Hello good people. I have a problem and I'm not sure where to put the blame. I'll give a brief description of the problem after I tell you my specs. My system is homebuilt almost 2 years ago. It is as follows:
Case-- Coolermaster Centurion 5
PSU-- Antec NEOhe 500W (modular cabling) More on that in a moment
Cpu-- Opteron 170 w/Thermaltake "Big Typhoon" cooler
MB-- Asus A8N-SLI Deluxe
Ram-- 1 gig Corsair Twinx XMS dual channel kit (2 x 512) 2-3-3-6 1T timings
Video- Asus Geforce 7600gs 512megs (passive cooling)
Floppy/cardreader-- dvd/rw drive-- 2 Seagate 160 Sata hard drives


My system started having power issues some time ago. The first psu I put in when I built it was an Antec TruPower 500W which started having issues and had to be RMA'd back to Antec. They were very good about it and replaced the defective one with a NEOhe 500W (seems the Trupower 500 was discontinued). Things went ok for a while untill I started having issues starting the computer up. If it was shut down I had to press the start button up to five or six times before it would finally start, (all the while the fans and light would be coming on and then going off. Sometimes if I tried too many times to start up it would reset the cmos and I would have to go back into bios and set up all over again.

Again I called Antec about it and went over the symptoms, switching the power and reset switches on the motherboard but made no difference. Again they were very good about replacing it. Now I am on my third Antec psu, and it did indeed solve the startup problems. Now, however, after only a week or so since installation, my computer has developed some new power related problems. I have had this system overclocked to 2.8ghz stable for quite some time, and last night after doing some tweaking I ran prime95 for about 8 hours. (No errors!) I stopped the test this morning and figured all was well. Then I tried to run Super_pi multiple times and could not get a correct checksum. I tried several small changes in voltage (vdimm, vcore and ram timings) none made any difference in super_pi, (still incorrect checksum). I even set the bios back to default settings and still could not get a correct checksum. I ran memtest 86 for several complete runs and had no errors.

Now this evening, I noticed (using speedfan) that my temps were randomly spiking and then going back to normal. I wasn't even running any programs at the time. I checked using cpuz and found my vcore was fluctuating from a low of 1.39v all the way up to 1.5 on occasion. I don't want to think about another RMA, but I will if I must. Does anyone know if this could be a bios issue or some hardware issue on the board. I keep all my mb drivers up to date and bios is latest version, but it seems unlikely that 3 PSUs from the same manufacturer would all turn out to be lemons. I f anyone has any Ideas, I would be most grateful for the input. Thanks in advance.

I would suspect the motherboard; you've already tried 3 power supplies. You can try an rma with asus. My own experience with rma's is that they send you a different board that's been checked, but not new. Socket 939 boards are in short supply. You may get lucky and get the same replacement board from asus. I found a vender recently selling your board for over $200; but it's been awhile since I last checked. Another option is to try your board at the default settings (no overclocking) and see if the voltage is more stable.

I would agree with Oldie. I have been running the ASUS A8N-SLI Deluxe for years. Currently using an FX-55. I ran it at 2.9-3.0MHz for a long while and the PSU gave out finally. I think all the overclocking had something to do with that. Burned up a Crucial Ballistic PC4000 DIMM too with all the voltage increases needed for the overclock. I installed a new middle-of-the-road quality 500 watt Coolermaster and a couple of new RMA DIMMS and the system runs fine with two 7600GT's, 2 hard drives and 2 optical drives, but I backed down the overclock and use it in one of the offices now. I have none of the issues you are having. The PSU's you are using should power your system easily. 7600GT's get their 12v power from the PCIE slot (maybe that's what going south on your MB). Looks like you have gone over your system petty well. You also sound like you overclocked the holy crap out it! You have tweaked and troubleshot about as well as anyone could. I would agree with Oldie, sounds like some other problem than PSU. I think weakened voltage regulators on the MB are a good canditate? Here some info.

http://www.pcstats.com/articleview.cfm?articleID=195

Would mention too these old socket 939 NF4 ASUS MB run extremely hot at the NB. I also have the A8N32-SLI up and running with 4800X2. That particulary Mb is one of the hottest running MB's ever released! I have fans velcrowed to the bottom of the case blowing upward to video cards.

Thanks very much for the input. I just re flashed the bios with a freshly downloaded copy of the same version. I don't think it solved the problem, however I think that it might have reduced the spiking a little bit. I am in Ubuntu right now, (I dual boot between Linux and Windows XP). I am going to reboot into XP and run a few more checks with cpuz, maybe in the faint hope that the bios had something to do with it. More on this later. I appreciate the help immensely. By the way I have never set the Vcore over 1.45, thats why the spikes had me so concerned. Also, would the voltage fluctuation cause it to fail super_pi and still run prim95 for 8 hours?