820-00281-A Critical Software Update failed to install

it-solve

Member
Passes all Apple diagnostic tests. Geniuses said its a faulty TouchBar
Tried most of these - https://repair.wiki/w/A1706_2016-2017_13”_Touchbar_MacBook_Pro
  • Disconnected the Touchbar as it was showing only yellowish background
  • Wiped the drive and reinstalled High Sierra - It installed properly, but on the next restart this error comes again
  • Boot in Safe mode and tried to update from there. Takes a very long time to load into. Even the screen refreshes on lines. On the next restart went to the same screen
  • Disconnected LCD and tried on external to update, same error.
  • No visible corrosion around PP1V8_Sleep3_Buck3 = 1.79v
Any other suggestions?
 
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2informaticos

Administrator
Staff member
"Tried most of these"
You didn't mention if tried known good touchbar.

Check all resistors around U3900/10.
PMU_TO_SOC_RESET_L goes high?
 

it-solve

Member
PMU_TO_SOC_RESET_L Goes 1.79V when it turns on

Tried another touchbar, stuck at the same message, however no light on the brand new and used touchbar with a case. Suspecting something touchbar related on the board?

Resistors seems fine. Slight oxidation around underfilled SSD chips shield and test points. But nothing major, cleaned still same. Loads under Linux and Windows with touchbar disconnected,
 
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it-solve

Member
dont have spare A1770 for test, but have spare palmrest with functioning touchbar, as well as brand new touchbars
 

it-solve

Member
Got a spare A1707, placed this board into spare casing and same error message.
Placed working A1707 in this one's case and touchbar and everything else is working.

Any areas I should cross-compare measurements of while I have them both here? u3900 is shielded but will take measurements of the surroundings
 

it-solve

Member
@tcampbell34 Have you come across a crashed software update issue? It must have overheated and cold jointed then. Thanks for this I will try.
 
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it-solve

Member
1651563669998.png

Managed to measure these, but cant the rest, impossible without ripping the trackpad cables. This board also doesnt turn on without a battery.

J4401 Diode mode reading between two boards are identical on J4401
 

2informaticos

Administrator
Staff member
You should search and find test points, or component terminals connected to the lines of the connector.
 
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