iphone 8 diagnosing a short?

[lots2learn]

iphone 8
Activation locked iphone 8. Booted fine to the activation locked screen. Disassembled and removed the motherboard, desoldered shields on the CPU side. A component dropped off(see highlighted IC in attachment). I've desoldered many many shields on iphone 7, 7 pluses with no issue - this is my first iphone 8.

DCPS - 3.8v Max current draw set to 3A.
Connect up the motherbaord and screen only
Screen does not come on
Immediate current draw of 1.25A fluctuates down to 900mA - 790 mA DCPS - Volts Do NOT drop but remain at 3.8V.
PTB USB immediate current draw 330mA
Screen does not come on
Not recognised by computer/3U Tools.

If there were a short on VDD_MAIN I would expect the voltage on DCPS to drop? The screen does not come on but I think this is a secondary issue. I don't think that a screen issue would stop the phone from completing its boot sequence.
Can't glean any clues from a visual inspection.
Applied freeze spray down the bottom of the board. Connect to DCPS Tigris gets hot immediately as do the components in the same area as Tigris on the opposite side of the board.

[Jessa_the_Professa]

Why were you taking off the shields? Did you have a reason? If not—don’t take them off “just to have a look” for exactly this reason. Removing shields is invasive and causes problems. I don’t think I’ve ever taken off the bottom area shield on iPhone 8 because there is nothing under there that has ever gone bad, and I would not want to risk heat at trinity chip—same reason you’ve already learned when you created a main short at trinity.

only your multimeter can tell you what line is short. What is your diode mode reading on main?

[Jessa_the_Professa]

Also—are you sure you didn’t nudge the RF chips under that bottom area shield? It doesn’t look normal.

[lots2learn]

Yes I nudged them alright. Restored. Trinity was causing a short on VDD_MAIN. Replaced, relieved.

Current behaviour....
PTB USB - Hung on Apple logo
20mA, 80mA, 110mA(split second 350mA sometimes 430mA, drops back to 110mA)
stays stuck on 110mA
cuts out(screen goes black)/repeats(Apple logo)

DCPS 0mA B4 PTB
PTB DCPS - Hung on Apple logo
incremental current up to 200 - 210mA, brief trip up to 430mA - 570mA drops back to 200mA
cuts out(screen goes black)/repeats(Apple logo)

Given my previous desoldering/soldering efforts I am wondering how I should interpret this current draw?

[Jessa_the_Professa]

Boot loop is a form of brain dead. Restore to rule out software.

[lots2learn]

Assembled into frame booted into restore mode via DFU Box-C2

Connected to 3u Tools Downloaded firmware.

Phone went blank, dead - wouldn't commence restore/update process.

Shut down 3U Tools, reconnected phone to computer in restore mode

Restarted 3u Tools and commenced quick flash with downloaded update

phone booted with Apple logo, progressed to 19%, then screen went blank.

3u Tools stuck on progress at 19% 'Restoring'

What do I conclude from this?

[Jessa_the_Professa]

19% is the same as you would get if the device had no NAND.
trinity contains the eeprom in iPhone 8, you’d have to do an experiment to see if missing Eeprom fails at 19%, but it sounds likely.

I would reball trinity carefully, and then consider reballing nand and looking for loose resistors from that shield removal heat around the nand area.

[lots2learn]

" trinity contains the eeprom in iPhone 8" This statement has had me confused for nearly a month now.
I've searched for all eeprom entries on the iphone 8 plus schematics(there aren't any for iph8) and come up with nothing I can see that leads back to trinity. My understanding is that Trinity is just one great big array of power boost coils. Can you clarify? Which eeprom are you referring to? My understanding is also that EEPROM will contain SERIAL information etc that is unique to the phone? If EEPROM is actually contained within trinity wouldn't that mean that Trinity can't be replaced(at least not directly without reprogramming EEPROM. Pretty confused.

[Jessa_the_Professa]

look up i2c4_sda line in iphone 8. This is the eeprom signal, and it lives within trinity in the iPhone 8. You are correct--trinity can not be replaced without restore in iPhone 8