A2251 - 820-01949 - liquid damage, powers on, only external display, solid apple logo

[tawnytim]

This device came in as a liquid damage machine. There was very little corrosion on the board and all of it cleaned up very well. It appears to power up properly, drawing about 2.3A. If I let it sit long enough I get a couple of faint vertical lines on the screen but no picture. With LCD disconnected and using external display I get a black screen with the apple logo but nothing else. Caps lock toggles properly. I've never seen a MacBook just sit at the logo screen without eventually giving an error, but this one does.

Touchbar and keyboard BL not working.

Where should I check first? Or do we probably have fried memory or something?

 

[2informaticos]

Any liquid sign on J8500?
Check diode mode to ground on its EDP_INT lines.

What about U4802 signals (with lid open)?

 

[tawnytim]

No signs of liquid damage on J8500. All EDP_INT lines read ~.263V on diode mode. U4802 is on the bottom side of the board. How should I set this up for testing?

 

[2informaticos]

Check U4802 signals with board alone on the desk.
Nothing else can affect lid sensors; as they are placed on the MLB.

 

[tawnytim]

Sorry to sound dumb, but exactly what am I checking? Diode mode?

 

[2informaticos]

Voltage levels...

 

[tawnytim]

1.8V on all pins except the GND and UNCONNECTED

 

[2informaticos]

You should try known good LCD assembly.

 

[tawnytim]

That worked - thanks!!!