Thoughts on value for replacement SMT 0603 fuse on PCIe gen 3 card?


It turns out the Supermicro AOC-2308 SAS controller cards are not hot-swappable - who knew? (I should not be doing firmware updates when tired.)

Got a spark flash when plugging it in.

Anyway the card is dead, but the most obvious problem is an open circuit 0603 (freedom unit (nested joke about imperial units used in the USA)) SMT fuse marked F1 on the board. It is bright white and has no markings. I had other cards to do an A-B test on. Probing beyond the fuse seems to show its OK.

Anyone know what the fuse product line might be or a value suggestion? I can’t find any schematics for the card but it is likely to be a reference LSI design that supermicro copied.

I would rather not bridge the fuse and risk the whole server if I can avoid it…

Followup from me:
So, as I ended up in a hurry I bridged it, checked for no shorts on the power supply and shoved it in a burner PC to test. Worked fine and currently undergoing stress testing in actual server.

From another forum I got a note that 0603 fuses max out at 6A so I should use that value to have “some” kind of fuse to protect the server.

Great controller cards though, I got an extra 500mb/s out of the iSCSI volume using them over 40gbe. I wonder if it is the extra MSI-X irq’s for the SAS2308 vs. the older SAS2008 SoC’s, as the card bandwidths seem more than enough for spinning rust drives.

From what I can read on the interweb, PCIe max power delivery is 75W from the PCIe connector on the motherboard.
Assuming the fuse directly protects the 12V supply, it shouldn’t be more than 75/12=6.25A.
Now, 75W would require active cooling and quite a big heatsink. As your SAS controller just seems to have a small heatsink and no fan (at least on google images), it’s probably nowhere close to 75W.

I would probably put a fuse in the range of 3-4A to provide some protection, and still have something to protect the rests of the system just in case :slight_smile:

Measure the parameters you can like DC resistance and inductance of one from the good cards, then use that together with your best guess of the max current to choose one from the most common similar looking range of 0603 fuses, maybe Bourns or similar.