Bitcoin Forum

Hello,

I have 5 Sapphire 3L 7950s on one motherboard with powered rises on all of them. 3 of them are 16x to 16x and two are 1x to 16x...i started having really bad stability issues out of the blue tonight on settings i had been using for the last week without issues. Drivers started crashing constantly (im on windows), so i re-installed the proper drivers and was still having issues. So i went to disconnect one of the cards and realized the 12 volt cable in my molex power adapter on the riser had come loose. I re-attached it and my rig is now somewhat stable, but still not what it was. (i was running vddc 1075, gpu code 1025 gpu mem 1575 all week)

Anyway I notice when i go into Trixx (overclocking software) the voltage on the 3 pcie 16x to 16x cards have a default vddc of 1.250v  (i am currently undervolting to 1.075v with gpu core at 1000 and mem 1400) but the weird thing is the two 1x to 16x default to a vddc between 1.116v or 1.160v. Is this because the powered risers aren't working properly? Here is the link to the risers I bought, and insight would be much appreciated.

http://www.amazon.com/PCIe-1x-Extender-Bitcoin-Mining/dp/B00D35G02G/ref=sr_1_23?ie=UTF8&qid=1371981236&sr=8-23&keywords=pcie+1x+to+16x

its not recommended, but my method is to touch the plastic connection of the 24pin connector. if riser not doing their work it will get pretty hot.

if its working ok it should have no heat at all

The technical way to do it would be to use a digital multimeter to check if there is an electrical connection between the molex pin and the PCI-E pin responsible for power supply.

If you really wanted to be sure you'd break that connection somewhere along the power cable and put the multimeter in to fill the gap and measure the current flowing down it.

I had the blue screen crash error.  Make sure you have set your pci x16 slots to Gen 1 in your bios settings, also make sure the risers are AS STRAIGHT as possible without kinks.  This seems to limit instability and crashes for me.  Undervolting also seems to help.

The main probelm I have with risers it making the motherboard recognize the cards when on risers.  So frustrating,  like 90 percent of the time the motherboard will not post with risers.....

Once its running though it can go for weeks.... strange.

what board do you have? also are your powered risers sharing the same molex lines (as in separate lines to PSU)? i had one rig that ran fine for days then i messed with it and it wouldnt boot. all cards boot fine but when combined no boot. put the risers on separate molex leads and it worked fine since. seasonic 1050w power supply. whats crazy is i have some system using ocz 850w psu's and have them doubled up on molexes with no problem at all.

also if your psu is not single rail it could be pulling too much power from one rail. i would suggest a psu issue if its not posting. also i bought some risers cheaply made and the yellow would push partially or fully out when you plugged it in so i just plugged that lead directly into the psu molex for a tight fit

Turns out one of my big issues was shitty drivers. This has improved my stability. I have two cards per rail with my 1600w LEPA and 1 card on the same rail as my HDD. Seems to be working pretty good now. I had the same issue with the cheaply made ones and the yellow cable popping out, if it happens again I'll do what you did and plug it directly into the psu molex.

Thanks!

Feel the chord. If its incredibly hot its not working.

incredibly hot =  wire too thin, but working.