 2.32) is a bit high what do you think?

From your experience by the readings I provided do you think there is an issue with the U2700 power IC? Or could it be an issue with the was the original charging port was removed and put back into new housing??

What I have done is ordered an new housing with all small elements already installed. If that does not resolve the issue will try replacing the power IC. I know that it regulates power to the phone and also charging, so if the phone is unresponsive it could be due to this.

Please let me know your opinion on all this.

I appreciate it heaps.

Thanks mate

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

What is doing my head in that everything worked in the old cracked housing and display. And not just a bit it worked for a long time. And now all of a sudden nothing

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Housing replacements are notoriously difficult. The ones that come pre-populated can have low quality, if not outright defective flexes and doing it yourself exposes you to a ton of variable if things dont work.

As for your diode readings, the ones you have to worry about are low numbers or shorts (except for ground ;-). Did you put the red probe on ground and probe with the black lead? Your numbers seem high.

I would start by testing a bare-bones setup. Start by disconnecting the battery first (always!). Then disconnect the digitizer, LCD, front camera, rear camera and home button extension flex. Now re-connect the battery; you should only have the battery and Lightning Dock flex connected. Connect a known-good, preferably Apple-original Lightning cable to an iTunes enabled computer.

Does iTunes recognize your phone? If so, then you should re-connect one flex at a time until the phone stops working. I would start with the Home button flex first, then add the rear camera, LCD & Digitizer then from camera flex.

If the bare-bones setup does not get recognized by iTunes, then you most likely have a logic board issue. You could send it (or find a local) to a repair shop that specializes in micro-soldering repair.

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Please note, I merged your two questions. Please avoid asking duplicate questions.

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

Hi, Thanks for the reply. I've done a couple of them already iPhone 7, iPhone X and never had an issue. So not sure what happened here when everything was working. I also done some logic board repairs and micro-soldering. So I am looking at fixing it myself. From the readings on J6400 what does that tell you?

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@Tommy Duris It will have nothing to do with U2700. Mino is right about housing replacements. The first rule when repairing phones is rule out parts. I would put the logic board into a known good housing and test before you did anything else.

What you would have been looking for on the dock connector would have been open or shorted lines which there are not.

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Thanks Chris, legend mate. I've got some updates. Did some further digging around in the phone.

I've got another original iPhone 7 screen here which I forgot about. So I decided to plug that one in just for fun but it has a home button from another phone. Plugged in only the Volume buttons flex so I could turn the phone on, the dock connector and the digitizer with home button. Phone turned on which was great but in boot loop. Even managed to put it in DFU mode. So at least I now know that the problem was with the screen, bought it from fixservis.sk which is a bit phone parts provider in the Europe but like I said I already sent them a message that I suspect the screen is not original and also might be used and faulty. so waiting to hear back from them. So I'm a bit closer to fixing the phone.

What i'm going to do in the morning is re connect all the other plugs and see if the phone turns on normally without the boot loop.

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What hardware would cause the iPhone 8 to go into boot loop if not plugged in? Is there any?

So like I said the phone worked in the old broken case. And I did not drop it from then till now just putting it in a new housing. So I find it hard to believe that it could be a deeper motherboard problem. Will keep investigating but appreciate the feedback allot mate. Cheers again @imicrosoldering

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