Just registered to come and say thanks for this thread. It helped me get 3x1080ti (1x16channel, 2xRisers) going on my H81 Pro, even though it was not plug and play.
As I was just happy to get them going, this is not a full "debug", but some things that seemed to help, or didnt at least harm the process
- AS Rock H81 Rev2.0 with 1.20 BIOS. I turned off everything I didnt need to be using, and maximised the compatibility/stability settings
- 4gb DDR3 RAM, Pentium G3260. Increased the pagefile to 16gb, as NiceHash was getting out of memory errors even after first two card up and running.
- Window 10 Pro. Build 1609. I did the hackflag registry fix "just in case" but actually the second card was found when I removed the hackflag key again.
- NVIDIA drivers 388.43. I just kept doing a clean install of just the drivers once another card on another PCie channel was found.
- Getting a single card going in any of the channels was not a problem. I used this process to make sure I had two working risers to eliminate the "bad riser" risk, and then left the first card in the mobo slot.
- I finally got a second card working on one of the risers. Not really sure how I managed that, but lots of rebooting, bios flashing etc.
- But the the third card would not work and a third slot, until I took out the second card, got the third card working, then added the second card back in.
So in summary, if I had to start from zero I would try this to make it work with less trial and error, basically adding cards one at a time, but only adding card N to a slot that was already working with N-1 cards:
- Get one card/riser going in one slot. Install the drivers.
- Use the same working card/riser combo in a second slot to "activate" that slot. Install the drivers
- Hopefully get two cards running on the two "active" slots.
- Move one of the cards to a third slot to "activate" it. Install the drivers
- Add the third card, using all three "active" slots. Etc...
Hope this helps someone else, and for my 4th card once the damned riser arrives...
Danny