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Repair information and guides for the Apple iPhone 5s that was announced on September 10, 2013. Model: A1533, A1453, A1457, A1528, A1530, A1518

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Reading Schematics - Overview of main power rails?

Hello,

at the moment I am trying to get into the topic of board repairs but I got a little problem in troubleshooting the board of iPhones. I watched guides and explanations on which parts a board consists of and what every part does (rails, resistors, capacitors etc.). After that I looked for videos on how to start troubleshooting logic boards but I only found videos about troubleshooting boards from laptops. Here they always started with measuring the main power rails which was pretty much comprehensible. It seemed pretty easy because all the power rails were listed on one of the first pages of the schematic. You could easily see on just one page which the main rails are and so on.

But with iPhone boards I had to find out that there is not an overview about the rails in the schematic. It kind of just starts with the 'details' and doesn't priorly explain which the main power rails are, which voltage they have and so on.

So have I maybe overlooked something? Or how can you easily find out which the main rails are without working through 50 pages of the schematic?

Answered! View the answer I have this problem too

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If you look at some of the older iPhone schematics, like the 4/4S, they are more detailed. I believe that as third party iPhone board level repairs became more prevalent, the schematics became less clear...probably by design.

That said, there are a few power rails you need to check first: PP_BATT_VCC, PP_VCC_MAIN & PP5V0_USB. Check for shorts and then for voltage. That is what ultimately powers the phone (or iPad) and it is controlled by Tigris in the newer devices and the PMIC in the older ones.

Then you move onto the main power IC (PMIC or PMU) and check all the rails it generates. They will power the NAND, SDRAM, CPU, GPU etc as well as secondary components. Some peripherals have there own power chip, like the 2.85V line. If you have a bad rail on the PMIC, it could be a short along the rail or a defective PMIC. That's when you start removing components...

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Thank you so much, this was what I was looking for :) Helped me out a lot!

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@vorsichtkarsten a schematic alone is not going to work for you. You do require the boardview which will also show you individual nets (circuits) and which parts are in that particular part of the circuit

Update (01/07/2017)

@vorsichtkarsten there is more to the boardview, since it does more than just identify a single component. It will also show you which other components belong to that circuit. For my limited work I use a program called "Pads" (some people prefer ZXW tool) and the layout files for a particular circuit board. Let's say I needed to find the "PP3V0_USBMUX" (You know it will have 3.0V by the PP3V0_USBMUXI )for an iPhone 5. On my layers view I select that net and get this result

Block Image

Block Image

Now I know where and which parts are involved.

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I know, that was also shown in all the guides I was talking about. They used these boardviews mainly to find out where a particular part is that is shown in the schematic. But that was not really my question. So my question is still, how do you find out (in the best case as easy as with Macbooks) which the main power rails of an iPhones logic board are? As I said before, at the schematic of laptops you can find an overview about the main rails on one of the first pages. With an iPhone there isn't such an overview, so how do you find the main rails?

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Thanks for the update and the programs, really cool! I would accept your answer but unfortunately you can only accept one at a time :(

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Right now the board I’m working oniPhone 5 it has no PP5V0_USB does it mean that I have defective PMIC? What I observe is the PMIC is not getting hot… and at the upper side of the board is getting hot…away from PMIC.

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