What components are necessary for and iPhone to start?

Hey Guys!

Here’s my story.

I bought this broken iPhone 4s from a second-hand website for a good price, since like fixing iPhone and a spare (working) iPhone could come out handy. Guy said he just dropped it, screen cracked and it became unresponsive.

Disassembled the phone, found nothing really damaged. Unhooked al connectors, re-clicked them and reassembled the phone; still nothing.

Suspecting a battery problem, grabbed my multimeter and started checking the battery; 0v! Dancing my victory dance, I grabbed a battery I knew to be good and installed it. When I tried to start it, nothing happened on the screen, but I noticed the phone was heating up quickly at a specific spot, so I quickly unhooked the battery before the phone would fry it.

So it’s clear for me the phone is shorting out on a quite specific spot. Doing some research I came up the plan to hook the iPhone to a 3v adapter, and see where it’s heating up so I know what component (hopefully just a capacitor) needs replacing to fix the board. The question that follows from this: What do I need to keep hooked up to perform this test, eg: All buttons, screen and dock, or will it suffice to just take the mobo and hook it to the power supply?

Hope you guys can help me out, and maybe give me some tips to get this job done!

Thanks in advance!

Bart