?? Phase Change LN2 ??

[firstdegreeab]

This might be a really stupid question, but why can't we use the same phase changing principals (single or cascade) on nitrogen??? I'm a total newbee to phase change, only reading forum's articles. Just a thought, PS i'm also lacking lots of sleep, but who here isn't. haha

 

[crotale]

Theoreticly, you can. But the machine would cost a fortune to build, and there are almost no CPUs that can handle the cold.

It is far easier to just pour LN2 into a copper container on the CPU.

 

[firstdegreeab]

Thanks for the quick resonse. Why do you say that most cpu's can't handle the cold, don't lots of people make ln2 pots? I know that this is for short duration but is it too cold for longer durations?

 

[greenmaji]

think of phase as refigeration and ALL levels of freezing.. ln2 is made by using a very complex multi stage cascade phase machine freezing NO2 gas.. I have only seen two attempts and building a cascade big enough and complex enough to hold -200C temperatures, one there honking huge, two they take kilowats to power, three they have been atempted and not yet done by cascade MASTERS, four its hard enough to get the gas needed build a single stage, five its just too dammed complicated comparied to using a pot and ln2

btw. if it made sence to use a cascade like that, crotale would most likely have one or have acess to one..

 

[crotale]

Thanks for the quick resonse. Why do you say that most cpu's can't handle the cold, don't lots of people make ln2 pots? I know that this is for short duration but is it too cold for longer durations?

When we bench with LN2 we don't fill up the entire container. We just pour a little bit in it from time to time to keep the base temperature at a certain level, depending on the CPU. CPUs today coldbug anywhere between -15 and colder, so first we just find this level and then benchmark around it.

 

[firstdegreeab]

glad i threw it out there. Just wanted to see why.
thanks for the responses. Are the cold bugs more prominent in amd vs. intel???

 

[El<(')>Maxi]

crotale,

Can you tell me how often you have to pour to keep a loaded chip in the zone?? I have always wondered about that.

 

[Gautam]

When we bench with LN2 we don't fill up the entire container. We just pour a little bit in it from time to time to keep the base temperature at a certain level, depending on the CPU. CPUs today coldbug anywhere between -15 and colder, so first we just find this level and then benchmark around it.

Another question- at what temps did you run into the cold bug with the Preslers/Cedar Mills, if you did at all?

 

[El<(')>Maxi]

Mike said he hit bugs on all of his Preslers basically limiting FSB.

 

[Ross]

Are the cold bugs more prominent in amd vs. intel???

There is no question that AMDs are the cold bug king

Mike's Preslers stopped booting/running at some temp or they just wouldn't OC any further? There's a big difference between not working under -"x"C (cold bug) and just not clocking any higher no matter what I think past a certain point on these, colder temps just aren't going to do much or anything for increasing clocks...I don't think that's a bug, I think it's the limits of the cores.

 

[Gautam]

No, Mike had very severe difficulty in running his 955XE's on dry ice. 5 gigs easy on air, yet the highest speed he hit frozen AFAIK was "only" 5.8GHz. Crimedog and Fishy also ran into a bug with Crimedog's 631. I know some Dothans are also bugged, though not till around -100C...but that's "hot" enough to hamper clocks when you're on LN2. Unfortunately, it seems that the cold bug is inescapble as modern procs are made on finer and finer fab processes.

 

[El<(')>Maxi]

Mike's problems we're under LN2 and limited him to under 300FSB or something like that. I think it's safe to say that Intel chips are less affected by extreme temps

 

[Ross]

"Cold bug" to me means that a proc won't work at all under a relatively low -C, like -15C. I don't think anyone could call issues at colder than -100C a "cold bug"

I've said a lot of times that CedarMill cores seem to be 1) stable pretty close to their suicides for any given cooling and 2) don't respond drastically well to substantial decreases in temps. The latter is particularly true on Preslers. If they are pretty good on air or water, that's really the telltale sign if it's a good clocker at all.

For me stock cool air->cool water was 200-300MHz more. From cool water->phase was also only 200-300MHz and that was a huge drop in temps. From phase->DI (20-30C less than phase with a lot more capacity) also gave 200-300MHz, but that was a lot of work and trying for over an hour. Stable gains on DI were more like 150MH with a constant feeding of DI for even that. Even at idle, DI was not enough capacity to keep the temps from running away > 5.8GHz/1.70Vc with the proc *idling*. There's a very good reason any Presler screened >6GHz is pretty much guaranteed to be running on LN2

I really don't know what crime/fishy's issue was on the 631...I am still not 100% convinced it was a cold bug. I've run across issues that might mask themselves as that...like tightening the evap too much and bending the board just a bit too much. For a week until I figured it out, it would boot OK when "warmer", but after it idled a bit and cooled off more, it would lock up and then not reboot unless I let it sit for a long while. Turns out that board was bent "just enough" to be fine when warm, but when things cooled off more and contracted, it would cause a problem. I loosened the mounting screws 1-2 turns each and the issue magically disappeared. To this day, I tighten the evap until it won't POST and then back off 1-2 turns on each screw...that's how I know when it's tight enough, LOL.

Lastly, I've see really strange behavior on CM cores. Even ones that can do much better than mine on air don't do any or much better on water. I mean I've seen Preslers that will do upwards of 4.6-4.8GHz at default Vc and mine needed Vc starting around 4.2GHz IIRC. That clearly seems stronger than mine, yet they still cap out out in the same 5.0-5.2GHz range on water, just like mine.

I dunno, I still think it's the proc limits. All but the strongest CM cores seem to start running into trouble around 6GHz +/-200-300MHz regardless of cooling. Seems like 6.2GHz+ is limited to the best cores on the best cooling at that. That problem is compounded on Presler since BOTH cores need to be gems.

FSB is definitely an issue too for heat/stress. All the XEs that are much >6GHz are not only doing it on LN2, they are at extremely high multis (low FSBs). My guess is they can't possibly do it any other way...just too much stress.

 

[Gautam]

Waiting for Mike and Crotale to give us a reply themselves...it looks to me like it kicks in at around -60C in some cases, which is too hot for LN2 and cascade as well in some cases.

 

[Joe Camel]

here is a quote from PC Ice on the cold bug subject...(about a month ago)

i just tested a few FX57's and found that they can take up to -70c with out the cold bug kicking in.

(we were discussing custom units in PM over on on XR)

 

[Ross]

JC, we're talking Intels

Yes, someone that's run colder than -80C on a CM or Presler, speak up The lowest mine reads on DI is -63C. It may actually be a little off since I am measuring with a probe on the side of the IHS. Either way, I haven't had a single issue on either the CM or the Presler yet.

 

[mikeguava]

Hi all,

yes there are some coldbugs that are affecting Preslers - at least with ES 955 and ES 950s that I had been testing. I along with 3 other freezing people combined went thru something like 15x Presler ES cpus and out of those 15 - 12 showed mayor boot problems between -36C ( 8 of them) and -80C ( 4 of them). These CPUs would not boot at core temps below that at all.

3 of the 15 would boot and run at any temperature.

On the other hand all of them were able to go significantly colder once running. Most of them actually as cold as your cooling was able to go. This particular coldbug was only a boot bug per se.

Another problem that we run into that hasn't been properly been researched on at my end -- is FSB limitations under extreme cold.
While I could run a 955 @ 6.6GHZ -140C - I was not able to do this with high FSB - I had to go with a high multi and low FSB to reach these clocks.

AFter a little bit of testing I found out that by lowering MCH and other voltages I managed to get higher FSB clocks while under cold - but I haven't yet had the time to really look into what was causing the FSB coldbug and how it could be combatted.

I know that Crotale and Fugger have both managed ot get reasonable FSB clocks ( ~ 320- 340) - yet neither of them either were able to run their max FSB as well ( ~400).

EDIT: Just to thorw this in - I have a feeling that the low FSB codbug has to do with the 975X chipset and not necessarly with the CPU. Again just a hunch - need to look into that in the near future

here is a quote from PC Ice on the cold bug subject...(about a month ago)


(we were discussing custom units in PM over on on XR)

Please keep in mind that EVAP temps and CORE temps are vastly different - - there is NO FX57 that can take -70 core temps. Depending on many factors a -70C Evap temp can still result in a -35C core temp - which is well outside of many FX57s coldbug territory.

 

[{PMS}fishy]

Mike said he hit bugs on all of his Preslers basically limiting FSB.

I'm pretty sure we hit 2 cold bugged CPUs as well.

 

[mikeguava]

crotale,

Can you tell me how often you have to pour to keep a loaded chip in the zone?? I have always wondered about that.

Just a very rough answer to that from my experience - with no coldbug cpus you need to poor a certain amount every 20-40 secs - with coldbugged cpus ( like a FX60) every 5-10 secs.

With coldbugged cpus - you benchmarking is mostly focused on wtahcing temps - I caught myself many times missing the fact that I had already crashed - yet was still lost in pouring and monitoring...

 

[Ross]

Thanks for posting Mike! I was thinking maybe the HT on the 955s were possibly causing more of an issue, but if it's happening on 950s too I guess that's not it. The real common denominator there is they are ES. You certainly don't see issues like that in that kind of frequency on lower, retail versions and there certainly are plenty running -30C or colder. Are all of those cold bugged ESs coming from the same source/batch?

I know that Crotale and Fugger have both managed ot get reasonable FSB clocks ( ~ 320- 340) - yet neither of them either were able to run their max FSB as well ( ~400).

Yeah, I've thought that was my issue on the 930 since the first time I put it on DI. I need exactly 400FSB for 6GHz on it and just doesn't want to do it. In fact, pretty much anything over 385FSB or so is where it gets really bent out of shape. If I had this core with like 16-17x multi available, 6GHz would probably be a *lot* easier. I am waiting to see what the C1 steppings do and may try a 940. In either case, I guess I'll stay far away from 950-960s, XEs and ESs

AFter a little bit of testing I found out that by lowering MCH and other voltages I managed to get higher FSB clocks while under cold

I've posted the same thing previously and this seems to be a CedarMill core phenomona (wasn't a problem on my Prescotts), but my CMs and Preslers seem to be much happier with lower Vmch. I am actually contemplating removing my mod or replacing with a higher resistance pot to lower it more (min = 1.74V actual with the pot I used).