A2338 MacBook Pro with dark touch bar

[sekidata]

This 2020 M1 machine came to me for battery replacement. Works fine now except I can't get the Touch Bar to turn on. The Touch Bar works fine with another logic board in the same topcase. I don't have the customer's password, but the Touch Bar should illuminate on the login screen, correct?

What's the fastest way to troubleshoot? I have only checked PP1V8_AWAKE_DFR and PP3V3_AWAKE_DFR so far.

 

[2informaticos]

I expect mechanical damage, caused in the battery replacement process.
Inspect near the screw holes and connectors.

Lost just backlight, or touch functions too?

 

[sekidata]

Inspection showed absolutely nothing. No touch function, no illumination.

 

[2informaticos]

Any error pops up starting in diagnostic mode?

Just in case, get the password...

 

[sekidata]

Aha. Just learned something I did not know. When FileVault (Disc encryption) is on, the Touch Bar remains completely dark until after the password is entered. Same for Diagnostics and Guest Mode. I verified this using an identical machine set to my account. So your hint was spot-on: get the password and everything works now.

 

[2informaticos]

I forgot about FileVault.
When is enabled, the drivers aren't loaded until password is inserted.