MacBook Air 820-3435 no power?

[Im_JackJohnson]

Good Evening,

I come to you in a time of great need, I am looking for some help with diagnosing this 820-3435 MacBook Air.

It has suffered some liquid damage but the board was cleaned before I got my hands on it, so I can't see anything too obvious.

There is a faint green light on the charger, I've been taking this as no light. I'm using a genuine 85W magsafe. Replacement DC in board on the way.

Some voltages:
PPBUS_G3H 8.6v
PPBUS_S5_HS_COMPUTING_ISNS 8.6v
PP3V42_G3H 3.42v
PP5V_S5 3.8-5v (pulse)
PP5V_S4RS3 0-400mv (pulse)
PP5V_S0 57-130mv (pulse)
PP3V3_S5 0-3.2v (pulse)
PP3V3_S4 0-40mv (pulse)
PP3V3_S3 0-100mv (pulse)
PP3V3_S0 70-130mv (pulse)

Some signals:
SMC_PM_G2_EN 0-3- 5v (pulse)
SMC_BC_ACOK 3.3v
SMC_ADAPTOR_EN (pulse)
SMC_RESET_L 3.3v

All of the things listed above are not shorted that I can tell anyway, they all have acceptable ohm readings.

I suspect this is a bad U7501, but I could be very wrong would someone be able to help be diagnose this correctly?

I am open to any questions, I may very well ask some really stupid ones in return, I apologize in advance

Jack.

[mon2]

Re: MacBook Air 820-3435 no power?

PP5V_S5 3.8-5v (pulse)

Remove all power. Meter in resistance mode.

Check the resistance to ground @U7501, pin # 29.

[Im_JackJohnson]

Re: MacBook Air 820-3435 no power?

Check the resistance to ground @U7501, pin # 29:

1.2m Ohm on pin 29.

[mon2]

Re: MacBook Air 820-3435 no power?

https://boards.rossmanngroup.com/thr...3-5-etc.27708/

[reformatt]

Re: MacBook Air 820-3435 no power?

Most multimeters aren't quick enough to properly measure rails during pulsing. A oscilloscope is often better for determining what a rail is rising to in this case.

That said, pulsing is often due to a missing (or shorted) rail in the power sequence. So check each coil on the board for shorts, and that includes the caps/coils above the CPU. Can also be a bad U6100/termination resistors as well, or a bad SMC or crap underneath it.

Are you getting PM_SLP_S4 going high at all? Seems you are if you have activity on your S3 rails etc.

[Im_JackJohnson]

Re: MacBook Air 820-3435 no power?

I've checked 3v3 rails, all showing the following:
PP3V3_S5 5k Ohm
PP3V3_S4 1.4m Ohm
PP3V3_SUS 26k Ohm
PP3V3_S3 1.1m Ohm
PP3V3_S0 1.1k Ohm
PP3V3_S4SW_SNS 1.1m Ohm
PP3V3_S0SW_SSD 202k Ohm
PP3V3_S4_TBTAPWR 500+k Ohm

I believe these are all good, PM_SLP_S4 is going high briefly and pulsing the same as MP_G2_EN.

Thank you for the link, it confirms my thoughts about u5701. I have some new TPS51980A's on the way, and I'll clean up the SMC.

I'll report back the results. Thank you all.