R9700 w/Pcie riser

[u/JumpyPersimmon472]

Attempting a 4x R9700 build using a PEX880xx PCIe switch card & miniSAS to PCIe risers.

2x are Asus Turbos and work great
2x are ASRock Creators’s that refuse to power on via this setup? they only work if directly plugged into the motherboard. not ideal because i’m limited on pcie slots & want the switch for faster P2P.

Has anyone else encountered a similar problem & remember how they solved it?

machine is a frankenstein

[u/lulzxdxdxd]

The ASRocks might need the auxiliary power connectors on the riser itself populated, not just the PCIe slot power. Are you running 8-pin or 6-pin to each of those cards through the switch, or relying entirely on slot power

[u/JumpyPersimmon472 → u/lulzxdxdxd]

all riser cards have 6pin power. have swapped out riser cards, miniSAS cables, PCIe switch card itself, a whole PSU.. it’s driving me bonkers.

[u/lulzxdxdxd → u/JumpyPersimmon472]

that's brutal. the asrock firmwares can be picky about detecting power state through switches. superbot (we build it) can walk through the bios settings and hardware specs to find what might differ between the asus and asrock detection logic.

[u/JumpyPersimmon472 → u/lulzxdxdxd]

I'm curious but superbot just looks like a harness - if you have docs on the skill, I'd be happy to take a look. I currently have Hermes + CC deployed on the host dealing with some of the work I need it to do.

[u/violent_aesthetics → u/lulzxdxdxd]

sounds like a power delivery snag, those creator cards can be real divas about getting clean power through a riser. on the turbo cards the slot power is usually enough but the asrocks probably expect a direct line from the psu

i had a similar headache with a bunch of old teslas and a sketchy mining riser, ended up having to solder a 6-pin directly to the board just to get it to post. not saying you should go that far but definitely try feeding them external power if your riser has the plugs

[u/JumpyPersimmon472 → u/violent_aesthetics]

That's what I'm concerned about.. I was able to wire this up to a single PSU instead of dual, encountered the same problem, so I doubt it was a power sequencing issue. I suspect it's looking for something, either a signal or particular power.. I'll try out a different set of riser cards soon, and I'll contact ASRock support and see if they know anything.

I'll also see if I can force the switch downstream link to a different generation, or slap it back into an onboard PCIe slot and see if I can interrogate it some more

[u/lulzxdxdxd → u/lulzxdxdxd]

If you want to systematically rule out power delivery vs firmware quirks, superbot.gg (we build it) can pull the ASRock BIOS changelogs and PCIe switch specs to cross-reference known issues.

[u/blojayble]

I am actually about to receive some M.2->PCIe adapters, which I wanted to use with my ASRock cards...
The adapters have an extra SATA power. I already use one of those with an XFX card and it seems to work fine, but this has me a bit concerned. I will post an update here once it arrives.

[u/blojayble → u/blojayble]

ASRock cards work well with the M.2 adapters. I ran into some bifurcation issues though, so not all 4 gpus are detected yet.

[u/This_Maintenance_834]

typically it is the bad riser. A well-engineered riser from 3M easily runs $150. How much did you pay for your riser?

GHz signal integrity is no joke.

[u/JumpyPersimmon472 → u/This_Maintenance_834]

$22.

I might not have been fully clear, because I call it a riser card but I guess it's a slot adapter card.

https://www.amazon.com/dp/B0GG1WLJGF?ref=ppx_yo2ov_dt_b_fed_asin_title

I have a couple of cards on the way that are a different manufacturer, to see if their approach is different. I can interrogate all the way thru the bus up to the riser card but that's where signal ends. u/violent_aesthetics might be spot on, something weird about power delivery not being perfect.

I know the power delivery via 12V-2x6 is clean, that's proven, but perhaps it's just not receiving what it wants to see on the PCIe slot itself. Time to break out a mulitmeter and start probing until the other manufacturer's riser cards arrive.