Topic: Can't get gpu-threads 2 working on multiple r280x GPUs *SOLVED* (Read 1273 times)

Glad you could figure it out! I HATE multi-rail PSUs for mining. Yes, you can load balance your GPUs across multiple rails, but I always feel it's a waste. I prefer a single, strong 12V rail, and you can't go wrong!

one word:  RAILS

This is a new one for me.  Either I got lucky last time I built my SLI windows machine, or the cards weren't power hungry enough compared to my PSU... but in this case, it's all about the RAILS!

When I originally connected up my wires I figured given the modular design of the connectors, there was no way to wire it wrong.  Two GPUs per PSU, red goes to red.  Being a little OCD, I liked the look of VGA1 and VGA2 being populated in each PSU... FAIL!

Moral of the story... put one GPU per rail... in my case it was VGA1 & VGA3 (or VGA2 & VGA4) on the PSU.

Ugh!  No matter... I'm just glad it's solved.  Hopefully my public humiliation will help future miners avoid the same pitfall.

More reading on Rails:
http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-Power-Supplies/181/12

Your PSU do not have enough power.

cgminer:
"intensity" : "13",
"worksize" : "256",
"kernel" : "scrypt",
"lookup-gap" : "2",
"thread-concurrency" : "8191",
"shaders" : "2048",
"scrypt" : true,
"failover-only" : true,
"gpu-reorder" : true,
"gpu-engine" : "1040,1040,1040,1040",
"gpu-fan" : "80",
"gpu-memclock" : "1500",

Box : Cooler Master HAF X
Motherboard : Asus Maximus V Extreme
Processor : Intel Core i7-3770 Quad Core 3.4 Ghz
CPU Cooler : Cooler Master Hyper 612 PWM
Memory : 4 x 4Gb Kingston HyperX Blu Black Series DDR3-1600 CL9
2x Power supply : #1: Thermaltake Smart M1200W Series(Motherboard + CPU COOLER + 3xFAN + Hard Drive + 1xGigabyte R9 280X)
#2: Corsair Professional Series Gold CMPU-1200 1200W(Outside the box - 1x Gigabyte + 2x Sapphire)

2x Gigabyte Radeon R9 280X 3GB GDDR5 (Windforce x3) OC GURU II
2x Sapphire Radeon R9 280X 3GB GDDR5 Vapor-X

Stable around 730kh/s at 65°c outside of the box.

Crazy!! As much as I don't want it to be a PSU thing... it might actually be?!  I need to investigate more, but here is what I discovered (thanks to your prompting).  If I put one GPU on each PSU, both will run at gpu-threads 2.

Here are the Watts:

PSU#1 (numbers include LCD)
54w idle with MB, CPU, 2 GPUS on motherboard, but powered via 2nd PSU)
105w while mining at gpu-threads 1 (both GPUs powered by 2nd PSU)
326w while mining at gpu-threads 2 (one GPU on each PSU)

PSU#2
246w while mining at gpu-threads 2 (one GPU)

For the life of me I can't fathom how these brand new 750w Gold PSUs can't handle 2 GPUs who's combine load is under 500w?!
http://www.evga.com/Products/Product.aspx?pn=120-PG-0750-GR

Next I'll start playing with cords and VGA PSU slots to see if there are some magic combinations.

I'm using any flavor of litecoin_BAMT (currently Litecoin BAMT 1.3  with Catalyst 13.11)
more info here on the various versions: http://bamt.wikia.com/wiki/Litecoin_BAMT#Versions

Mining on wafflepool

here are my current settings in the cgminer.conf and stats

post your config or command line.

So you can run one card at a time, but not both at once? Sounds like a PSU issue.

I'm building a new mining rig but can't seem to get past this problem.  Each GPU can run with gpu-threads 2, but if both are set it will only mine for a few seconds before the video signal fails and the GPU fans spin down to idle... the system then requires a reboot.  I've tried various Catalyst drivers, litecoin_bamt installs, powered risers, GPUs mounted directly on the MB, even flashed their BIOS to run a lower voltages.  Together, they pull under 500w before it crashes... no visible power spikes or other oddities.  I'm running out of ideas, so I'm willing to try just about anything.  In fact, even if I've tried your suggestion in the past, I will try it again and post hard data where applicable to best document this problem (and solution hopefully).

Here are some specifics on my hardware:

I used this guide: http://www.coinminingrigs.com/how-to-build-a-6-gpu-mining-rig/
MB: MSI Z77A-GD65
CPU: Celeron G1620
RAM: Kingston Hyper X Blu 4 GB
PSUs: 2 x EVGA SuperNOVA NEX750G
GPUs: 4 x GIGABYTE GV-R928XOC-3GD rev2 r280x
I've posted about this problem in another related thread, but the replies get lost and so does the momentum for finding a fix.  I'm hoping I will be able to update this thread with the large bold SOLVED before the weekend is over

Related thread I posted in... (Most of the suggestions centered around power issues):
Original post: https://litecointalk.org/index.php?topic=2924.msg110819#msg110819
Recent post: https://litecointalk.org/index.php?topic=2924.msg134596#msg134596

I have also posted this on the litecointalk.org forum and will update both if a solution is found:
litecointalk post: https://litecointalk.org/index.php?topic=16519.0