I am trying to attach a third GPU to my personal computer to mine on the side. My computer is already using an AMD (RX580 Gaming X 8G) to dual mine ETH+SC using Claymore and I have an Nvidia GTX 980ti to mine SC using Marlin. These were both running perfectly for the past couple of days, and I got my hands on another RX580. Since the initial two cards are already in full 16x slots I can't fit another in due to the fact that there is no more room in my case, so I thought I would just add it by using a riser. However, I can only get 4 MH/s hashrate out of the 580 in the riser, and when I test it by itself (full 16x) slot I can get 29 MH/s. I already tested two risers individually and with other cards so I know that the risers work. I have also tried changing to PCIE slot that the riser is in to both GEN2 and GEN1, but that didn't change anything.
I am just wondering is it possible to have 2 cards in full slots and attach a third using the riser. My computer picks up the third card, it just does not mine well and takes a long time to create the DAG.
I am running windows 10, 750W PSU (again this is my personal computer), and my mobo is a Asrock Z170 OC Forumla.
Is anyone doing something similar?