Calibrating a CPU diode

[pHaestus]

Ok there has been a fair amount of discussion on the forums of late regarding making diode readings a bit useful. Since I have been idle on the site for a while, I decided to quit screwing around this evening. I soldered some copper twisted pair wire to the DXP and DXN pins of my 1600+ CPU directly. Yes you read that right. I have some familial obligations at this moment, but later tonight I will see if the chip still works. If so, the next step is to calibrate vs a Digitec 5810 in water baths using my MAX6655 evaluation system (0.125C res). Here's an obligatory pic:

http://www.procooling.com/~phaestus/drastic.jpg


I used a rubber band to hold the CPU onto a heatsink to hopefully help it withstand the heat a bit better.

Update later tonight...

[pHaestus]

The diode still works:

http://www.procooling.com/~phaestus/max6655.jpg

It is external sensor #1

I'll have to cut up my socket to actually install the chip; that is a project for later tonight. Then I will do a calibration tomorrow. I wish I had a constant temp bath.

Thanks to BrianS and KnightElite in the Pro/Chat for giving me the confidence to do this :)

[KnightElite]

Good to see the diode lives, unlike the one in my XP1600+ ;).
Hope the CPU still works also.

Pretty hardcore mod, indeed.

[BillA]

hey !
good stuff

I'll lay you dollars to donuts you can't raise the coolant temp (inlet to outlet) 0.25°C at 1.0 gpm

[pHaestus]

The CPU still works! I tested it out by putting some more wire under the corners to hopefull keep it kind of level and then putting the heatsink back on. It booted up and then started crunching K7Burn without issue:

http://www.procooling.com/~phaestus/testrun1.JPG

I am going to have to modify the socket to use this CPU since wires are sticking off of it, but it shouldnt be a huge problem.

More to come after a calibration attempt. I am guessing getting stable water temps will now be my next challenge...

[BillA]

for the purpose of calibration, I don't see the absolute constancy of the coolant temp as a big issue
unless of course you are trying to relate the CPU temp to the coolant

I would suggest putting the whole shebang in an enclosure, w/o circulation but filled, and plotting the readings over a range of temps
- the real difficulty with this is that the 'lag' of various parts will be diffferent so the determination fo equilibrium is crucial
(now the problem is holding everything at various temps to establish such)

you cannot have any temp differential between the CPU and the coolant temp/inlet sensor or you will have the whole host of temp offsets across the chain to deal with
- zero heat flux during calibration

I am assuming that everything is going to be 'calibrated' against (wrt) the coolant inlet sensor

[bigben2k]

Congrats pHaestus, I'm glad to see you were the first to take the plunge!

Now maybe you can write an article, as a follow up to your previous one, so that the rest of us can mod our rigs to measure temps more accurately (at least those of us stuck with a mobo that tries to read the CPU diode).

This could become a ProCooling standard, for anyone who posts a claimed temperature.

[BillA]

Ben

did you disconnect YOUR CPU ?
the one between your ears ?

did you read pHaestus' posts ? and mine ?
clearly you missed the nitty gritty

pHaestus is using a Digitec system with 0.01°C resolution
- please name a single OCer with that kind of capability
given that a 4 to 10 fold greater measurement capability is needed than the achieved accuracy,
we can assume that pHaestus will attain a solid 0.1°C accuracy

and thats the hardware end of it:
calibration - just who is going to do all the work that pHaestus is just beginning ?

or are you (NOT) thinking that the values derived by pHaestus will be 'valid' for everyone ?
arrrgh

I sure hope you never define "ProCooling" standards, we will all need Plexiglas bellybuttons

[pHaestus]

The big problems with others reproducing this are:

1) My diode reader is not of the DIY variety, but instead is the full package from Maxim on pcb connected to the parallel port of a second PC. This gives me the "extra bits" from the 6655 for 0.125C resolution. Not many will want to drop $100US for the package (though it is a very nicely made setup).

2) When you turn the CPU over and get out the soldering iron, you tend to lose your nerve. If you get the pins too hot, you will kill the diode. If you get the core itself too hot, you'll kill the chip. Your iron may not be grounded and so ESD is a concern as well. Not to mention, it is pretty ****ing insane to just start soldering copper wire to the CPU. To top it all off, when you are done then you have to hack up the top part of the socket to make room for the wires.

I can't really see anyone else doing something like this. The whole time I was getting the nerve to do it, I was thinking about how STUPID an idea that it was.

[bigben2k]

was refering to this article (http://www.procooling.com/articles/html/reading_from_amd_s_thermal_dio.php), which allows Joe user to measure the CPU temp.

Since then, diode reading has been added to most mobos, but this prevents us from doing that mod, because having two readers on the same diode gives an incorrect reading.

With what pHaestus has just done, that article can now be updated/expanded so that we can get back into measuring CPU temps to the closest thing to accurate that the average Joe can get. As for calibrating, it would be possible to include a procedure for that too! It'll be rough, but it's still a vast improvement to the +/- 10 deg C variance we're encountering.

Now do you see where I was headed?

[bigben2k]

Oh, I don't know, maybe I'm just way off...

I for one certainly would jump at the opportunity to do this mod.

[pHaestus]

Someone in the other thread gave a MUCH more elegant solution to people with faulty diode readings or COP instead of a proper diode reader.

Use desoldering braid to remove all the solder from the diode pins on the backside of the motherboard. This will break the connection with the onboard reader. Then you solder the wires of your maxim reader to the remaining socket pin only. I would do this 10x before I soldered on a CPU directly once.

I don't want people to get the impression that this was a "safe" or "smart" thing to do at all. It was a retarded idea but drastic measures were required to get me where I needed to go with diode calibration.

[BillA]

never any doubt about your direction Ben, nor any argument with its desireability
but you must temper your 'hope' with a realistic technical assessment of all the tools at your disposal
vs. those necessary to achieve the task

flying involves more than flapping the arms

[bigben2k]

Well now see, I thought that the desoldering option was ludicrous, and I for one, preferred your wire-wrapping suggestion. Otherwise I agree, soldering directly to a CPU pin is something I'd avoid.

For the benefit of everyone else, here (http://forums.procooling.com/vbb/showthread.php?s=&threadid=5718)'s the other thread.

[Brians256]

Congratulations, pHaestus! I'm glad I could lend a couple of kilograms of brass for your growing family jewels. Thankfully, the pins you were soldering to weren't in the middle of other pins!

[Since87]

Originally posted by pHaestus
Use desoldering braid to remove all the solder from the diode pins on the backside of the motherboard. This will break the connection with the onboard reader. Then you solder the wires of your maxim reader to the remaining socket pin only. I would do this 10x before I soldered on a CPU directly once.

I don't want people to get the impression that this was a "safe" or "smart" thing to do at all. It was a retarded idea but drastic measures were required to get me where I needed to go with diode calibration.

I'm not clear on how you are going to isolate the diode pins from the socket pHaestus. Cut them down so they don't reach?

Speaking from a lot of experience, I'd say using the solder wick on the MOBO is likely to be more challenging for most, than your technique. It's not necessarily easy to get enough of the solder 'wicked' out of the hole to have a clear separation between pin and hole. And, even when you do have a clean separation, unless you fill the gap between hole and pin, there is a risk of the pin making contact with the sides of the hole. (Pressure on the wire when you mount the motherboard.)

It looks like you used 24 gauge wire out of a Cat 5 cable. You could make it much easier on yourself with 30 gauge 'wire wrap' wire. I don't know if you can still get such at Radio Schlock, but any real electronics store would likely have it. (I'll send you 5 feet of it along with 36, 40 and 44 gauge magnet wire if you think you might want to try this on a different CPU.)

I think you are overestimating the risk of damage due to heating from the soldering iron. There is going to be a lot of copper to spread the heat between the pins and the die itself.

The difficulty in doing this is largely a matter of perspective. There are a couple ladies sitting less than 50 yards from me who wouldn't even bat an eye if I asked them to do either of these techniques. (Other than to give me a look of, "Oh, you screwed up and now we have to suffer the consequences." The answer to that is to come bearing chocolate chip cookies.)

[jaydee]

I am courious why you cannot just solder the wires to the backside of the mobo instead of the CPU itself?

Here is an example of the multiplier mod, but why couldn't you use the same mathod for this?
http://www.lostcircuits.com/cpu/amd_unlock/1a.shtml

[bigben2k]

JD, the problem is that when you add your own reader, your readings will be thrown off by the onboard reader (if your mobo has one).

[Since87]

The MOBO's temp measurement circuitry will interfere with the circuitry pHaestus is adding.

[jaydee]

Ok, so he cut the pins off the CPU so they will not connect to the mobo? Hummmm, I have a couple Epox 8K7A's that shouldn't read the internal diode. Would it work if I used the back of the mobo instead or are these connections still used for the diode under the CPU in the middle of the socket?

Now if you blocked this connection somehow will the mobo react wierd? Is there any monitoring in the bios that requires a connection from these pins or it will not boot, ect..? If not you could just cut the traces on the mobo, or dremel them out? I am up for destroying some stuff! :D

Sounds like a very interesting project. Might be cheaper than the die simulator I have in the works and you could test on a actual computer.

[Since87]

Originally posted by jaydee116

Now if you blocked this connection somehow will the mobo react wierd? Is there any monitoring in the bios that requires a connection from these pins or it will not boot, ect..? If not you could just cut the traces on the mobo, or dremel them out? I am up for destroying some stuff! :D


I've wondered about this as well. I wouldn't be surprised if some BIOS'es wouldn't let you boot with the diode removed from the circuit.

One advantage of doing things as pHaestus did, (I'm assuming he'll cut the CPU pins down.) is that a diode can be attached to the MOBO to keep the onboard stuff happy.

It might be possible to cut the traces on the MOBO, but there are multiple layers of traces in the PCB, and the odds that the connections to those two pins are accessible from the bottom are low. You might have better luck finding and cutting the traces near the diode reader IC. But then, if you do have to hook a diode to the diode reader to keep the BIOS happy, you may have a difficult time of it. (The pin spacing on the QSOP type packages these diode readers come in are are 0.025". Very tricky to solder a wire to an individual pin at that spacing.)

[murray13]

BillA's correct in one respect that the accuracy needed to measure temperature with certanty to less than one degree is beyond any average person. In water cooling a difference of 1deg C is a big deal. But most of us don't have a way of measuring a 1deg C difference. PERIOD. I'm really not going to get into all of the technical difficulty in doing it. Just say that temerature measurement is one of the least accurate basic things we measure. There are things less accurate but most are derived from the basics.

As an example we can measure:

Time +/- .000000000000005 sec
Voltage +/- .00000002 V
Mass +/- .0000002 kg
Temp +/- .00004 C

From NIST the people who calibrate the standards.

I personally don't care to know if I'm running colder than someone else. I agree it would be nice to be able to compare.

The only thing I can think of is using a ice bath. An ice bath is a insulated cup (styrofoam) filled with ice chips then filled with enough water just to cover. The ice and the water used should be pure not tap. Then while using keep stirring it. You can get 0 deg C +/- .1 to +/- .01 deg C using this method depending on your technique. In theory one could use this reference to see how much your temp sensor is off at 0 C. This correction can then be applied to all values. Realizing that most PN junction (diode) thermometers have a non-linerarity of about 1 deg C you can get close to being within 1 deg C.

Getting beter than 1 deg C readings is just well beyond what most enthusiasts will do.

[pHaestus]

The issue is not dealing with the motherboard's circuitry in my case.

Some observations:

The use of a diode reader tapped into SMBus just doesn't work for testing. I am seeing 5-10C increase in temperatures by booting the test PC into DOS mode and running K7Burn while monitoring the CPU temperatures with a second PC.

And what of calibration? What value is a diode reading without knowing how the diode deviates from the true temperature? So my major concern was:

Once you have a way to measure the diode temp, how can you calibrate it?

One could in theory put the whole system into a temperature-controlled chamber, adjust the temp, and then record what the diode reader reports vs. what the actual air temperature is. I lack this equipment or the energy to pursue this avenue.

Another idea is to calibrate the diode and reader vs. a much better thermometer in a water bath. By adjusting the temperature of the water over a fairly wide range one can MEASURE the error associated with the exact diode in the CPU you are using and with all your wiring. This is no problem since the CPU works fine as a diode without power. What IS a problem is that if you calibrate via one method (maybe wire wrapping to the pins) and then use a different method to actually connect the reader to the motherboard (soldering onto the socket pins) then your calibration is worthless. We are talking about resistances in the ohm range substantially affecting the diode reading. This is incidentally wh

Based on all of this, I decided to permanently affix the wires to the CPU pins. Now I can use the exact same setup (wires, CPU, reader) in calibration and in testing.

This was the only way I could devise to approach reasonably useful numbers for a diode reader.

Hope that clears things up...

[jaydee]

Originally posted by pHaestus
What IS a problem is that if you calibrate via one method (maybe wire wrapping to the pins) and then use a different method to actually connect the reader to the motherboard (soldering onto the socket pins) then your calibration is worthless. We are talking about resistances in the ohm range substantially affecting the diode reading.


I get it. The calibration process is what through me off.

[pHaestus]

Oh and jaydee I have put a diode reader on an 8K7A before via soldering onto the socket pins without incident. I DID have to tap into SMBus via the pins from a DIMM slot, but it wasn't a huge deal. I then just grabbed 5V and ground from the backside of the ATX connector and fired everything up no worries.

[BillA]

ok pHaestus, now I'm confused

how are you going to establish the difference between the CPU diode and the coolant inlet temp sensor ? (at say 25 and 30°C)

and how are you planning on establishing the (non) linearity of the CPU diode over the expected temp range? (25 to 70°C or so)

hell, I thought an insulated box was the easy way

[Since87]

Originally posted by pHaestus
What IS a problem is that if you calibrate via one method (maybe wire wrapping to the pins) and then use a different method to actually connect the reader to the motherboard (soldering onto the socket pins) then your calibration is worthless. We are talking about resistances in the ohm range substantially affecting the diode reading. This is incidentally wh


Another issue in addition to resistance, is the thermocouple voltage resulting from the differences in metals in the various conductors. I'd guess the socket pins are bronze rather than copper, and temperature differences between the pins will result in thermocouple voltages which affect the measurement. From the datasheet, "A 200µV offset voltage at DXP-DXN causes about -1°C error." It is important to maintain an all copper path from the CPU pins to the diode reader pins.

Soldering directly to the CPU is the only way to go if you really want accuracy.

[pHaestus]

I was planning on shrink wrapping the CPU and then dipping it in a water bath with a digitec thermistor in there as well and just varying the water temp to construct a curve for "diode temp" vs. "digitec temp" and then calibrate from that.

Bad idea?

[BillA]

simple is always better
sounds fine
don't spring a leak !

stir the bath, eh

[murray13]

BillA, everyone is just beginning to understand how much time and effort is involved in making accurate comparitve measurements.

Again my hat off to you for allready going down this road and not giving up somewhere along the line. Your temps are about the only ones on the web that I trust.

[Since87]

Yes, there is a lot involved in doing this right.

Thinking about this, a couple other things have come to mind.

First of all, solder flux. Most general purpose solder flux is somewhat conductive, and at the signal levels the diode reader operates at the conductivity is significant. Worst of all the conductivity will vary with humidity. It is important to get any solder flux off the CPU that could provide a conductive path between each diode pin and any other pin. I'd recommend using a toothpick to chip any large globs of flux off, and then rinsing with Isopropyl alcohol. (There are more effective flux strippers but I don't know how readily available they are.)

The second issue is the sensitivity of the circuit to EMI. It would be a good idea to put a ferrite core over the the leads between the diode, and the diode reader. (Similar to the lump you see in monitor cables.) This will greatly reduce the 'common mode' noise seen by the diode reader, while having no negative impact on its operation. Ideally the core would be located on the leads where they attach to the diode reader PCB. (I can send you a ferrite core for this if you wish.) It would also be a good idea to use shielded wire, with the shield tied to the ground of the eval board.

Sorry if I sound nitpicky, but I've got experience in designing hardware that is accurate to the 1 nanoamp, and 1 microvolt level. I'm very interested in the test results, and would like to see the test setup done right.

[Since87]

Just noticed that page 10 of the datasheet discusses some of the stuff I mentioned. The stuff mentioned there under PCB Layout and Shielded Cables must be given serious consideration in order to achieve quality measurements with the Maxim part.

[pHaestus]

Flux? From the soldering that I did? I didn't use any. I just went "balls out" and managed to get it right. I was planning on wrapping a floating ground (connected at the reader) all around the wires and keeping their length as short as possible. I guess a ferrite bead couldn't hurt anything though...

Many of the problems with the use of diodes are detailed in maxim's own technical documents and I am pretty familiar with those.

[Since87]

Originally posted by pHaestus
Flux? From the soldering that I did?

Most solder sold for electronics purposes has a core of rosin flux inside it. I was presuming you used such.

Edit: Considering the amount of error that can be caused by common mode noise, a ferrite bead could make a big difference.

[Les]

Bulit has done some excellent work on Diode calibration.*
Bulit's calibration** using a motherboard in a temp controlled chamber:
http://www.jr001b4751.pwp.blueyonder.co.uk/Bulit1.jpg

Maybe a word with Bulit*** would be useful

* http://www.ocworkbench.com/ocwbcgi/ultimatebb.cgi?ubb=get_topic&f=37&t=000245
Reported http://forums.procooling.com/vbb/showthread.php?s=&threadid=3957&perpage=25&pagenumber=5 with,then live, link to original calibration graph.
** This is a copy of Bulit's original. It is shown WITH PERMISSION.
*** http://home.attbi.com/~smithd/wsb/html/view.cgi-home.html-.html

EDIT: now "WITH PERMISSION"

[pHaestus]

Calibration HOPEFULLY tomorrow. I have a digital stir plate/hot plate at work I will borrow for the evening. I should be able to do a very good job in the 30-70C range with that (supposedly 0.1C accuracy but havent verified).

[Ace-One]

Be carefull about adding ferite beads. Maxim has a note (at least for the 1668 i use) about not using too much parallel capacitance (the small external capacitor plus the capacitance in the wires) since this will slow the rise times and result in inaccuracy.

Adding ferite bead will also slow rise-times and COULD be a problem.

I'd go with a pair of short twisted wires like Maxim recomends.

About the whole calibration thing, you could strap wour waterblock on the CPU and run hot water through it. When the CPU is not in the MB it does not give off heat, and it's temp should be very close to the water temp. Especially if you place it in a small styroform box or add other isolation from env. air temperature.
Then you can change temp by adding hot or cold water and make your curve.

[Since87]

Originally posted by Ace-One
Be carefull about adding ferite beads. Maxim has a note (at least for the 1668 i use) about not using too much parallel capacitance (the small external capacitor plus the capacitance in the wires) since this will slow the rise times and result in inaccuracy.

Adding ferite bead will also slow rise-times and COULD be a problem.


No, if both diode leads go through the ferrite bead, only common mode signals will be impeded. The differential mode signal is unaffected. (Common mode signals are common to both leads. Differential mode signals are the difference between the signals on the two leads.)

The diode reader (ideally) only measures differential mode signals. In actual practice, the accuracy of the diode reader is affected greatly by common mode signals.

The value of twisted pair, is that becuase the leads are kept close to each other, the signal picked up from EMI will be predominantly common mode. Using twisted pair to limit noise pickup to predominately a common mode signal and then adding a ferrite bead around BOTH leads minimizes the impact that EMI can have on the measurement.

Because the diode reader's response to noise varies with frequency, it is very important to minimize this source of error in an environment where the ambient noise may vary in frequency from one test to the next. (e.g. a cpu that may be clocked at various different rates.)

pHaestus,

I just got the ferrite beads mailed today. I also included some shielded twisted pair wire and some extremely high permeability amorphous metal cores. The amorphous metal cores are a bit large though. I'd recommend using one if space is not too much of a problem.

Edit: grammar

[pHaestus]

One of the wires came off today when I was setting up to calibrate. When I resoldered it on, I managed to knock off two pins to the chip. One was the diode's DXN; the other one is a vcc pin. Not sure exactly how, but CPU still is running fine and crunching Prime95 now. The diode pin is ruined though. I still have the other pin and will try to resolder it on when I hit upon a good plan for doing so.

I have another 1600+; I am debating the foolishness of trying this a second time.

[Since87]

If you want to ship it here, I'll do it. (Or more likely, get one of the aforementioned ladies to do it. Got any chocolate chip cookies you can pack with it?)

I'm not too surprised the damaged one still operates. The Vcc pins are all tied together inside the part. Losing one Vcc will just increase the total resistance from Vcc outside the chip to Vcc inside the chip and give the CPU a slightly less optimal path to the capacitors on the substrate. It probably won't overclock quite as high as it would have with all its Vcc pins intact though.

[pHaestus]

You know I think I am going to take you up on that. E-mail me the info and I will try and scrounge up some cookies :)

phaestus@procooling.com

[pHaestus]

I finally got around to redoing the wiring today and I did it properly this time:

http://procooling.com/~phaestus/progress.jpg

I tested it out on the max6655 and it still works as a diode at least :)

I have a Fisher hot plate/magnetic stirrer at work that is digital and accurate to 0.1C (yes it was expensive). I will bring it home tomorrow along with a stir bar and calibrate from 25C to 70C in 5C steps with constant stirring.

Hopefully I can get my A7V-133 back from KnightElite tomorrow too and verify that the CPU still works :)

[KnightElite]

Hmm.... I still don't have my computer hardware back :(.

[pHaestus]

ok KE I will calibrate the CPU using a water bath and the DIgitec today and then if possible get my GTower from you on tomorrow. Seem reasonable? Put some tracking search on that mofo!

[pelle76]

Question1:

When people say that the diode reading on mobos suck... What is it really then that sucks??

-Is it a problem that the mobo has cheapo diodereaders and therefore returns a nogood value...

-Or is it the problem that the diodes on AMD CPU:s are not uniform from CPU to CPU???

Question2:

Can I remove the two diode pins from my CPU and it will stil work???


Idea:

If the first assumption in question1 is right. (The mobo diode reader is crappy) and the assumption in question2 is right. Then I'm going to do like this.

-Take my cheap backup Duron1300. Remove the two diode pins. And put it in the socket.

-attach (not solder) two wires to the back of my ordinary CPU. The other ends goes to the back of my mobo to the pins for measuring the CPU diode.

-Fire up the computer and put my ordinary CPU with its pins in a waterbath with an externam thermometer telling me the water temps.

-Waiting a while to let the CPU get the same temperature as the water I can now compare the temps my mobo gives me and the temps of the water.

Not very accurate... But would this work???

[hara]

-Take my cheap backup Duron1300. Remove the two diode pins. And put it in the socket.

Durons don't have internal diodes :(

[pelle76]

Originally posted by hara
Durons don't have internal diodes :(

Great... Then I wont eaven have to take those pins off...

Will the rest of my idea work???

[pHaestus]

Morgan core Durons have an internal diode.

You can't just "attach" wires and expect reliable readings because you are going to get a lot of resistance on the connection which will screw up the reading. 1ohm resistance lowers the reading from 0.2 to 0.4C I believe.

I will at some point soon report the calibration tests and a full rationale for why I chose the path I did. You should read the article on diodes I wrote for this site in the meantime.

[nexxo]

Unregistered: just off-topic for a moment: what brand of coffee do you drink? :p

pHaestus: nice work!

[pelle76]

Originally posted by pHaestus
Morgan core Durons have an internal diode.

You can't just "attach" wires and expect reliable readings because you are going to get a lot of resistance on the connection which will screw up the reading. 1ohm resistance lowers the reading from 0.2 to 0.4C I believe.


I know... As I said... "Not very accurate"

But appart from the accuracy... Would it work in theory...

And if my Duron has a tempdiode. Can I just remove those legs or will that screw up something else with the CPU???

[pHaestus]

You can take them off; I have an XP missing a couple pins from my first go at soldering. Still works fine. I might try something else tho like opening up the socket and just pulling out the diode connectors from the top instead. That way you don't damage chip.

Do you have an Asus mobo with the COP protection but not full diode temp readings? I am not sure why one would bother with lots of modification when the mobo already measures the diode. I just left my 8K3A stock; works fine.

The stuff I am doing is way out there for testing; I don't see where it is needed for average Joe types...

[pelle76]

Nope.... Ive got Epox 8rda+... Everybody says they suck at measuring the dietemp... So I figured I would Ust try this to see If it is faar out there or if it seems sound...

[Brians256]

Question1:

When people say that the diode reading on mobos suck... What is it really then that sucks??

-Is it a problem that the mobo has cheapo diodereaders and therefore returns a nogood value...

-Or is it the problem that the diodes on AMD CPU:s are not uniform from CPU to CPU???


I can't say for sure what all people mean when they talk about the diode reading. However, I can talk about some of the problems with the diode temperatures reported on some motherboards.

1. All temperature probes report the temperature of the probe, not the object you are trying to look at. So, the temperature is always the temperature of the DIODE, not the overall CPU. How this comes into play is when different portions of the CPU are hotter than others. So, the diode may be reading a dandy 27C, but another portion of the CPU just reached 40C. The solution would be to place multiple diodes within the CPU and support an SMBus protocol to read the temperature throughout the different regions of the CPU. I don't see that happening anytime soon, though.

2. Diodes are different in different CPUs. We read the temperature by sensing the voltage drop across the diode given a constant current source, but each batch of wafers is a bit different. When you are sensing millivolt differences, a minute production change makes huge swings in reported temperature. This can be fixed by a calibration procedure such as pHaestus's procedure.

3. Different motherboards implement non-optimal circuits to read the diode temperature? This is an unknown, but there was a rumor that some motherboard manufacturer (I can't remember whichone) didn't implement the circuit according to spec, so you got a non-linear offset.

4. Temperature readings depend heavily upon low impedance and noise-free connections to the thermal diode. This is what pHaestus is alluding to when he states that "you can't just attach" to the CPU diode. If your connection between wires and pins is not very good, you will create resistance and capacitance that will give you bad temperature data. Fix? Use high quality wiring soldered to the CPU pins. High quality means twisted pair and as much copper as you can reasonably fit in that space (although 22 AWG should probably be as much as you'd benefit from).

5. Diodes don't react instantaneously. This is related to item 1 in that a wild temperature swing in one portion of the chip will take time to propagate to the site of the thermal diode. This is not a large issue with our type of testing, but it is important for any circuit that would allow the Athlon to safely boot and/or run without a heatsink, for example. Removing the heatsink from a running Athlon might destroy critical transistors before a diode could react to the increased temperature.


Question2:

Can I remove the two diode pins from my CPU and it will stil work???


I think so. Your motherboard may not run though. Your motherboard might have a failsafe that senses that condition as a fatal error. If the diode pins aren't present, it could appear to be a thermal runaway issue to the motherboard, and the safeties might kick in.

Short and accurate answer: dunno.


Idea:

If the first assumption in question1 is right. (The mobo diode reader is crappy) and the assumption in question2 is right. Then I'm going to do like this.

-Take my cheap backup Duron1300. Remove the two diode pins. And put it in the socket.

-attach (not solder) two wires to the back of my ordinary CPU. The other ends goes to the back of my mobo to the pins for measuring the CPU diode.

-Fire up the computer and put my ordinary CPU with its pins in a waterbath with an externam thermometer telling me the water temps.

-Waiting a while to let the CPU get the same temperature as the water I can now compare the temps my mobo gives me and the temps of the water.

Not very accurate... But would this work???


If you wish to use an external circuit, you'd be better off cutting motherboard traces than removing CPU pins.

Other than that, it looks like it might work.

[pelle76]

Thanx Brian256

I think I will try my idea... Ust to see if it comes out a little bit right :)

[pHaestus]

Might try wrapping the pins in teflon tape instead of cutting them.

I didn't even know the newer Epox mobos read from internal diode. I know they had for a while done away with that after 8k3a...

[KnightElite]

pH, AMD's specifications require all newer motherboards to read from the diode. My friend was pissed off because the ASRock board he bought didn't read the temperature of his T-Bird, since Asus didn't bother putting an in socket thermister into the board at all.

As to getting your system back, I suppose I will have to let you have it :D.

[pHaestus]

No AMD spec is for all motherboards to have the ability to shut down if the diode temp is too high. Many mobo makers use the diode for this but still take temps with an insocket thermistor. Sad but true :/

[jaydee]

Originally posted by pelle76
I know... As I said... "Not very accurate"

But appart from the accuracy... Would it work in theory...

And if my Duron has a tempdiode. Can I just remove those legs or will that screw up something else with the CPU???
If your not going for accuracy then why bother?