MacBook A2179 water damage, probably bad T2

[baglaivlad]

Hi everyone. First of all, repairing stuff is my hobby so sorry if I ask dumb questions.

I got a water damaged A2179. Audioboard was seriously damaged and connector shorted. Got 5V on charger. CD3215 are OK, as far as I can tell. The only places with corrosion are audioboard and Q7065 (which I believe is responsible for battery charging and not so interesting as of now).

Followed up bootup sequence from here: https://repair.wiki/w/A2179_2020_MacBook_Air. Found that I have neither of voltages from PMIC (U7800), but no lines shorted

Replaced PMIC (U7800), now I have all the voltages. PPBUS_G3H is like 12.3V (a little bit low), PP3V_G3H is 3V, but PP5V_G3S is 0V (as well as all following voltages in bootup sequence). PP5VG3S is also missing (0V).

Got 5V (0.02A - 0.40A) looping on the voltmeter. Sometimes it requests 20V from the charger, but immediately steps back to 5V. Have a hot spot on T2 chip in moments when consuming 5V 0.40A from the charger.

Measured audio board connector (J6100) and found that SPKRAMP_INT_L and SPKRAMP_RESEL_L lines have 10 Ohm resistance (not kOhm), almost shorted to ground.

Injected 1.8V into SPKRAMP_INT_L line. The only hot spot is T2 chip.

So here are my questions:
1. Can we say with confidence that the T2 chip is fried?
2. Can I replace T2 chip from other iCloud locked MB from the same model (along with TouchID button)? Or it will get this laptop iCloud locked as well?

Tried to google info about replacing T2 chip, but only stumbled upon "iCloud removal" scams. Looking forward for your help guys. Thank you

[reformatt]

Re: MacBook A2179 water damage, probably bad T2

See if it's detected in DFU first. T2 needs to load bridge OS before those later voltages come up, and bridge OS is on the NAND's. DFU will tell you more about what is going on here. NAND's need to be working with a valid bridge OS first so you need to rule all that out. You don't get to the Intel power sequence till T2 is working.

AFAIK, iCloud is linked to the T2 itself, so taking it off an iCloud locked board is of no help. Also T2, you need to be mindful of the RAM on top of the main IC as well which is problematic if there is underfill on the chip. It's like an iPhone CPU essentially.

[baglaivlad]

Re: MacBook A2179 water damage, probably bad T2

Thanks for your response! I tried to connect it to another MacBook (Air 2018 to be specific) through Apple Configurator, but it does not detect it as a device. Occasionally host MacBook showed "This thunderbolt device is not supported" (or so) pop-up. But nothing comes up in Apple Configurator. I tried to connect it using Apple Type-C cable that comes with the MacBook, btw.

My thought it is not in DFU mode, because of looping Amps reading on voltage meter and looping voltages from PMIC. PMIC voltages are up then a moment later is down a bit (like something pulls the voltages down), and then again. Looks like it tries to start but then failed and tries again. The only hot spots are T2 chip and PMIC (actually not hot, but I can see temp difference through the thermal camera).

Sadly T2 is tight to iCloud status, it's a bummer. I think I should look for non-locked, but non-working MB, the same model (the same RAM/SSD?). Luckily, no underfill under the T2 on this model, so it looks like it can be easily removed from the donor board.

[piernov]

Re: MacBook A2179 water damage, probably bad T2

Got 5V (0.02A - 0.40A) looping on the voltmeter. Sometimes it requests 20V from the charger, but immediately steps back to 5V. Have a hot spot on T2 chip in moments when consuming 5V 0.40A from the charger.

One corner of T2 is expected to get warm during its boot process, not necessarily an issue.

Measured audio board connector (J6100) and found that SPKRAMP_INT_L and SPKRAMP_RESEL_L lines have 10 Ohm resistance (not kOhm), almost shorted to ground.

That's an issue however, common on this board in case of liquid damage, PPBUS_G3H gets sent to SPKRAMP_RESET_L. Sometimes you only lose audio, sometimes it's worse, but in any case T2 is damaged.

Be mindful that T2 has 2GB RAM on >=1TB SSD boards and 1GB RAM on <=512GB SSD boards.

[baglaivlad]

Re: MacBook A2179 water damage, probably bad T2

Thanks for your input!

Considering T2 chip replacement. I think I found the donor board and may try to do a T2 swap soon. I wonder, what will happen with the laptop's serial number after T2 replacement? Will it stay the same of will be transferred from the donor laptop along with T2 chip?

As far as I know, MB serial number are stored in EFI chip. At least this serial number is showed in "About this Mac" dialog. But T2 chip stores some iCloud activation data. Should EFI chip be swapped from the donor as well?

What (if any) side effects will T2 replacement make? Can the laptop be updated in the future with out any problems? Can it be used as usual? Can't find the precise information about T2 replacement. Thank you!