MacBook A1706 'Critical Update Required' 820-00239

[Panrix Microelectronix]

Hey Guys!

We've got a A1706 with touchbar that is failing to update. We've tried disconnecting the touchbar, front camera, updating with a different MacOS and still the same. I read somewhere to check U4200 and U3900 in case of any minor corrosion and these are pristine.

Also tested the board in a different housing and still the same error.

Not sure where to check next.

Just to add that the Macbook boots in safe mode as expected.

Any pointers would be much appreciated! Thank you

 

[2informaticos]

Any history available?
Did someone open it and changed something?

Can we get 820-xxxxx code of your board?
Is a "must post" in title...

 

[Panrix Microelectronix]

Apologies - the board number is 820-00239.

When we received it in the client just said it kept freezing and they were having trouble with the software reinstallation. Also the display had classic 'flex-gate' issues which we have repaired. No signs of liquid damage or any previous repairs.

 

[2informaticos]

So touchbar was working before reparing the flex-gate problem?
If you removed the board from shell, check for knocked off components, or broken traces.
Check all resistors near U3900.

 

[Panrix Microelectronix]

The Macbook was still in setup mode when we received it so we couldn't complete our normal diagnostics. Touch bar was not showing any activity during this stage (which is normal I believe).

Flex gate was completed without removing the full screen or logic board. I'll check the resistors and report back. Thank you!

 

[Panrix Microelectronix]

I've checked the resistors around U3900 and all are showing correct value - tested against known working board. no signs of any missing components

 

[2informaticos]

I faced this problem, with bad R3973, or R3990.

 

[Panrix Microelectronix]

Just to update that we replaced U3900 and the MacBook now boots up fine and touch bar works.

Thank you for your help!