He said he changed the riser the 2nd time he tried it. What are the chances that 2 risers sequentially were both internally shorted.
Really hard to diagnose without actually being there and seeing what the issue can be.
I know back in the litecoin days people destroyed motherboards due to uncut ribbon risers however with USB risers that's not an issue these days.
Thank you for the comment. Yeah, I understand, it's quite difficult, but at the same time I was almost out of ideas and things to try and 3 mobos, although I can RMA them, it's not a "cheap" thing to try.. I wonder if there is an easier way to test those without risking any gear.. Plug them in and start the PSU with the paper clip method to see what kind of power goes to the riser(s)?
Another thing is this: Currently, the system draws 1080 to 1100 Watts.. with the 7th card, this would have been over the 1200 Watts the PSU supports. However, in that case, it would have just shut down, not fry stuff. Is that assumption wrong? I don't think so, but I'm asking just in case, plus the PSU has short and OCP protection, although the short protection does kick-in in specific conditions so I don't know if a shorted riser will do the trick and trip the protection.