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Okay, I've gone back through checking the rails... PP3v3_S4 boosts twice the same as every other S4 onwards rail, but after the others boost twice, they drop to 0v. PP3v3_S4 drops to 0.45v and sits there.
The damage was in the U3210 area, so I swapped out U3210 to see if it made a difference...
We use this stuff in 0.038mm or 0.51mm dia (depending on stock) its 60/40 solder with 1.1% no clean flux core.... not that you wouldn't clean after anyway :)
Comes as a 500G reel so should last a fair while.
Without the bios, its boosting PM_SLP_S4_L and VCORE in stages by the looks of it. So it boosts after every 2 second pause and changes the voltage up or down each time in a cycle.
VCORE = 0.08v (pause) 0.12v (pause) 0.24v (pause) 0.53v (pause) 1.1v (pause) 1.3v (pause) then does the same in...
Nothing obvious near the cpu at all. To be honest, apart from the backlight chip, there wasn’t much anywhere.
Do you mean if remove the bios chip entirely and then connect the MagSafe, it should power cycle constantly?