How do I stop large M/hash fluctuations in GUIminer?

[bartonn]

I have recently setup a new mining rig.  here are the specs below:
msi 750i motherboard
core 2 duo e6600
4gb ddr2
xfx 5830 (235M/hash)
sapphire 5850(275M/hash)
asus directcu 5850(275M/hash)
windows xp OS
750w psu
I have been mining on the computer for close to a week now, and always get the same M/hash with minimal fluctuations.  I have msi afterburner installed, and I would always have 100%gpu usage on all of my cards.  Today, I tried to overclock my asus 5850.  I increased the clock to 775mhz, but the m/hash on my other cards started to fluctuate, so i reset it to stock.  However, my 5830 and sapphire 5850 now has large m/hash fluctuations.  The 5850 varies from 180-240 M/hash and the sapphire 5850 varies from 200-275 M/hash,  but the asus 5850 is unaffected.  also, whenever I enter msi afterburner, my asus 5850 is always at 100% usage, but the 5830 and sapphire 5850 usage fluctuates between 80-97% usage. 
What could be causing the problem?

[zimpixa]

Maybe little low PSU? Its rather recommended to have ~700W PSU for 2x 5850 and u have additional 5830.

Also if you want to get it to normal stage reset your PC. Should solve it.

[bartonn]

I ran a test on my pc.  The 5830 and the sapphire 5850 ran stable without the asus 5850.  however, when i started the asus 5850 the M/hash began to fluctuate.  So it seems my psu can't handle all my cards.  however, I was able to run it for a week and my psu handled it fine.  When i overclocked the asus 5850, could there be any settings left over that allowed it to draw more power?
thanks

[Kluge]

Maybe little low PSU? Its rather recommended to have ~700W PSU for 2x 5850 and u have additional 5830.

Also if you want to get it to normal stage reset your PC. Should solve it.

This is possible. Each 5850 consumes roughly 200-225 watts at full load when overclocked. The 5830 consumes slightly less. That comes out to ~600-650w power consumption on the cards alone. After including the CPU, MoBo, RAM, & whatever peripherals you may have, you'll probably want at least a 850w PSU.

[dikidera]

Erm sorry, but the 5850 consumes 151 watts at full load at stock speeds.
The 5830 should be a bit less

[Kluge]

Erm sorry, but the 5850 consumes 151 watts at full load at stock speeds.
The 5830 should be a bit less

I should've noted "when overclocked 200MHz+"

My PC's pulling 480w from the wall with an underclocked & down-volted 3-core AMD CPU running @ 66%, with no peripherals, one SSD, and just one stick of RAM, which I take to mean almost the entire power draw is coming from the two 5850s I have in there.

Still, OCing that little bit may have pushed his PSU over the edge.

Some power supplies have very significant output degradation with heat increase. Simply cooling the PSU better may correct the problem the OP is having. It's a very common problem in laptops, and not impossible in desktops. The intake fan/vent gets clogged up, heat builds up, and output deteriorates. Many owners of gaming laptops find their laptop starts giving BSoDs after a year or few of ownership when it worked perfectly fine originally, and it turns out just giving it a good cleaning fixes it. If it is that problem, it could also be from the days getting hotter depending on where he lives.

[Kluge]

Try fiddling with (or removing) the -f flag, too. Try out -f 150

[bcpokey]

How are your cards configured? Might be thermal throttling as well, if you've stuffed all the cards close together.

Unless he has a signficantly inferior PSU this is unlikely to be the problem. Running 2 5870s OC'd 100Mhz and a 5850 OC'd 100Mhz with downclocked VRAM (make sure to do that OP) and a CPU @ 100% load, a few fans and an HDD my rig pulls 550W from the wall, which is probably closer to 475W from the PSU.
This is a significantly higher power draw systsem than 2x5850s and a 5830, which would definitely not draw anywhere near 600Watts.

[bartonn]

thanks for the help.  I believe my pc may be too hot, and either the GPUs or my power supply cannot handle the heat, since my room is probably over 80 degrees F.  soon, I plan to better cool the computer. 
thanks again

[d3athrow]

xfx 5830 (235M/hash)

<offtopic>you only get 235mh/s with your 5830, i get 260 with mine at stock and 290 at 1000mhz core</offtopic>