[solved] Gigabyte Intel NUC Failure

[gnif]

Hi All,

I was given a i7 nuc that appears to have had a PSU fault. The device powers on and the 1.8V, 3.3V and 5.0V rails are all stable, however it just let the magic smoke out of the CPU fan where it's dumping unregulated 19V into, so it seems the 12V regulation has failed. I am trying to trace it though but need to identify a 5 pin device that I think is a MOSFET, marked what looks like Q5RDT.

See attached.

This device is connected to the resistor just above PQ6 which is controlling PQ6's gate. At power on the gate is pulled low and 19V is produced on the other side. A continuity check shows a connection between the output of PQ6 and the CPU fan power pin. I would have thought that this signal should be switched as some kind of switching regulator producing the 12V, but I could be completely wrong. Any advice would be greatly appreciated.

Edit: Think I found it, missed a switching reg on the other side of the PCB... its been so hot the solder balls have come out from under it.

[gnif]

Just for completeness, there is a buck converter near the fan header on the opposite site that has died, a GS9238, seems it's internal gate has failed short dumping full rail onto it's output.

[Whales]

Feed the board with 12V instead of 19/20V

EDIT: I know that fans tend to be one of the few things that still use 12V on modern motherboards (other than the main bulk CPU/etc supplies, but they will probably be taking 19V direct on this board).  I wonder if USB 3/C chipsets now also take 12v, and might have been damaged?

[gnif]

Feed the board with 12V instead of 19/20V

Unfortunately not an option, the PMU wont allow it to start under 17V.

EDIT: I know that fans tend to be one of the few things that still use 12V on modern motherboards (other than the main bulk CPU/etc supplies, but they will probably be taking 19V direct on this board).  I wonder if USB 3/C chipsets now also take 12v, and might have been damaged?

Not sure, I removed the IC and the system now starts up and doesn't reset. I found the same part on ebay for $6 for 5, so ordered some, in the meantime I can just power the CPU fan externally and learn what this little beast can do

Edit: Yes I did measure the IC out of circuit and it is indeed shorted out
Edit2: USB3 ports working fine even without the 12V rail.