A2251 820-01949 No Power

[LugNuts]

Hello, I have an 820-01949 Macbook Pro that has MAJOR liquid damage. Luckily, the CPU and T2 seemed to have dodged it somehow. Initially, it only got 5v on the charger but I replaced U7000 and now I get 20v but not consistently, though generally if I just let it sit for a few minutes it goes to 20v. Still going through and fixing pads so it could just be a poor connection somewhere. I don't have much experience with T2 models but luckily it seems they are basically the same as non-T2 USB-C model. I ran it through my ultrasonic cleaner to help clean up the board.

Input: 20v 0.00-0.01 (completely dead)

PPBUS: 12.35v
PP3v3_G3H: 0.98v (not sure how CD3217 is negotiating 20v, runs off PP3v3_G3S maybe?)
PP3v3_G3S: 3.4v
PP5v_g3s: 0v

I have already replaced:
U7000
U7650
U6903
U7660 (gets 12v but only outputs 0.98v even after replacement)

Not sure where I should go on this one, luckily it's a personal board for learning more about T2 models so its not a rush.


Thanks for any help!

[Slam!]

Re: A2251 820-01949 No Power

PPBUS_G3H with 12.3 V usually indication something wrong with T2. If you have another Macbook you can invoke DFU mode and Revive (saves data) or Restore (wipes data). If you cant get into DFU mode then the rails associated with T2 chip will need to be restored before trouble shooting ppbus line.

[LugNuts]

Re: A2251 820-01949 No Power

Yeah, tried DFU mode and got nothing. Guess I need to dive into the schematics for the T2, thanks for the tip. I'll update the thread with any more information as I go in case others have a similar issue in the future. Any extra pointers you may have about T2 would be great, normally only work on non T2 MacBooks and trying to learn the new process.

Thanks!

[mon2]

Re: A2251 820-01949 No Power

PP3v3_G3H: 0.98v

Remove all power. Meter in resistance scale.

Measure the resistance to ground of L7660, pin # 1.

[LugNuts]

Re: A2251 820-01949 No Power

Looks like its getting ~100k ohms to ground

[LugNuts]

Re: A2251 820-01949 No Power

Took measurements from a working 820-00850 and get ~120k to ground on pin 1 L7660, not sure if that helps or not.

[mon2]

Re: A2251 820-01949 No Power

Resistance is ok.

Do the LDO rails work ok for U7650 ?

PP5V_S5_LDO

P5VP3V3_VREG3

Voltage of P3V3G3H_EN_R ?

[LugNuts]

Re: A2251 820-01949 No Power

Well, this board just doesn't want to get fixed now it's back to being stuck at 5v 0.00a.

PP3v3_G3H is 0v
PP3v3_G3H_RTC 0v

Not getting PPVIN_G3H_P3V3G3HRTC for U6903. Guess I'm really getting my practice in on this one.

[mon2]

Re: A2251 820-01949 No Power

Not at my desk and about to watch some NBA but check how far the 5 volt travels. Confirm if the usb fuses are in tact or are they blown.

How are you measuring the current? We own 2 different usb-c meters. The expensive one can show even small current like 30mA draw. The cheap one for the same case study will show 0mA draw.

[LugNuts]

Re: A2251 820-01949 No Power

No worries, thanks for all your help so far. I am using a "Keweisi KWS-1802C" bought from Louis Rossmanns store. In the past its been able to show small amperage.

I'll post some updates tomorrow.

[LugNuts]

Re: A2251 820-01949 No Power

Well, I made a mistake. I rebuilt the whole U7000 area as it was totaled from corrosion and when I put new resistors on for R7015 I had it positioned the wrong way. CHGR_AUX_DET wasn't getting PPDCIN_G3H and was just connecting back to itself and only just noticed that when looking at the boardview and schematics.

Fixed that and now the charger is going nearly instantly to 20v 0.00a 100% of the time.

Current readings:

PPBUS_G3H: 12.35v
PP3v3_G3H: 0.98v
PP3v3_G3H_RTC: 3.4v

Now for what you asked for earlier:

PP5v_S5_LDO: 0v
P5VP3V3_VREG3: 3.3v
P3V3G3H_EN_R: 0v

Extra Readings From U7650
P5V_P3v3G3H_LDO_EN: 0v
PPVIN_G3H_P3v3G3H: 12.35v

I'll keep messing around with it tomorrow, I hope this isn't an issue with a broken T2

[LugNuts]

Re: A2251 820-01949 No Power

Got it to start powering up!

I was looking through the schematics and boardview, found a resistor "R8050" that delivers PPBUS_G3H to PMU_VDD_HI. From what I understand now that I got it working (almost) is that T2 has something to do with creating PP3v3_G3H, not like the old non T2 boards that had a dedicated IC for that.

New Readings:
PPBUS_G3H: 12.6v (was 12.3 due to bad resistor "R8050" and T2 boosted PPBUS to 12.6v)
PP3v3_G3H: 3.4v (I was trying to find this source for so long when it was stuck 1v)

Now the board gets 20v and starts some sort of boot process, T2 turns on, smaller die on CPU warms up (no noticeable heat, seen through thermal cam)

Goes 20v 0.06a then climbs to 20v 0.35-0.40a while T2 and CPU do something then it drops back down to 20v 0.06a. Maybe SSD rail isn't working or another rail is having issues on start. I am just glad to have some sort of progress on this and wanted to post an update for anyone who may have a similar issue in the future.

[smith.rja]

Re: A2251 820-01949 No Power

Hey LugNuts!

have the exact same boot process as you. 20v up to ~300ma before dropping to ~65ma and nothing.

Boots to DFU and revives/restores without error but same boot issue. did you get anywhere?

[VRauza]

Re: A2251 820-01949 No Power

Had similar issue on A2551, it was charging battery and could enter DFU mode but no boot. Turned out to be corrosion on R7441 pin 1 which is PP1V8_S5. Not sure how any liquid got there as it is under a protective tape and there were zero signs of liquid anywhere else on the board.

[nelusab]

Re: A2251 820-01949 No Power

Hi is somebody so kind to help me with an soc rom bin file , a genuine one dumped from a working A2251, for reflashing t2 bios soc rom chip?

[nelusab]

Re: A2251 820-01949 No Power

I have the same problem and a tehnician told me that is about a corrupt bios.