820-00239 tpad/kbd not working and questionmark folder

[ytesfay80]

Hi, This touchbar macbook originally had liquid damage only around the U3100 area. I had to run a couple wires on a resistor and capacitor due to the pads being gone on them. After that the machine turned on and everything worked fine. I sent it back to the customer and now they sent it back to me since it is showing a questionmark folder and now I don't feel the trackpad clicking and even if I hold the option key on startup nothing happens.
This isn't the first time I've fixed a machine that had liquid damage around a USB-C controller chip only to have it return back a few weeks later for a questionmark folder appearing but this one doesn't make sense to me because the only liquid damage was on the opposite side of where the SSD controller chip is.

Here are some measurements around the TPAD area that I took to find out why it's not clicking.
F4500 - 13v on both sides.
L4500 - 5v on both sides
PP3V3_S4_TPAD - 0.08v

 

[2informaticos]

"PP3V3_S4_TPAD - 0.08v"
Check for short there, w/ and w/o trackpad flex connected.
If OK, then check continuity to R5650.
Do you get correct PP3V3_S4?

 

[ytesfay80]

Okay I just measured for a short and yes PP3v3_s4 is 0v to ground in diode mode with and without the trackpad being plugged in. In voltage mode I was also getting 0v on PP5V_S4 but in diode mode PP5V_S4 is not shorted to ground. PP3v3_S5 is present and working fine.

Should I start injecting voltage on PP3V3_S4 to find the short?

 

[2informaticos]

Yes, try that.
Remember my advices about voltage injection...

 

[ytesfay80]

I'm not sure where your advice on voltage injection is but could you let me know what you recommend for this?

 

[2informaticos]

Always start injecting lower voltage.
Increase it, but maintain ampers bellow current limit of the power supply.
Never inject more than 120% of the nominal voltage of that power rail.

 

[ytesfay80]

Okay I injected voltage and found that is was C3736 that was shorted to ground. I replaced that and everything is working fine now.

Thanks!