An iPhone 13 Pro came in to me completely dead. The customer said she didn't water damage or drop it, and there were no signs of that. She needs data.
This was an interesting case and I want to share how I methodically track down motherboard problems and my reasoning behind my thought processes. The first step I always take with flat dead iphones is to check what my dcps amp draw looks like. I should note that in this case it was somewhat inconsistent, but mostly it would just stay at .05a after prompt to boot. Sometimes it would try to act like it was booting on dcps, but mainly we can think of it as a 50ma problem.
50ma problems are sometimes referred to as "brain dead" motherboards because in most cases it means that power rails are turning on, but there is still something preventing full boot up. It can even just be one of those power rails is missing. So the first thing I do when I have a 50ma dcps draw after prompt to boot is to make sure all the expected power rails turn on.
Many techs just stop here. Instead they start guessing.
I always check the power rails with a brain dead iphone. I check any lines with a coil around pmic, as most of those go to cpu. Only gpu lines won't be turning on, everything else will. I check ram lines by clicking on the spots I know power ram, and seeing if I can find caps to measure at. And I check NAND lines. I do this everytime I have a brain dead phone. Lots of people ask me for advice and this is always what I say, but most techs just won't measure power for some reason.
So I did this and I could not find any problems with any power rails. If all power rails are turning on, then I should have pc detect. Recovery mode is better, but dfu mode at least should be there if your power rails are turning on.
I could not get recovery mode or dfu mode.
This led me to suspect I might have a problem with the usb circuits. I removed kraken (formerly hydra, tristar) and to really make sure I had no problems I checked diode mode measurments on each pad. But each pad seemed to be normal.
I also decided that it would be a good time to check the power rails that power kraken. We do not have net names on iphone 13 pro so we have to think outside the box. This was easy, I knew iphone 12 had the same chip, so I just referenced the 12 pro boardview instead. I noticed it had a 3v0 and a 1v2 power rail.
With the chip still off the board, I plugged in the battery, prompted the phone to boot and checked if the voltages were present. I first made sure normal power rails were still turning on, and they were. I then checked the 3v0 line and it was on. I checked the 1v2 line next and it was only .6v
I wasn't sure if this was because the chip was off the board, so I grabbed a new kraken ic and placed it on the board. With the new kraken, it still was not booting, and the 1v2 line was still only .6v
I had already checked diode mode and knew the pad was not short. This was good, because that line also goes to the cpu. So that led me to believe the pmic was not supplying the normal power and replaced pmic.
Once pmic was replaced, the phone booted up. I went back and checked the 1v2 line and saw that it was the normal 1.2v.
Now it is connected to the computer and data is being pulled.
This is why I love iPhone data recovery. There is a reason for everything, and if you can get good at identifying the problem, you can solve hard problems fast. This could also have been solved with a cpu swap, but by having a clear plan I was able to avoid that work. I have also avoided completing cpu swaps in the past that I knew had no hope by knowing which line was bad beforehand and measuring directly on the cpu. So diagnosis is your friend.
TLDR; No power, change power chip 100%