USBC Power (again) 820-00840

[acowan]

Well, I thought I had the USB-C power negotiation sorted .. It seems not.

So I have an 820-00840 with no power.

PPBUS_G3H 0v
UPC_XB_GATE1 = 0v
UPC_XB_GATE2 = 4.9v

Now, why is the voltage at gate1 0 ?? How the hell does this USBC controller work

 

[acowan]

R3203 - schematic says 15k/ NEED 0.1% - measures 12k
R3103 - schematic says 15k/NEED 0.1% - measures 8k

Are these actually critical?? It seems unlikely

 

[2informaticos]

Why do you expect to get nominal value of a resistor measued onboard???

Check voltage and diode mode on ALL LDO outputs of CD3215 chips; according to USB-C powered port.

 

[acowan]

yes of course ... stupid error thinking that would be accurate. So it looks like a short to ground on PP3v3_S5 and the USB-C controller might just be saving me from a fried CPU. Pulled R7691 and L7690 to isolate the voltage regulator. Despite U7650 looking like its had a blow torch on it the short is down circuit somewhere. Let the hunt being

 

[acowan]

Quick update on this

The short to ground on PP3V3_S5 on this board has ended up being a hard short (0.2ohm) at the CPU. Louis posted back in 2018 that almost all P3V3_S5 shorts on the new platforms have been CPU shorts. I swear it wasn't there when i started on this .. ahh well one for the parts bin