820-00923 - Voltage on U3200 fluctuating but U3100 is stable.

[bjf]

This board had corrosion mainly around U3100 and U3200. If I plug into the top USB-C port the board will get 20V and turn on normally. If I plug into the bottom port the voltage on U3200 fluctuates from 0V up 5V and right back down. So F3001 goes up and down. PP3V3_G3H also goes up and down from 0V to 3.4V. PP3V3_UPC_XB_LDO also goes up and down. I've replaced everything that looked bad. I can't find any shorts. I'm guessing I might be to the point of having to replace U3200. But also wondering if I should, or can, just leave it alone and not use the bottom USB-C port.

 

[2informaticos]

Check resistance to ground on all LDO outputs of U3200.
Do all these voltages try to appear?
Compare with U3100...

 

[JohnB8812]

Just making sure you've tried a new USBC Port? They are connected I'm pretty sure, and I know if one of the ports is bad, it will cause this. If you have, likely an issue near U3200 if not the chip

 

[bjf]

Ok, so I pulled the new C3208 capacitor I put on because this wasn't happening with the old burnt out one and I wanted to see if that might help. I was measuring around 3KOhms to ground. Without C3208 on at all the board turned on. And yes, all the voltages were coming up and down including the LDO voltage. I replaced C3208 again and the board is working. My replacement C3208 must have been damaged in the soldering process. It's a little messy because I was avoiding using hot air to attach the new one so it might have gotten burnt out internally. Thanks for the tips.