A1708 no power, 5V 0.02A

[LozinMust]

Hello everyone,

I have an A1708 MacBook Pro that is not powering on. It stays at 5V and fluctuates between 0.02A and 0A. I've measured around the board and found that PP1V_S5G and PPVCCPCH_S5G are shorting. From visual inspection I couldn't find anything suspicious on those lines, so I tried voltage injection but I couldn't feel anything getting hot. Does anyone have any suggestions on what could be wrong with this board? Sorry in advance for being a noob, but I'm still learning. Hopefully someone in here can help me fix this issue.

[mon2]

Re: A1708 no power, 5V 0.02A

What and where did you inject?

Very possible that the PCH / CPU is heating up but the heat is being dissipated by the heatsink.

With the power delivery at 5 volts, the cd321x devices need to be reviewed first. Each must be working to dial up the 20v contract from the power adapter.

Review the article by @Piernov on how the 20v process functions.

http://logi.wiki/index.php/CD3215_Bootup_Sequence

[LozinMust]

Re: A1708 no power, 5V 0.02A

Thanks for the help! I injected 0.8V at 3.5A on the C8071 cap. I will follow the guide on the boot up sequence and see if I can find why I'm not getting 5V.

[LozinMust]

Re: A1708 no power, 5V 0.02A

Hello again, I finally had time to come back to this and made some progress.

As suggested, I followed the guide on the bootup sequence and found that the 1.1V were not present on PP1V1_UPC_XB_LDO_BMC. After looking closer at the TBT ROM chip, I noticed that there was some minor corrosion on it, which I cleaned with some IPA. Now I'm getting 20V in, so I think I'm back to the problem I originally noticed. I checked the two coils again (L7900 and L8060) and they're still both shorting to ground. I'm really not sure how to proceed from here, so any help will be much appreciated!

[mon2]

Re: A1708 no power, 5V 0.02A

Both of the linked inductors are for low voltage rails to power the PCH / CPU. Respectively, by design, each of these power rails will be of a low resistance.

For now, they are not of a concern. Best if you remove all power and measure the resistance to ground of each of these points. Post each resistance measurement.

Based on your progress up to this point, can you confirm the power delivery voltage and current? Are you now @ 20V and some current draw?

What is the voltage to ground of PPBUS_G3H @ F7000 ?

[LozinMust]

Re: A1708 no power, 5V 0.02A

Thanks for the help, mon2.

With power disconnected, the two inductors are dead short to ground (~0.4 Ohm on my meter). I worry that a dead CPU might be the problem because these indcuters are not linked to much on the board, but hopefully not.

Yes, I can confirm that the input is now 20V and, with nothing plugged in to the board, the power draw is 50mA (although when I first plugged in the cable it momentarily reached 1.1A but couldn't reproduce it again afterwards). On the fuse, the PPBUS_G3H rail is measuring at 13.1V.

[LozinMust]

Re: A1708 no power, 5V 0.02A

Just updating to say that I tried voltage injection again on the C8071 cap at 0.8V and 3.5A but this time I removed the heat sink. The PCH die got very hot, so it is most certainly dead and a no fix. Regardless, I'd like to thank you for the help!