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iPhone 7 no Power, no short!

Hi all,

I bought an iPhone 7 that came with no power, no charging issue, and without water damage. The phone was never opened and the board looks brand new. So I decided to look for the problem.

After going with troubleshooting , and after pressing the power button, the phone was drawing around 0.6 Amps, but no shorts were found in all VCC lines (MAIN, BOOST, etc). In fact all the PP lines were with the right voltage values.

Because there was some small heating coming from the CPU side (I couldn’t verify which side -bottom or top- was heating first), I decided to remove the stickers. After that, I could’t find any damage or short, so I removed the CPU shield (same as I did before). Then, I checked all voltages and looked for a short on VCC lines, but everything seamed normal.

However………. the current draw is now around 0.03 Amps after removing the shield.

Any clue?

I am afraid that I had a damaged/broken CPU chip (maybe caused from a faulty charger?, which I cannot know because the phone wasn’t mine).

Did the heating (from removing the shield) revealed the real problem? Or is it just something else? Does anyone has faced this problem before?

Thanks in advance for any hints!

Regards.

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선택된 해법

What do you mean by “all the PP lines”? There are nearly 50 power lines in an iPhone 7…have you tested them all or just a few. As for the “VCC” lines, there are only two. Please be more specific about which lines you have checked and whether or not they were looked at in diode mode, voltage mode etc. The better the info you provide, the better the answers you will receive.

Working on dead iPhones requires a systematic approach when there are no obvious failures. You start with the three main lines, then Boost, then the main BL/LCM/Touch lines, then the PMIC outputs (switchers and LDO’s), then the BBPMU outputs and then whatever LDO’s you haven’t already looked at (Mesa, Mamba, Camera etc.). If you have any visible clues, like corrosion, burn marks or heat signatures, then you can focus on those first.

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It sounds like you have created other variables now besides the original problem.

• How do you know the phone charges if it doesn’t boot?

• Were you using a dcps or amp meter to obtain your readings?

• Was the phone boot-looping?

• Did iTunes recognise it?

A phone that is at 60MA would not in my opinion have a faulty cpu it would be waiting for some instructions from the nand. Hopefully you haven’t bridged any solder balls under the CPU. Go back over your steps and check everything you touched to get it back to the original state. Answer the above questions and we will be able to help.

Thank you guys for your helpful answers.

regarding my readings…

input voltage = 3.9V

VCC_BATdiode mode 0.464Vvoltage mode: 3.9V

VCC_MAIN - 0.336V

voltage mode: 3.9V, 3.88V after power up

VCC_BOOST 0.392V

voltage mode: 3.9V, 3.88V after power up

PP_LCM_BL_

diode mode 0.514Vvoltage mode 3.865V

I’ve tried a lot of PP lines. and still no clue. Maybe I will give up :D I actually don’t know the past of this phone. Fall? faulty charger?

I cannot go back to my previous state, because the only thing I did was removing the CPU shield, which I believe that putting it back won't help much.

Thanks.

So far everything looks good but there are several critical power rails that still need to be looked at. Go to the PMIC page(s) on the schematics and test all of those in diode mode with the device unpowered.

What was the solution? I have 2 of these phones in the shop with the same symptoms. No power, .03a draw on the power supply and .41a draw from the charge port. Could not find a short any where. Only difference was both phones arrived like this, one of them never opened before.

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