SLI problem for cards in Slot 1 & 3

mac_angel

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Mar 12, 2008
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System:
Core i7 5930K x 2, Core i7 6850K
MSI X99S SLI Plus x 2, MSI X99A SLI Plus
MSI GTX 970 x 2, MSI 750ti low profile
4 x 8GB DDR4 RAM
m.2 Samsung 512GB SSD

So I'm having and odd, and frustrating problem since last fall. I built my system when the Core i7 5930K and X99 motherboards came out, and had 2 MSI 770 graphics cards for SLI. I ran them in Slot 1 and 3 so I could get better air flow and cooling. No problems. I later exchanged them for a pair of GTX 970s, and did the same thing, slot 1 and 3. I then bought a GTX 750ti low profile for a PhysX card for the middle slot so I could have as much air flow as possible. This all worked fine for a year. I wasn't playing any games that needed a PhysX card any more, so I took it out a while back to put in one of my other systems. I still kept the 970s in slot 1 and 3. Last fall I started having computer problems. I would shut down for no reason I could figure out (yes, I checked the event logs), so I RMA'd the motherboard and CPU. Got back a replacement motherboard and it had a big scratch on it. And I got a new Core i7 5930K, box unit. Plugged them all back in and no matter what I tried, the computer would not let the RAM run at the XMP profile settings, and it would not recognize a graphics card in the third slot. It did not matter which card I put in that third slot, the Board Explorer in the BIOS, as well as Windows would not see there was anything plugged in. I went through and RMA'd both the CPU and motherboard again, this time MSI promising they tested the board before hand and gave me the X99A instead of the X99S (only difference was the USB), and Intel gave me a Core i7 6850K (assholes kept trying to give me a Core i7 6800 instead). Got everything back, still have problems getting the RAM to work at the XMP profile (but I heard this is a common problem with the x99 mobos and CPUs - not the main problem I'm having), and again, the graphics card not being seen in the third slot. It runs in SLI if I put them in the first and second, though ends up throttling from heat, but no matter what card is put in the third slot, it's not seen at all, even if it's the only card plugged in. This was working for 2 years before hand without issue, now I can't get it to work at all.

Things I've tried.

- changing the cards around in different slots, different orders.
- changing the order of the power leads into the cards (all are 8 pin, but has the 2 that can fold away to make it a 6). Tried all available configuration orders for this.
- trying the m.2 in both SATA and PCIe configurations.
Trying the 4th slot instead of the third (still not recognized - shows the m.2 being plugged in there in the board explorer in either SATA or PCIe. I haven't tried unplugging the m.2 because it's the only drive in that system.
- tried the last three BIOS's
- when I started having problems with the computer last fall, I also tried changing the power supply before I did the first RMA for the motherboard and CPU. I haven't tried changing the power supply since, since it is working otherwise.

The system does work in SLI if I plug the cards in slot 1 and 2, just ends up throttling the speed, as I mentioned. Another odd thing is that if I have the two 970s in first and second slot, and put the 750ti in the third slot, it recognizes a card then, but the PCIe multipliers are weird. 8x, 16x, 8x. EDIT: After writing this, I actually remembered that was true before, and kinda stumped me as to why, but I didn't care since it was all working anyway. When I had the 970s and the 750ti in the middle, GPU-Z said the 970s were running in 8x and the 750ti was 16x.

I'm about to take the graphics cards apart to clean them up and reapply the thermal compound and stuff, hoping to get it to run a little bit cooler and hopefully not throttle as much since it seems, so far, my only option for SLI is back to slot 1 & 2.
Does anyone have any ideas what I might be missing?
 

mac_angel

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so, oddest thing. I took apart the two 970s, cleaned them out, applied new thermal paste, etc. Put them together, put them in the computer, with the 750ti in the middle again, and it all worked. Not a clue what might be different, but it's all working again, like it was before.
The only thing that I can think of is the order of the power cables feeding the graphics cards. Maybe I didn't try all possible combinations? which is now making me wonder if there might be an issue with the power supply?
 

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