iPhone 8+ wont turn on and no connection on pc

Hi, I'm new to this world and I want to learn how to make repairs on motherboards, I picked up the phone on the internet, the old owner said it fell once and never came back on, after which he sent it to a technician experiencing a motherboard problem.

I firstly attached it to the 4.2 volt power supply and at power on it marked 200-300 mA, with the multimeter I checked VCC_BATT in the battery connection and it was normal, then I checked several capacitors in VDD_MAIN always in diode mode on ground and all ringed on both sides, does this mean that there is a short somewhere in VDD_MAIN? If yes, how can I understand which component to change?

Then I had read that with these symptoms it could be a problem with the USB signal and therefore to change U6200, I could not test the pins below because I still have to get the desoldering, but I checked a capacitor directly connected to the chip but it was normal . Im doing things the right way? Im a little confused, Thanks in advance.

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If it beeps on vdd main on both sides of the cap then yes there is a vdd main short. You could use freeze spray and inject voltage into the vdd main side of a capacitor

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Thank you very much, i've seen some videos of this tecnique and i'll give it a try, but how i do phisically inject voltage? i have two pliers attached to the dc power supply, i connect positive on ground and negative on the cap or i need to remove the cap and solder the wire on correct pad?

In my understanding that that get powered the VDD_MAIN circuit and the component wich is broken will show up first with the spray method right?

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