Surface pro 5 (Model 1726) missing 3.3V power rail

[noflux]

Hello All

Have a Surface pro 5. Main board model; M1007506-015. Main 15v power rail is present.

1st image;
Missing 8v rail at inductor (circled in blue). Suspect main cause is power is being drawn at dead short on C4517.

2nd image;
3.3v rail was measured at 0.17v (at top most capacitor with red cross in 1st image).

Capactors crossed out in red are shorted.

Are the 5v and 3.3V rails tied in somehow e.g. generated at a single IC?

2nd and 3rd image;
C4517 circled in red is shorted at pin 1 (+5v USB power) and get very hot need some information on what component is and value.

[Sephir0th]

Re: Surface pro 5 (Model 1726) missing 3.3V power rail

Remove it to start with and look whether the short to GND disappears. From there it might be possible to find out the specs of the Cap if you share a clear picture of the top marking.

[noflux]

Re: Surface pro 5 (Model 1726) missing 3.3V power rail

Removed capacitor circled in red, Cap is fine, pinpointed short due to something conducting between the USB port and its shield. Short has now gone. although tested without cap connected getting just under 3.3v. With no cap the 6 pin IC next to it get hot, but stays cool when new cap is soldered on, the cap then gets hot. IC tested and pins are board are fine. it seems this IC is on the 3.3v rail. (will replace once I can identify).

2 small MLCC Caps crossed out in picture are a different matter. after some checks and some more components removed the short is on the +3P3VA line. as this line seems to be all over the board and there are multiple components its a bit difficult to pinpoint, nothing seems to be getting hot also, and sadly dont have the tools for voltage injection.

Does anyone have any schematics for the 5v and 3.3v rails. or know where these voltages are generated.