HELP!: GPU (HD 7950) Down-Clocking?!

[GeekMan]

Hello All,

I have a strange issue. ...

I run 4x 7950's on an Asrock Z77 Extreme 3, Intel Celeron, 850w PSU.
I have two machines that are identical, one works perfectly but the other has this strange issue.

The issue is this:  I can start mining (LTC) and after a short time, one of the cards down-clocks to 300mhz while the others stay at the clock speed I set in afterburner.

Here is where it gets stranger ... with 4 cards running, One will down-clock (Three running).  With three cards running, ... one will down-clock(two running).

What am I missing to ensure my card does not want to down-clock? 

Thanks

[sdhayes12345]

4 7950s on an 850W sounds like your issue. 

[GeekMan]

Note what I said above.  1.  One rig with the same setup does just fine.  2.  Even when I just run three cards, it down-clocks one of them. 

[MooC Tals]

Hello All,

I have a strange issue. ...

I run 4x 7950's on an Asrock Z77 Extreme 3, Intel Celeron, 850w PSU.
I have two machines that are identical, one works perfectly but the other has this strange issue.

The issue is this:  I can start mining (LTC) and after a short time, one of the cards down-clocks to 300mhz while the others stay at the clock speed I set in afterburner.

Here is where it gets stranger ... with 4 cards running, One will down-clock (Three running).  With three cards running, ... one will down-clock(two running).

What am I missing to ensure my card does not want to down-clock? 

Thanks

What miner are you using?

[middlemarkal]

a 7950 pulls at least 250W mining so 3 is limit on a 850W PS

[live627]

Try a powered riser...

[GeekMan]

It just does not make sense to me how one rig which is identical to the other down to the hardware, will run without issue while the other does have issues.

[MooC Tals]

It just does not make sense to me how one rig which is identical to the other down to the hardware, will run without issue while the other does have issues.

Are they all pointing to the same pool?

[jjiimm_64]

did you buy all 8? cards at the same time?  not all gpu chips are alike.

The 7970s i bot last year are able to clock lower then the ones you can buy now....  every chip is different.

try switching the cards from one rig to the other rig to check this.

[MooC Tals]

lol I had the same problem and that is why I was asking my questions. However now I will unwatch this thread and ignore your problem. Good luck

Ciao

[mufa23]

According to Wikipedia, the 7950 pulls 180w http://en.wikipedia.org/wiki/Radeon_HD_7000_Series#Southern_Islands_.28HD_7xxx.29_series

Running four of them is pulling 720w just for powering the videocards. Now assuming the 850w PSU is 85% efficient, you have a total of 722.5w that's useable for the entire rig. With the motherboard, RAM, and CPU (and HDD?) you are probably pulling another 50w+ to power those. Which means, you probably need 770w+ to properly power everything. Which is probably more power than your PSU can handle. And there is more things to factor in such as how many rails your PSU has, and what the maximum wattage/amp is per 12v rail.

If your PSU isn't causing your particular issue, it's still a major concern that you should look into. I'd highly suggest either upgrading to a larger PSU on both rigs, or taking a card out. You are stressing those PSUs.

(assuming of course, that my understanding of power use in computers is correct)

[Beremat]

I believe efficiency is measured the other way around, meaning the PSU can output 850w but will draw 1000w from the wall. Otherwise you're pretty spot on!

The most important thing for GPUs, like you said, is to look out for is the PSU's capabilities on the 12V rail(s). If OP's PSU can't output 720w on the 12V rails then it doesn't matter what output it's rated for. Either way I think he's cutting it pretty close. 720w for the GPUs leaves 130w for the rest of the system. PSUs age, too, so their output decreases over time. That might be the issue.