Core Voltage variations

[hydrogen18]

I have a core i7 860 that sits in my garage. The garage gets hot this time of year. I noticed CPU temps were getting above 50 C for the better part of the day.

I realized the cores were spending all day at 2.8 ghz. So I enabled Intel Speedstep in the BIOS. Now they sit at 1.2 ghz for most of the time. I also disabled fan speed control at the same time, so the CPU fan just sits at 3000 rpm. While I had the PC off I also blew some dust out of the CPU cooler (OEM) but it wasn't actually horribly dusty as the intake of the case has a foam filter on it.

However two strange things happened. After enabling speedstep, VCore started going all over the place. CPU temperature wasn't much lower. Then suddenly VCore leveled off completely and the CPU fan speed started changing. I don't think this should ever happen.

Here are graphs of the data over the past 24 hours. The gap in the graph is where I restarted so I could change the intel speedstep in the bios.

GRAPHS

The PSU is a Seasonic unit. I don't remember exactly what one but it was top rated here on the [H], was like $170 and came with a 7 year warranty.

The motherboard is an ASUS p7p55d LE.

The cpu is a Intel Core i7-860 Lynnfield Quad-Core 2.8GHz LGA 1156 95W Processor BX80605I7860.

What exactly is going on here? The OEM cooler is the original one from when the CPU was purchased almost immediately after release, so I could see the fan going bad. But the fact that VCore just changed at the same point in time as well doesn't make any sense. The way I got the SeaSonic PSU is that I had an Antec unit that was apparently bad for nearly 3.5 years because during that whole time I could only get hard drives to last about 180 days before dying. Ever since that PSU died all my HDDs have been fine.

 

[Shadowdancer]

Speedstep and other automatisms in that area can be regarded as a black art, and as long as the system is stable, it's probably normal. Your board also has that wacko "EPU" feature that you should disable since it will only make any weird behaviour even worse by trying to dynamically fudge voltages as low as they go or until the system just fails.

However, all electronics also derate with temperature and most ratings you find will be at 25°C component temperature, in the case of semiconductor parts even junction temperature, instead of ambient. So basically a PSU and the regulators on the board will only work at specification at temperatures rather significantly below that unless each component is individually sunk into an appropriately large heatsink. Putting that stuff in a 50°C garage will reduce performance a lot and give any regulating logic and circuitry a hard time, so voltages may start to glitch and you really won't be able to draw as much power as any manufacturer printed on their shiny boxes.

 

[hydrogen18]

Unfortunately you may be right. For some reason the core voltage jumped to 1.3 volts! Then the machine went nuts, processes were dying, etc. After some fiddling in the BIOS I realized I can manually adjust the core voltage and multiplier. I set the core voltage to 0.85 volts and the multiplier to 9x. This makes it a quad core i7 @ 1.2 ghz, but this machine really isn't CPU bound anyways.

Also I swapped out the existing 120mm fans for 3x Delta FFBs which are insanely loud, but probably move 10x or 12x the airflow of what was in there. Its still hot air, but much more of it.