Webcam not recognized on otherwise functional 820-4924 board.

[bjf]

I have a 2015 Retina 13" board that's working completely fine except it does not recognize the webcam. All ports (USB, SD Card, Thunderbolt, etc. are working.) There was a little bit of corrosion in multiple spots. There was a very small amount near the webcam connector, but the pins look completely unaffected. I've tried multiple webcams with no change. I've tested all voltages and found none only PP0V675_CAM_VREF missing. Does anyone know how this is created? It seems like it's coming from U3900. Maybe U3900 was damaged or I'm missing a signal that triggers PP0V675_CAM_VREF? On a known good board, PP0V675_CAM_VREF is on as soon as the board gets power. No webcam needs to be plugged in. Any thoughts would be greatly appreciated.

 

[dukefawks]

First test pins 1-6 on diode mode of cam connector.

 

[bjf]

Ok, so I replaced U3900, PP0V675_CAM_VREF is present now and the camera is recognized but there is no image and the green light is just blinking steadily.
Pins 1-6 (with cable plugged in:

1 0
2 0.377
3 0.377
4 0
5 0.379
6 0.378

Also, instead of being in the 0.275 range in diode mode, PP1V2_CAM is around 0.029. It's still producing 1.194 volts though. I put some voltage through it but can't find any obvious shorts or issues.

 

[dukefawks]

As far as I can see that 1V2 is generated by U3900 and goes nowhere else. I'd say U3900 was dead or you killed it while soldering.
Also did you try with a know good camera, could also very well be that the cam in the LCD is dead.