iPhone 5 wont power on, Case getting extremely hot.

This is an old iPhone I have had in a cupboard for years. Previously it was working. There is no sign of water damage inside the unit. The iPhone is pretty much factory standard apart from the addition of the new battery. It has never been dropped or damaged in any way.

Initially when I had a look inside I found the battery ribbon cable was brittle and it broke quick easily so I ordered another one thinking this would resolve the issue. After receiving and installing the battery the iPhone was connected to USB power. The current draw from charger was only 0.25A and there was no fluctuation . Pressing the power button did not change the current draw at all. Both sides of the motherboard were felt to be very hot to touch around the central areas of the shields. Possibly a short.

I have completely removed the motherboard and have applied 5Vdc/ 2A to the motherboards charging connector via a bench power supply. No current draw observed from the bench power supply, so I am assuming there is no short to ground.

My next step is to remove the shield and have a poke around. I have the diagrams and board-view details on hand.

This is just a bit of learning experience for me as I am keen to learn more about electronic troubleshooting. I could quite easily just chuck it back into the back of the cupboard and crack open a beer and watch Netflix or something but where’s the fun in that eh!

So I was just wondering if any of you guys have an inclination as to what the issue could be. From the YouTube research I have done I’m thinking it could be the Power Management IC, however would that prevent the iPhone from booting up?

i was hoping there was going to be a short to ground however the bench supply states otherwise. It’s also confusing why the motherboard is getting so hot with only 0.25A. I have one of those USB charging thingies that connects directly to the motherboard charging port winging its way to me. I’ve already got the Mechanic iBoot but this only starts from the iPhone 6 upwards.

Any feedback would be hatefully appreciated. If there is any other info required just let me know and I’ll post it up if I can.

Many thanks in advance…

Cheers

Johnny