(SOLVED) VERY low hash rate on ONE card (2x 7950)

[ollebolls]

Hello,

My first post here, I have just started to do some mining using two XFX 7950 cards.
I have a 850W PSU and MSI motherboard and I have a very strange issue. I was hoping any of you fine people could help me out!

One of the cards is getting around 500-600 khs but the other one is only getting around 80.
I use the following setup

cgminer 3.7.2
ATI drivers 13.10
SDK 2.8

This is how I start cgminer (start.bat)
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer --scrypt -I 16 --thread-concurrency 21712 -o stratum+tcp:// -u xxxx -p xxxx

I have tried all kinds of different settings, setting vdc and gpu clock etc.. I also tried using the cgminer.conf with same settings on both cards, still same result.

What am I doing wrong? Why is one of the cards not doing its job?

Thank you!

/O

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[tekkx2k13]

Hi,

my guess, you need to setup cgminer for 2 cards

cgminer --scrypt -I 16,16 --thread-concurrency 21712,21712 ...

there should be some howtos on the net.

kind regards

tekkx2k13

[ollebolls]

Hi,

my guess, you need to setup cgminer for 2 cards

cgminer --scrypt -I 16,16 --thread-concurrency 21712,21712 ...

there should be some howtos on the net.

kind regards

tekkx2k13

Hello,

It does not help. If I place the settings in a cgminer.conf file for both cards, with the same settings the card number two will just do nothing.
Screenshot:

http://imgur.com/U8iasWB

/O

[delovan]

Hey, I got the same thing when a set up my rig.

I tried to make a rig with 3 7950 with a 760 watts 80+gold psu. The 3rd card was like your one, only 80kh. I switched many times, but the thrid pci-e slot refuses to make more khs.
And when I used only two card, even on the 3rd pci-e slot, everything was right.

So it ends up to the conclusion : my psu wasn't enough to supply 3 card, even with a gold psu. I would say that your psu is kinda broken, since 850 w is clearly enough to run 2 cards. Is that a 80+ psu ? Remember that 80+ means 80% of power delivered, so 850*80% = 680 watts

[ollebolls]

Hey, I got the same thing when a set up my rig.

I tried to make a rig with 3 7950 with a 760 watts 80+gold psu. The 3rd card was like your one, only 80kh. I switched many times, but the thrid pci-e slot refuses to make more khs.
And when I used only two card, even on the 3rd pci-e slot, everything was right.

So it ends up to the conclusion : my psu wasn't enough to supply 3 card, even with a gold psu. I would say that your psu is kinda broken, since 850 w is clearly enough to run 2 cards. Is that a 80+ psu ? Remember that 80+ means 80% of power delivered, so 850*80% = 680 watts

Hi,

This is the PSU I'm using:

XFX ProSeries Black Edition 850W PSU
ATX 12V V2.31, 80 Plus Gold, Modular, 6x 6+2pin PCIe, 10x SATA, 5x Molex, 1x FDD

So I guess that could be the case

[delovan]

Well, 80+ gold is 89% so unless your psu is a little broken, you must seek another reason. Maybe test another PSU.

[chunkylover53]

are you undervolting your cards at all ?

I had mine undervolted and one card was stable but the other wasn't. Had to find a value that worked for both.
I use two cards which have 2GPUs so I have 4GPUs but i only specify thread concurrency once ie --thread-concurrency 8192 not 8192,8192

[pocketOcoins]

Yes you have to under-volt the cards and flash the bios to make that happen..good luck!

Research your card and you should be able to find some online directions and the file you need. 

[ollebolls]

are you undervolting your cards at all ?

I had mine undervolted and one card was stable but the other wasn't. Had to find a value that worked for both.
I use two cards which have 2GPUs so I have 4GPUs but i only specify thread concurrency once ie --thread-concurrency 8192 not 8192,8192

Hello!

No not undervolting at all. I did a test though.
I disabled one of the cards in the device manager and just ran it by itself, it produced the expected khs. Then I disabled that card and enabled the other card and tested that one, same result. So both cards work. I think you are all right that this is related to the PSU.

I only have a 650W bronze cpu at home, do you think it is worth the try?

I also thought that maybe connecting more cables from the PSU as it is modular, so that each connection on the GPU gets a dedicated cable. Right now the connections are two cables from the PSU and then two connectors on the GPU's. But if I switch to four cables and one to each connector, perhaps that will make any difference. Thoughts?

Thank you all for your kind help!

[delovan]

650W bronze is clearly not enough. I run 2 card with a 720 bronze but, barely. I cannot add any further disk and I got a limited cpu.
What you should try to do is plug your 2nd psu to power only one of your card, and the other one powered by your main psu.
While this solution is not recommended for production purpose, you can test it anyway to make sure the problem is from your psu, and not related to the mainboard.

[ollebolls]

Hello all!

Thank you all for leading me in the right direction, the PSU.
I don't know how many hours I spent troubleshooting this, but now it seems to work!

I did the following

1. Added another cable from the PSU to one of the cards, so each cable has two PCIe connectors, I added one cable and used one of the connectors on one of the cards.

2. I changed power outlet for the computer, just put it in another outlet. I used the same connector in the wall where I usually connect a BBQ, so I know that has plenty of power

I now do around 600khs per card, which is fairly ok.
I will do some testing with underclocking etc now that it is working properly and no more 80khs.

THANK YOU ALL!

[dopevalla]

Hey, This is great.

Let us know your results.

I do have the same config and like to start mining next week.

Your brainstorming might help me, I think.

Good luck