Iphone 6 not turning on.

[LetItFlowTech]

I received an iPhone 6 in today that came from another shop for a repair.

Original problem: no image or back light (phone was dropped) but iTunes recognized the phone when plugged into the computer. Shop said it could see users names in box. They tried different batteries and screen. Still no image or backlight. They did find C1552 was shorted and they replaced the cap. Still no image or backlight, so they changed out the U1502, L1503 and D1501. Still no image or backlight. However after that repair they can no longer get the unit to boot at all. Computer and itunes does not recognize the phone being plugged into sub port. So they sent the phone me to see what I can possibly do.

I looked over their repair and everything looks clean, good solder work. I plugged in the battery and I am getting 3.8v at test point PP0201. With a battery still plugged in I tested the voltage at C1552 cap that they replaced and I get 3.8v reading there without even turning on the unit.

So I hooked up the power supply, set the voltage to 4vdc and 2A of current. Just plugging in the power supply to the logic board without trying to activate the boot process no Amps are being pulled.

What should my next test be? Did the previous shop possibly damage an IC chip during the repair.

Hate to start replacing chips if unnecessary. How would I know if it's a bad power management chip, or q1403. I don't think Tigris or tristar would be the culprit but then again I could be wrong. Could the actual CPU have failed?

Any suggestions on where to start. If you need me up load any measurements definitely let me know what you want me to measure.

All suggestions would be greatly appreciated

[mark55]

65730AOP (u1501) display ic could possibly be the culprit for lack of display but you surely cannot be 100% sure the other place have fitted the correct value or working components.