Hello,
Have an Xbox One S here that has a short on the 12V power rail. There is no power, beep, or partial fan spin when connecting power cable.
After diagnosing with thermal camera, Q9F1 MOSFET (NTTFS4C50N) is getting very hot. When I remove this MOSFET, the short on the 12V rail disappears.
I first replaced Q9F1 with one from a donor board and then partially reassembled the Xbox to test. When I plugged the power cord in, I got a partial fan spin and I thought I had fixed it, but unfortunately, the Xbox still did not power on. So I then disassembled the Xbox again and found that my newly replaced Q9F1 had blown again. So this time, I used another donor board and replaced Q9F1, Q9F2, and U9F1 which both of the MOSFETs are connected to. I checked to make sure the short on the 12V rail was gone and it was until I connected the Xbox back to power and it blew Q9F1 again.
What keeps blowing Q9F1? Looks like Pin 5 of Q9F1 is connected to L9F2 which is V_VREG_12P0_MEM_NBCORE and the other side of that inductor is the 12V line coming from the power supply (according to my interpretation of page 50 of the schematic).
I thought that maybe the power supply could be blowing Q9F1, so to test my own theory, I used a brand new power supply in case something was weird with the original and even using a new power supply, Q9F1 blew as soon as I connected it to power, so it’s not the power supply causing it.
Not sure what to check next. Hoping someone could help. Thank you.