MBA 820-01521 - keeps restarting

[Mrsina77]

Hi,

my macbook air 2018 (A1932) keeps restarting. I have found that lot of caps are shorted around U7800.
(C7814, C7835, C7833, C7815, C7828, C7813, C7827, C7812, C7811, C7823, C7826, C7821, C78C0, C7822, C7824, C7825, C7837, C7834, C7836, C7838) - PPVDDCPU_AWAKE and PP0V82_SLPDDR

Are these caps low resistance or U7800 should be inner shorted? MBA was water damaged but after the clean MBA worked about 10 times but after that keeps restarting after few seconds.

Water damage was aroung Q7680, Q7660, Q7030 and Q7040. I will try next week to replace these mosfets but I dont thinks that it will help.

Thermal cam show some heat aroung U7210 and L7210. I have tried to inject 1V to the L7210 but no short anywhere.

btw: PP5V_G3S voltage falls to 0V during the restart.

Thanks for any help.

[mon2]

Re: MBA 820-01521 - keeps restarting

Yes, low voltage rails will always have low resistance power rails.

If you are able to power up with video at all, then the CPU is working.

What is the voltage to ground of P5VG3S_EN_DLY ?

Remove all power -> meter in resistance mode.

What is the resistance to ground of PP5V_G3S ?

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

Yes, low voltage rails will always have low resistance power rails.

If you are able to power up with video at all, then the CPU is working.

What is the voltage to ground of P5VG3S_EN_DLY ?

Remove all power -> meter in resistance mode.

What is the resistance to ground of PP5V_G3S ?

P5VG3S_EN_DLY is stable 3,31V

PP5V_G3S i hard to measure. Lot of changes from kohm to Mohm. But after two minutes on one pin it shows about 40kohm.

[mon2]

Re: MBA 820-01521 - keeps restarting

Do you see the 3v3 on P5VG3S_EN_DLY even when PP5V_G3S is OFF = 0v ?

PP5V_G3S i hard to measure. Lot of changes from kohm to Mohm. But after two minutes on one pin it shows about 40kohm.

That is ok - we know now that this rail is not shorted.

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

It drops at the same time.
When I plug the power cable after 10s fan starts spin for 3s. After that it stops and after next 10s it starts spin again for 8s and after that both voltages drops for 5s. After that voltages are present again.

[mon2]

Re: MBA 820-01521 - keeps restarting

You have power cycling.

Review this thread to see if it helps.

https://boards.rossmanngroup.com/thr...and-low.60907/

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

But it was working fines for about few time after clean. AUX board was water damaged too and battery board too. Everyting was cleaned but I disconnected it. All what was connected was display and battery but somehow it started cycling. You think that U7800 can be somehow damaged?

[mon2]

Re: MBA 820-01521 - keeps restarting

Is it stable with only the adapter? (No battery)

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

I am testing it only with adapter.
I remember that when the trackpad was pluged in (it was too water damaged I just remember) MBA did not want to start up and there was too power cycling (restarting MBA). After unpluging the MBA loaded fine. After pluging in again power cycling. Maybe some short on trackpad railways?

[mon2]

Re: MBA 820-01521 - keeps restarting

Disconnect the trackpad and keyboard. Use the power button @ SWE010 on the logic board to turn the board ON / OFF.

Test again without the trackpad / keyboard. Perhaps the I2C / SMBUS interface lines are being strapped down and causing this recyling of the power.

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

Voltage is 1.8V on both resistors but voltage drops to 0V like PP5V_G3S.
I have tried to turn on/off with SWE010. Current to the MBA was higher up to 0.45A. Stable current from adapter is about 0.2A. Firstly the second spin was longer about 2sec and fan went to very high speed and then it turned off.

[mon2]

Re: MBA 820-01521 - keeps restarting

What is the voltage to ground of PPBUS_G3H ?

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

It 12.67 without battery.
11.77 with battery.
I have tried to use thermal cam with battery connected and there is one hot area at its L7030. Its about 53C immediately.

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

There is the photo. It is only when battery is pluged in. This place was water damaged. It does not looks so nice but all caps around this is good.
With battery it drains up to 1.5A.

btw: PPBUS_G3H drops same like PP5V_G3S for few seconds.

[mon2]

Re: MBA 820-01521 - keeps restarting

Remove all power -> measure the resistance to ground of L7030.

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

1. Pin is 6,25Mohm
2. Pin is 6,50Mohm

[mon2]

Re: MBA 820-01521 - keeps restarting

Ok readings.

Remove all power. Meter in DIODE mode.

Red meter lead, yes RED to GROUND.

Black meter lead to the point to measure.

Measure the DIODE reading for:

DP_INT_AUXCH_C_N
DP_INT_AUXCH_C_P

What is the measurement for each point of interest?

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

Its 0.257 for both.

[mon2]

Re: MBA 820-01521 - keeps restarting

Then there is hope. If the readings were not the same, the CPU is dead - according to the earlier linked thread from Louis' forum.

Can you try to see if the logic board is seen under DFU mode ? Personally have not done this (yet).

[Mrsina77]

Re: MBA 820-01521 - keeps restarting

I was not able to get into the DFU mode because when the trackpad/keyboard cable it pluged in the MBA restarts faster so I am not able to get into the DFU. Am I able to get into DFU with external keyboard (not from apple)