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How to connect on-die CPU temp diode to 2-pin thermal sensor connector?

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Old 04-15-01, 04:36 PM Thread Starter   #1
Karsta
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How to connect on-die CPU temp diode to 2-pin thermal sensor connector?


I have PIII 700E (FCPGA) which is connected to ASUS P2B-F with ASUS S370-133 CPU card (supports thermal monitoring). I would like to use the on die thermal diode to measure the CPU temperature but the Winbond W83781D on P2B-F is connected to two 2-pin thermal sensor connectors.

Inspite knowing very little about electronics or about the risks of the operation, I attached leads between B14/B15 of slot 1 and mb thermal sensor connector. Results were not good: bios reported 0 degrees Celsius and MBM5 -42.

Is it possible to build a functional circuit between B14/B15 of Slot 1 connector and the sensor connector on the mb?
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Old 04-15-01, 05:37 PM   #2
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intel uses a thermal diode in its chips, where as most temp sensors like the one you connect that lead to use thermisters, I'm not sure if they are the same or not but I do know diodes are one way electronic devices where as a resister shouldn't matter, try connecting the lead the other way round, if that doesn't work then I guess thermal diodes and thermisters are too differant, try buying a thermister (about 50c/p) and have the tip just touching the core but also make sure the heatsink doesn't crush the thermister and is in contact with the core correctly, you could buy a few thermisters and rig them up to a switch to measure several things, there is a guide for something similar to this over at OcMOD

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Old 04-16-01, 03:53 AM Thread Starter   #3
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I have a thermister in use for CPU temp currently. It is so large (maybe 3 mm thick and round) I can't get it in touch with cpu core. I'll try to buy a smaller one and drill a hole for it in the hs.

I also tried to switch the leads which gave constant -46°C.

Anyway the idea was to get the on-die diode in use and have the thermister for varying case temp measurements (there is one free temp connector on mb). I thought that it would give accurate real cpu temp.

Actually reading about MAX1617 (which Intel mentions as the thermometer to be used with PIII in the 440bx design guide) a bit opened my eyes about accuracy - manufacturer promises ħ3°C for remote accuracy. More than that there is lots of possible error sources (like CRTs, clock generators, memory buses and ISA/PCI buses) in routing the traces which can account for errors of +30° at maximum. I guess there is a difference in between routing traces on mb and drawing leads across mb but I could never know without calibration.
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Old 04-16-01, 03:37 PM   #4
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there are tmermisters that ar almost flat, they are usually orange and quite long, the one yo have sounds like the type that is used in the underneath of a socket, is it blue by any chance.

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Old 04-16-01, 03:58 PM Thread Starter   #5
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It has silver tip and rest of the visible part is orange if I remember right. It is self made and mainly covered with plastic sock to cover the solders. I have no idea of it's type but it works fine. One salesman at local compstore was kind enough to sell me his own (didn't need it anymore). Asus P2T-cables are a bit hard to get here in Turku Finland.
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Old 04-16-01, 04:27 PM   #6
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that sounds like the standard flat type that most people use to measure cpu temps, you should be able to have it taped to the green pcb with the tip just touching the core and be able to fit the heatsink on if it is, I'll try find a picture of how most people do it for you

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Old 04-17-01, 10:04 AM Thread Starter   #7
Karsta
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That would kind of you.

Currently I have it inbetween the green PCB of CPU and hs (it just fits in and holds nicely). Tip just touches the base of hs. Because the CPU rises less than mm above the PCB and the hs's base (GORB) is wide I can't get it in contact:

|____________hs________________|
................|____base______|O-THERMISTOR-
....|ŻpcbŻŻŻŻŻ |CPU| ŻŻŻŻŻŻŻŻŻŻ|

Hope this picture clarifies.
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