A1708 820-00840-a Keyboard not working

[flopper]

Got 00840-a here, came originally with jam filled keyboard, got new assembly, some (jam) marks around wifi, cleaned, reflowed.
Everything works except keyboard. Boots up, trackpad fine, wifi, sound etc.
Checked PP5V_S0, i am getting 5v there till i hear the dong(chime) from speakers and then fan stops and PP5V_S0 disappears from J4810 at least.
System still runs while fan is off.
Any idea? Much appreciated.

 

[2informaticos]

5V_S0 is also required by CPU power supply.
The board cannot work without this voltage.

 

[flopper]

yes, i understand that.
In PDF that is called PP5V_S0_KBD, in boardview just PP5V_S0. Pin 19/20 on J4810.
What could be cause of its disappearing from J4810?

 

[2informaticos]

Bad trace, or contact.
Must be present at pin 1 too.

 

[flopper]

I have only PP3V3_G3H_KBD present on J4810 after chime, nothing else.
Before chime all present. Fan stops spinning after chime.

 

[2informaticos]

5V_S0 remains present in other points?

 

[flopper]

when machines is powered on(open lid), 5V_S0 present everywhere, also Pin 1/19/20 of J4810, fan still not spinning. Last time i was checking with closed lid.
I noticed if i hold multimeter on pin 1 for like 1-2 minutes, 5V_S0 vill go to 2v-1v-4v-0v and then again to 5v in that time at least once (but its might be my hand shaking)
Turn on button still works on keyboard, caps lock does not.

J4810 when machine is powered on(login screen):
Pin1: 5.1v
Pin2: 0v
Pin3: 3.15v
Pin5: 3.35v
Pin6: 0v
Pin7: 0v
Pin8: 0v
Pin9: 0v
Pin10: 3.29v
Pin11: 0v
Pin12: 2.67v
Pin13: 3.12v
Pin14: 2.67v
Pin15: 3.39v
Pin18: 3.29v
Pin19: 5.1v
Pin20: 5.1v

Before chime, when fan spins for 30sec, i am getting 0.72v on Pin2, after chime, goes away.
But still nothing on Pin 6-9 and 11.

 

[2informaticos]

So 5V_S0 is steady, even on J4810?
I don't understand why did you measure there with closed lid.
When the lid is closed, S0 state is disabled and machine goes to S3.

Do not expect high voltage on pin 6, that will reset the machine.
KB communicates with PCH through TP.
If TP works good, then try another trackpad, or check its cable and connector.

 

[flopper]

i have tried MBL in new assembly, exactly same behavior.
TP works fine in both of them.
What will cause fan to stop after chime?

 

[2informaticos]

The fan doesn't run all the time in these boards.

 

[flopper]

when board is on, i am getting 3.3v on PP3V3_S4 on the J4810, when i check on the keyboard side same line it is 1.62v, should it be like this?
it does not give me a short, diode mode read is 0.434v, when flex is out there is continuity between pins, when flex is in there is no continuity but high reading 1740.

 

[2informaticos]

Bad connections, caused by corrosion.
Clean both connectors and check continuity from one side of flex over the pins of each connector.

 

[flopper]

Solved!
Bad J4810 on MBL, replaced, working fine now.
Thanks for your input.