VCore varying - Is it the PSU?

[RAndersen]

I just put together a system with an AMD 2100+ tbred (AIUHB0301) w/ Volcano 7+, Asus A7N8X, 2 sticks of Corsair XMS PC3200 and a Gefore4 TI4200. I'm using the generic 350W PSU (brand is TVU) that came with a cheap Foxconn Super Case. I'm running right now at 175x12 with vcore=1.75 and everything seems stable. The problem is if I try to increase the FSB any more I start to get random reboots.

The problem seems to be a varying vcore. According to Asus Probe, the vcore while running Prime95 varies from 1.78 up to 1.84 at some points. It really seems to jump around a lot. The other voltages all seem pretty stable. I'm wondering if this could be caused by the cheap PSU or is it some other problem? I'd really like to get the processor to run a higher FSB, even if it means lowering the multiplier though I think this processor should overclock a little better.

Any advice as to why the vcore varies so much or what I can do to increase the fsb would be appreciated. I'm afraid to raise the vcore any higher in the bios since it would probably start going above 1.9v during usage. Right now the cpu idles at 40C and runs at 51C full load.

Thanks,
Rob A

 

[chizow]

You've pretty much answered your question

Cheap PSUs will fluctuate due to poor voltage regulation circuits as well as less than advertised power to the 3.3V and 5V lines. A good 350W PSU would be fine, but a cheapo one as you indicated often exhibit these symptoms. You may also want to try raising your Vdimm to 2.7V before you go out and buy a new PSU, as that is the recommended voltage from Corsair to obtain 200mhz FSB speeds. It seems like your Vcore isn't undervolting too much, but fluctuations will also cause instability.

Chiz

 

[RAndersen]

Thanks for the info. I pretty much figured it was the cheap PSU. Is the vcore controlled by the PSU or is it from the motherboard? I'm interested since the other voltages seem to be very stable and only the vcore varies up ad down.

 

[chizow]

Originally posted by: RAndersen
Thanks for the info. I pretty much figured it was the cheap PSU. Is the vcore controlled by the PSU or is it from the motherboard? I'm interested since the other voltages seem to be very stable and only the vcore varies up ad down.

The Vcore, or the actual voltage supplied to the core, is set by the mobo, but is only as consistent/accurate as the PSU supplying it power. There have been bad capacitors and such on mobos in the past, but fluctuations are typically the result of underpowered PSUs with poor voltage regulation circuits.

Its not uncommon for only the Vcore to fluctuate, as it may be the only line stressed in your system. Testing it under load is something most don't do, saying their voltages are "fine" (when idling in Windows hehe), so good job there Also, check to see how much the actual rated W's are to the 3.3V and 5V lines (they power the mobo and its components). Most cheapo PSUs advertise XXXW, but in actuality, underpower the important shared 3.3V and 5V rails. Just multiply and add the V x A for each line to get the combined output of the two rails. 200W or better is ideal, but even still, a low quality PSU will suffer from the problems you're seeing when under load.

Most here prefer Antec TruePower line PSU's. Search over in hot deals if thats the route you wanna take for nice prices at Amazon. I've also heard excellent things about the new Enermax PFC PSUs from knowledgeable users here.

Chiz

 

[RAndersen]

Thanks again... The ratings on the PSU are:

+3.3v = 28A
+5v = 30A
+12v = 15A
+5vsb = 2A
-5v = 0.3A
-12v = 0.8v

They actually don't look to bad, but I'm sure the regulation is poor... I'll look into getting something better.

 

[Shimmishim]

www.directron.com

find the fortron 350W one it's a great PSU and it's pretty cheap

yes, the truepowers are great as well ... at least 430W