iPhone 7 wont prompt to boot.

[GHI888]

I have a iPhone 7 PCB, it has no prior repair. No history of water damage and no dents on the housing as well. It wont boot. When prompt to boot on DC power supply its giving me a loop of 0.7A then 0.16A and 0.01A again and agian on a loop. First I thought its a tristar, but after tristar replacement still the same. BTW when prompt to boot did not detect any heat. And when charged on the USB amp meter it gives me a loop of 0.12A then zero. Cant seem to figure out what the fault here, Is it PMIC?

[Jessa_the_Professa]

We can never know what it is. All we can do is weigh variables, looking at a story like a detective and trying to stick to the most likely path.

which sounds more likely to you-- (there is no right answer, it is just forcing you to guess)

1--The power management chip is able to generate all its baby voltages just fine initially and then it quits, and tries again because the chip is bad.

2--the power management chip is fine, but the software has been corrupted at some point, maybe failed update, maybe bad Tristar scrambled some data lines earlier, maybe nand filled with errors because some camera was bad.... Now the phone starts to boot but can't read the instructions so it says "I don't know what to do next" and restarts itself.

what do you think?

[tinker_techguy]

I think, if losing data is not an issue. We could rule out software by doing a DFU restore flash. After a flash it will either work or not. If not don't work at least we get more clues with an error code which may help lead us closer to a solution.

[GHI888]

I cant restore the unit since the customer forget her Apple id password.

if its Option No. 1 then i have to replace PMIC?

[Jessa_the_Professa]

Your job is to tell which is more LIKELY. Fault #1 or Fault #2. You can't force a problem to be what you want to solve. The problem is what the problem is whether you like that problem or not. So which is more LIKELY. Your goal is to learn to weigh possibilities and sort by order of likelihood.

[GHI888]

I'm thinking that Fault #2 is more likely, but the only way I know how to fix a faulty software is doing DFU mode and flashing it, is there another way?

Fault #1 I can be ruled out by replacing PMIC but I think its not likely to be a PMIC Fault.

[Jessa_the_Professa]

Right. It is FAR more likely that this is a software fault. Software faults happen all the time. Whereas I've never seen an iPhone 7 PMIC just stop working for no reason. That's unheard of, there is no mechanism for that to happen. Replacing PMIC would almost certainly be a waste of time and difficult to execute.

If you think the MOST LIKELY fault here is software (I agree) then software update and/or restore would be the next step. I would try update first. Put the phone in recovery mode with vol down and USB and see if it can pass iTunes update.