820-00840 one port stuck at 5v

[tcampbell34]

Hello. I got a 820-00840 in that had some minor liquid damage and corrosion around the backlight output caps and the CD3215 chips. When I plugged in the app meter, it would not even turn on for either port. Found short on PP20V_USBC_XA_VBUS so I replaced U3100 and the short was gone. Now when I connect the charger to the port for U3200, it goes to 20v 0.60a, but the port for U3100 stays at 5v 0.01a and PP3V3_G3H is 0v when using this port only. PP3V3_G3H is 3.3v when connected to the other port so not sure what is happening. I have replaced U3100 3 times now with the same result each time so U3100 is not the issue. It seems like PP3V3_G3H is being shorted to ground whenever I used the usb port for U3100, but it measures .329 in diode mode. Any idea what could cause this?

 

[2informaticos]

Use the logic; you cannot have short on a rail where you get voltage from other port!

Non-working port doesn't open input MOSFET probably.
Replace that MOSFET, but check its series coil first.

 

[tcampbell34]

Sorry which MOSFET should I replace? There was some corrosion around Q3350, Q3360, and Q3351. I replaced all 3 but no change.

 

[2informaticos]

Q3100 is the corresponding MOSFET of U3100.
Be sure first it gets 5V on the input; check fuse and coil.
You can bypass it IN-OUT, only for test...

 

[tcampbell34]

Yea that was it. I changed Q3100 and now I got 20v on both ports and the board boots. Thanks for the help.