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Repair information and guides for the iPhone 6S released by Apple on September 25, 2015. Models: A1688, A1633

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Why missing battery sensor on OEM replacement?

Today I bought a fully functional iPhone 6s (never opened) to maintain another identical fully functional iPhone 6s (except storage capacity).

After replacing the battery by the (in fact genuine OEM!) donor battery, it restarted every 3 minutes.

Panic logs unveiled missing sensor TG0B (battery): iPhone Keeps Restarting

Returning to the currrent worn out battery* resolves this issue.

This is nuts. ^^ Couldn't find any question/issue/answer alike.

*Current battery is a 3rd party from a local repair shop that never caused any issues but lasts only 2-3 hours being 3 years old. Before this one there was an iFixit battery which lasted the same being 2 years old only.

Reference to question/answers on german board: https://en.ifixit.com/Antworten/Ansehen/...

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See https://repair.wiki/w/How_To_Fix_an_iPho... This explains the troubleshooting steps for a TG0B (battery) error in great detail

For iPhone 6s motherboard pinouts and diode mode readings read further HERE

Edit; addendum:

Luckily, diode mode readings are fairly reliable for finding what circuit is causing an issue. You want to use an ultra-fine probe to measure red on the pin and black on a nearby ground. The values will never be exact board to board and meter to meter. You're looking for a number far out of spec compared to a known working board.

This method works on any phone connector if you have a known good board handy.

When you have found an out-of-spec pin, you can inject 1V DC with a > 500mA current limit from a bench power supply and watch thermals for faulty parts, or use a rosin dispenser or isopropyl alcohol to visually spot heating components.

One more tip: minimal components to boot the 6s are the screen, battery, and charging port. Attach NOTHING else when diagnosing the board to eliminate as many variables as possible.

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It appears to me from the question that the issue seems to be definitively with the battery and not the motherboard.

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Thanks a lot for taking a closer look!

It seems this troubleshooter on TG0B refers to iPhone X and the relevant aspects do not apply to iPhone 6s. This model has neither MOSFETs Q3200 and Q3201 nor mentioned data pins - correct me if I'm wrong: https://electronics.stackexchange.com/qu...

Anyway, both iPhone 6s and all it's parts show absolutely no sign of damage/corrosion to any circuits, connectors, resistors, transistors, etc. though I don't have a multimeter with me to "prove".

The closer I look into it, the weirder it gets. :'D

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@pirfacsml65yffb best of luck diode mode readings are fairly reliable for finding what circuit is causing an issue. You want to use a ultra fine probe to measure red on the pin and black on a nearby ground.the values will never be exact board to board and meter to meter your looking for a number far out of spec compared to a known working board.

This method works on any phone connector if you have a known good board handy.

When you have found a out of spec pin you can inject 1v DC with a >500ma current limit from a bench power supply and watch thermals for faulty parts or use a rosin dispenser or isopropyl alcohol to visually spot heating components.

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@pirfacsml65yffb without a doubt invest in a multimeter I recommend kiweets or extech for a reliable accurate and cheap option. Fine needle tip probes usually need to be purchased separately.

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@adr_daniel Thanks a lot for these tips: red-probe on pin, other to ground; appropriate current for thermal testing, minimum configuration.* Nevertheless I don't see in this any promising progress on fixing this issue, because there is definitely no visible damage anywhere on current board, connectors, circuits and all parts of the donor phone look neat if not brand new.

So even if a faulty pin could be located with certainty

- what I doubt because of it's visual shape/state, given probability for just another dubious Apple vendor lock-in and requiring comparison to / insight in somewhat reliable specs taking some time to find too -

this wouldn't yield how to get this OEM battery accepted on the current board. Microsolder around randomly on a located pin an circuit? Definitely won't risk the device for that.

*I definitely would like to once look into this, microsolder around and a lot more. However, getting myself a multimeter only, would already end up in diving into this too much. :')

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Just to clarify, you bought another iPhone 6S, took the battery from it and put it in your own iPhone 6S, right? And the donor battery causes a boot loop in your current phone.

Question: does the donor phone also boot loop with that same battery?

If so, it's just plain a failed battery and you'll have to locate another replacement. Otherwise that's a new one on us. The only thing I can think of would be software; if the donor phone is running a newer version of iOS, it may have updated drivers that can handle a change in the battery communication protocol; that battery may be newer and require an OS update on your phone. That's all I can think of if it works fine in the spare phone but not yours.

Oh yeah, you might verify that your phones have the same model number; any chance you might have gotten a 6 instead of a 6S?

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1. Yes.

2. No, the donor iPhone 6s is fully functional.

3. Logs checked and tested before (genuine 1st) opening.

4. Both iPhone 6s have exactly the same version of iOS 15.8.4 (19H390).

5. Both iPhone 6s have no signs of any corrosion, water damage or alike. The worst I can imagine is past heat/sun exposure as the screen's adhesive strip looks a bit yellowish and dried out already.

6. Interestingly transferring various other parts is fine: iPhone 6s Lightning Connector Assembly Replacement, iPhone 6s Wi-Fi Diversity Antenna Replacement and even screen including front-facing camera + sensors, earpiece speaker and home button*. There is literally not much left to transfer: cellular antenna, rear camera, general speaker, taptic engine

7. Of course I did - both are A1688. Interestingly logs of both iPhone 6s show "Hardware Model: iPhone8,1"

*Ofc without Touch-ID which is well-known. Also I figured that double-tap (not double-click) does not trigger reachability mode for one-hand-use although it actually should.

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@pirfacsml65yffb Yeah, the hardware model number doesn't appear to have a direct relationship to the iPhone number, so 8,1 is perfectly reasonable.

I'm stumped with regard to the battery working in one phone and not the other unless there's some kind of variation in the two connectors; perhaps a pin is bent down just enough that your original battery makes good contact but the donor phone battery doesn't?

Alisha (@flannelist), have you got any ideas here?

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@dadibrokeit I'm stumped too, that's why I reached out to you.^^ But for the time I have this phone in use I won't fiddle around. I will return to this after switching to another device, if I got the time and a multimeter by then. ;)

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Summarizing the contributions of @adr_daniel and @dadibrokeit this issue answers as follows:

The donor OEM battery seems to be ok since it's running fine on the donor phone, as the current battery does too.

Some software issue is indicated since boot loop remains with the donor OEM battery on the current phone, but not with it's current battery.

Maybe some board issue is indicated too, despite no visual signs of corrosion / damage / impurities, because of observed long term increase of heat developement on the board.

However, any solution of the latter requires further diagnostics by a multimeter or tristar chip tester and most likely microsoldering (not feasible here).

Solution: Reset (software), further board diagnostics by multimeter or even tristar chip tester.

As a note see also: iPhone Battery Draining Fast

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