820-3437 keyboard & trackpad not working light liquid damage

[Glenn]

Have this Macbook air 820-3437 with no working keyboard and trackpad. board is light liquid damage.
Have tray a know good trackpad, keyboard and cable but still not working.

measurement on j4800:
Pin 19: 3,4V
Pin 14: 5,15V
Pin 10: 2,13V

R4830 2.09V and 0,1Ω diode mode give 0.367

Have test with a usb bluetooth mouse and that work

will test if it work when pressing down options button when startup.Nothing happens when pressing options button at startup just booting as normal.

 

[aprendiz]

Corrosion under J4800 or leaking C4800 ....

 

[dukefawks]

No, that would fry R4830.

Is there 3V on R8050? If not check 3V on R5294 pin 1 (yes it is not on the board but test that pin)

 

[Glenn]

R8050 Pin 1 give 3,34V and 0.2Ω
R5294 Pin 1 give 3.41V

 

[dukefawks]

So, 3V present at R8050 and not at R4830. They are on the same rail, there is your problem.

 

[Glenn]

Could it bee a bad chip between this? Bade trace? Should i run a wire from r8050 too r4830?

 

[XooP]

Duke: Are you sure, don't you mean R8000 and not R8050?

R8050 is the PP3V3_S4SW_SNS
R8000 is the PP3V3_S4 Rail

 

[XooP]

My guess is something wrong with U8000 or R8000

 

[Glenn]

C8000 give me 3.3V and R8000 give me 2.13V

 

[XooP]

It may also be something wrong after R4830, if you remove it and you get 3.3V you know where to look. C4800 or trackpad connector next.

 

[Glenn]

Thank you XooP. will remove R4830 and check. report after

 

[XooP]

There may be other places where the voltage on the rail can be pulled down, but you need to start somewhere

 

[dukefawks]

Yeah I meant R8000.

If S4_PWR_EN is present then it could be short on the bus or dead U8000.