MacBook Pro A1990 EMC 3359 820-01814-01 no power

[bpcmr]

When plugged in it stays at 5v

I don't know what caused the issue but on removing the mobo I saw some corrosion (pictured). This picture was taken after I tried to clean it but it's still hazy looking.

I checked for shorts in the nearby area

C3501 pin1: 58Kohm
CC749, CC797, and CC796 pin one read about .8ohm

pin 2 on F7000 and F7001 read about 2.2ohm

still very much a newbie so any advice on common faults I should check for would be helpful, thanks

[mon2]

Use ipa (alcohol) - Costco pharmacy grade is excellent to clean up this area.

[reformatt]

Dead A1990/A2141 I immediately check for simultaneous shorts on PPBUS_G3H and either of the PP2V5 NAND power rails. TPS61280 failure is pretty common (U9080/U9580). This TI IC has killed many a Macbook over the years by pumping 12V straight into their SSD's. In true Apple fashion, they repeat the same Engineering mistakes over and over again, and they are still using this IC on the latest M4 Mac Mini removable SSD's. Built in obsolescence at it's finest.

With any luck, you just have a PPBUS short, and it's a decoupling cap on one of the chicken wings. Most common on A1990 is C9081.

I did have one recently where C9081 was corroded and shorted but it had created a high resistance connection on the pad to PPBUS_G3H_SSD0_SNS. As a result, the few extra ohms of this bad connection were not enough to shut down the main power rail and it sat there burning away until carbonised the PCB underneath and shorted PPBUS_G3H directly in the PCB itself. Had to write that one off as all the SSD rails were shorted to ground in the PCB just because of this stupid cap.

[bpcmr]

So I've checked components leading into and out of U9080
C9081 pin one showing 2.2 ohms and C9091 pin 1 is 4ohm

pp2v5_nand_ssd1 seems empty. Mostly just pads
PP2v5_nand_ssd0 I've checked a lot of components on this line and which have this as an output and nothing has shown under 0.3ohm

I've also checked components that have ppbus_g3h as an output and no shorts, closest I found was C6470 pin one reading about .8ohm.

should I be more thorough in checking PPBUS_G3H or is there another rail I should be looking

i did clean the area mon2 pointed out.

I will try putting it back in and seeing if cleaning the corrosion fixed anything

[reformatt]

4 ohms on C9091 isn't good, that's your SSD 2.5V power rail. Usually if it's one of the decoupling caps (C9089 etc), it will read dead short. Non zero is often a NAND that's failed due to the overvoltage from the failed TPS61280 (can be one or more, or all of them). Remove U9080 and see if your PPBUS_G3H short is removed. Alternatively, use 1V voltage injection and thermal camera if you have one to pinpoint the issue.

BTW, the NAND's are combined in a RAID 0 stripe by the T2, so data definitely gone when this happens.