Chosen Solution
so to start out i dont specialize in mac repair, i mostly work on phones. but a friend of mine had an issue with their macbook so i figured id take a look at it. so everything is disconnected but the board and dc in board. it shows a green light on the charger and fan starts to spin up then stops. i checked all the main power rails and i found one that isnt right. pp5v_s3 is missing and its weird, when the fan starts to spin it shows 5volts for a split second the 0 again, and if i hook power to the board then disconnect power and test the line is shows as .006 voltage drop in diode mode but if u keep the multimeter probes on it starts to rise until its at like .400 i went over the entire board under a microscope many times and also looked at it with ir camera. i dont see anything that looks terrible. but im stumped and am hoping one of the experts on here can point me in the right direction.
You’ll need to spend sometime reviewing Louis Rossmann’s YouTube channel as he has documented a few different causes for your problem with a bad pp5v_s3. Get the schematics & board views so you can follow what he does and what trace or component needs to be repaired/replaced.
