820-00850 board (A1989) with 3 of 4 USB-C ports functional

[sekidata]

This 820-00850 board has 3 of 4 ports at 20V. The remaining port (USBC_TA) cycles between 5V and 0V when plugged in one way, and remains unresponsive when plugged in the other way. I checked all relevant LDO and power lines and found no shorts. What component could cause this plug asymmetry?

 

[2informaticos]

Check CC1/2 lines (diode mode) and compare with other ports.

 

[sekidata]

CC1 and CC2 lines have the same diode mode readings as the other ports.

 

[2informaticos]

Compare diode mode readings between J3300 and JB500.
You should get something different for the port which doesn't work on both directions.

 

[sekidata]

Strangely, all pins on both connectors show exactly the same readings in diode mode. There was a small amount of liquid in the area around the CD3215s (UB400 and UB300) but no visible damage.

 

[2informaticos]

Which channel has the strange behavior?

 

[sekidata]

It's the TA channel. I could replace UB300 but I'd like to first know where the fault lies und understand the behavior.

 

[2informaticos]

Did you check CC1/2 lines in diode mode, on both sides of QB630/40?

 

[sekidata]

Yes, both sides of RB630/640 show the same diode mode readings as for the other 3 ports. I also checked on a separate board and they are the same, also.

 

[2informaticos]

Replace UB300, if you don't find any difference between channels.

 

[sekidata]

I replaced UB300 and that fixed this issue. I now have 20V on all 4 ports.