iPhone 7 boot looping and error 51 in iTunes

[Alber_the_Learner]

I got an iPhone 7 with no history of any damage stuck on the boot looping and getting error 51 in iTunes.

I'd like to learn more about the error 51 and I did not find any interested tips on google.

Any advices?

[darkwintercloud]

I'm sure its something related to baseband damage of insuficient energy supply (bad Baseband PMIC)

But since its a iPhone 7, maybe try to figure out if its related with the baseband recall Apple is doing is a good start point (check the model number and the serial number, if they match, maybe its a short inside the Baseband CPU and its still a no go for repairs)...

[Jessa_the_Professa]

Have you done rule #1? A guy at the course last week had an iPhone 7 boot looping with error 56 and it turned out to be parts. It works just fine in a total OEM housing.

[Alber_the_Learner]

Yes, I did! Happy Mother's day, Jessa Jones!!!!

[Alber_the_Learner]

Oh my gosh! I messed up the iphones 7 and their histories...

This one has another history. Let me update.

Customer sent it after another repair shop did not fix it.


DCPS:

The consumption goes up to 0.8A and then gets down to 0.1-0.2 than stayed in there at low consumption flutuacting.

There were several pads at USB docking port measuring OL.


VISUAL INSPECTION:

Tristar was missing.

There was a green resin and a jumer coming out from Audio IC (U3101) near by the C12 pad.


WHAT I DID:

I replaced Tritar. No more OL measuring on USB docking port.

On DCPS without booting I found a short 0.25A consumption.

I took the U3101 Audio IC off, cleaned the pads and the short was gone. There a couple of missing pads needing to be jumpered...

Then I tried to restore at iTunes several times and I am getting error 51 in about 50% of the Firmware restoration bar progress.

I have no idea what to do next...

Any advices?

[Jessa_the_Professa]

Error 51 gives us no information, it is not associated with any known faults. A phone that was missing tristar with audio ic replaced in a way that caused a vccmain short under audio ic means that it has been subject to repair attempts by someone who doesn't know much about board repair. From that history we can assume that they likely overheated bb_cpu on the opposite side of audio ic and may have misdiagnosed a bb_cpu signature problem from the beginning. I would not invest time into a board that has these kinds of variables and technician-created problems when there are thousands of boards out there that have native faults ready to repair. If I was forced to put time into it, I'd reball bb_cpu and take diode measurements while it was off.

[Alber_the_Learner]

Thank you Jessa for taking time in the Mother's day for giving me this advice! I will try to reball BB_CPU...

[crea2k]

One thing you could try is remove the bb_cpu and try and restore. It'll fail on the baseband section, but if it does as least you'll know the other error is gone as it tends to flash baseband towards the middle / end of the process.