[aSpartan111]

Hello all,

I'm posting on your forum, regarding an issue i'm having on one of my Origin 350 Brick.

As soon as i power it on, the red fault led turn on and the message "PCI 5V low fault reach @ 0.104 V" is displayed, then the brick turn itself off.
To diagnose it i removed every PCI cards including the IO9 board and the cpu node, but the fault is still present.
I also tried swapping the 2U Pci riser with the one from another brick (that has no issue), but the issue remains.

At the moment i'm trying to do component level board repair on what i would call the motherboard (2U Interface 030-1809-006).
And on it, i measured a capacitor (220µF 6V) with 38mV on its +Pin.
This cap is near an LTC1629CG (synchronous step-down switching regulator) and we can spot some components shown in the typical application (attached) from the datasheet.
The 4 Mosfets (D-pack), 2 Inductors, 2 3mOhms resistors, etc

I measured the obvious continuity/voltages.
- I have 12V at Vin (through a 10 Ohm res)
- The gate of each Mosfet is connected to its TG1/TG2/BG1/BG2 respectiv pin
- The 2 0.003Ohm Res are connected to their respectiv sense pin (through a 100Ohms Res)
- There is no obvious shorts on the mosfets, diodes nor ceramic caps
- I measure a brief 5V at startup, and quickly it falls down to near 0V
- There is a 300 Ohms resistance when measuring between the + and GND of the output Cap (the 220µF 6V one) which is about the same compared to the other LTC1629 circuit on that board ( 3.3V output IIRC)

What else could i miss ?
Could a zener diode be dead ?
A reset i'm not aware of ?
Or maybe a DS1780 not properly measuring and/or shorted ?

I would greatly appreciate your input/ideas if you are a seasoned component level repair expert as i am not necessarily one.
I'm pretty comfortable with electronics and desoldering, i also had great success repairing numerous switching PSUs (easy when there is an obvious short... ), but on this one i'm a bit dry.

So far i managed to gather informations on the internet (including your forum) every-time i had an issue, but this time i think i might need help.
I'll keep looking for answer on my side (reading datasheets, measuring, etc) and post it if i find anything valuable.

Thank you all for reading, and maybe your future posts.