iphone 7 plus Voodoo short on VDD_MAIN

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

iphone 7 plus Firstly I proofed a non working vibrator to be a motherboard issue.

C3537 which is off PP_ARC1_VBOOST tested short.

Seeing no discoloration or physical signs of damage on it or any other caps on that line I concluded the speaker Amp that powers the vibrator - U3502 was the most likely candidate. I removed and the short was relieved. So I replaced it with a new one.

Replacement Speaker Amp moved a bit during the reseat so I decided to diode test VDD_MAIN before powering up - dead short. Removed the new speaker amp IC, clean lift and there was no bridging underneath.
VDD_MAIN still dead short. Applied freeze spray, powered up on DCPS and the mosfet was the first thing to get hot - but the mosfet has no path to ground - I don't think it is the cause of the short.

Aside from an audio IC jumper repair I did two months ago there is no prior work, and the phone, excluding the vibrator(which never worked) has been working fine -until now.
Where to?

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

Immediately pulls 2.4 Amps on DCPS before PTB. Mosfet is the first to get hot on the entire board (I also applied freeze spray at the top of the board where PMIC and audio IC is)and the heat spreads out as per attahed images 1,2, 3

[Jessa_the_Professa Member Find all posts View Profile Close Jessa_the_Professa]

Only a thin wire will get hot, and usually the short is caused by the creation of a thin wire. In your case, the most likely problem here is a thick wire--main is blobbed into ground either under a chip that you nudged with the speaker amp work or at trinity because trinity is a coil array and hates to get hot.

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

Thanks Jessa. I know I didn't nudge anything so I desoldered Trinity. Clean lift - no bridging under Trinity. But diode mode shows the short on VDD_MAIN now relieved. I only applied 385 degrees at 100L for 45s from my Quick Hot Air station to remove the speaker Amp IC - I'm surprised Trinity went bad.

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

Stole Trinity off an activation locked board. Retested and the short is back again. *mother*

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

Desoldered Trinity that I got off the activation locked board and checked. It too had developed a short. Took a fresh one off the strip and soldered. Took about 20 seconds(instead off my usual 40-50s)No shorts and now the phone boots fine. When I reballed the harvested IC I reballed it with normal sized balls but the balls on the replacement ICs are virtually non existent. Restored the speaker Amp - still no vibrator. I'll have another go.

[crc2018 Forum Subscriber Find all posts View Profile Close crc2018]

Had a quick read of this 100L on a quick for air flow sounds way too high for iPhone board work! You have probably overheated trinity using such a high flow! I'm using between 40-60 maximum when working on iPhone boards!

[lots2learn Friendly Contributor Find all posts View Profile Close lots2learn]

Thanks crc2018. I'll experiment with lower airflows.