820-00928 Critical update

No-Clean

Member
Clean board no liquid or rust to be found.

Not sure if there is a difference but when the board boots it ask to connect to network

Board alone connected to external monitor shows the problem, so I know this is board problem, I went thru the list here:
https://logi.wiki/index.php?title=Critical_Update_Required_Troubleshooting

I also installed clean OS and also installed combo update, but same problem.

I have checked all SSD lines, replaced the Power Manager chip U4200 and reflowed U3950 but nothing...
 
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No-Clean

Member
I've actually read most posts here including that one regarding this issue (I like the link I posted better as it goes into more details) but same result, I have also checked J4402, J4401 and J4900 for shorts and they are all good, now I need to test voltages for those connectors, but I wanted to reach out here just in case.
 

No-Clean

Member
Ok Im back with another one of this boards, same problem, this one had corrosion around U4200 and R4321, R5373, R4320 and R5372 were all corroded away, I replaced those with 0ohm resistors per the schematics and also put a known working U4200 chip.

U4200:2 3.4V
U4200:60 0V
U4200:6 0V
U4200:3 0V

Next I was going to reball U3900 but it has underfill and I am not sure if that is necessary.

Initially the board had fans running at max and the mac ran slow, now after the work I did I am stuck at critical update.
 

2informaticos

Administrator
Staff member
Can you use schematic notations, instead of boardview?
Is the normal way to reffer signals and voltages.

Re-check your job.
Be sure all resistors are needed.
Some of them can be optional; compare with other board.
 

No-Clean

Member
I just changed the answer to reflect the schematic notations.

Re-check and the 4 resistors match the 2 other boards I have, both in resistance and placement.
 

No-Clean

Member
J4402:1 DFR_TOUCH_PANEL_DETECT 0.2V
J4402:2 DFR_TOUCH_LID 0V
J4402:18 DFR_TOUCH_RESET_L 1.8V
J4402:20 PP1V8_S0SW_DFR 1.8V
J4402:21 PP1V8_S0SW_DFR 1.8V
J4402:22 PP5V_S0_T139 5.1V
 

No-Clean

Member
Just reballed U3900, what a beast of a reball. But got it done right, unfortunately I still have the same problem. Can this chip be replaced with another one from same board?
 

2informaticos

Administrator
Staff member
So this board has a good SSD?
Does it recognize it and start installation process?
If yes, then be very sure youve tried known good LCD and Touchbar assemblies.
 

No-Clean

Member
Yes good SSD because this used to boot into customers system but ran slow, now that I fixed the corrosion it is coming up with critical update error.

I now have also replaced U4200 carefully but same issue.
 
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No-Clean

Member
The problem I see is that bare board starts up but U4200 has no output on SOC_PMU_BUCK0_LX and SOC_PMU_BUCK3_LX when I boot board alone on a working board I do get those voltages, this is maybe the cause of critical update error.
 

2informaticos

Administrator
Staff member
If the board booted before into macOS, w/o critical error, then something happened when you've cleaned corrosion, or changed U4200.
Did you pick the chip from same model donor board?
 

No-Clean

Member
Critical update came up after cleaning corrosion and putting back corroded resistors, no IC chips were replaced at that point, I then replaced U4200 same result, then U3900 same result, both came from a 820-00281 board NOT 820-00928
 
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No-Clean

Member
Okay I just re-checked the work I did and replaced U3900 from a 928 board and reballed again U4200, checked for continuity on the traces I worked/replaced resistors but no change, I invested a lot of time on this board, I give up, so frustrated.
 
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