Iphone 5s no boot

Hello boys. this is my first message I write. sorry for my bad english

I have a problem with a 5s. the phone turns on, appears the apple and then turns off.

sometimes absorbs 0.25A and fading, sometimes absorbs 2A and fading.

when I connect the battery and USB power manager becomes warm.

I checked:pp3v0_sdram pp1v8_sdram pp1v2_sdram. It is ok.

the line pp1v1_cpu pp1v1_gpu is short. the resistance to ground is 0ohm but when the phone is on and I measure the voltage it is 0,46v (pp1v1_cpu pp1v1_gpu)

anyone has any advice for me? thanks in advance