THERMAL DIODE MOD

THERMAL DIODE MOD

Updated 05/11/02 by Tim B @ OCWorkbench.com

Original Thread By Bullit
http://forum.ocworkbench.com/ocwbcgi/ultimatebb.cgi?ubb=get_topic&f=27&t=002639

By Bullit
This note requires exacing soldering skills and is meant for persons who are familiar with and capable of soldering to the leads of a PQFP IC package (.050 inch lead spacing). If in doubt then don't attempt this mod to your board!!!!! Any incorrect wiring or soldering could have VERY BAD CONSEQUENCES!!!
I have found a way to monitor the Core Temps of second generation Duron and Athlon MP and XP processors using the first temp sensor input of the onboard IT8705F monitoring chip. The case ambient temp and under processor temps are already monitored on inputs 2 and 3 respectively.

Data sheet for the IT8705F is here:
http://www.iteusa.com/productInfo/Download.html#IT8705F

AMD thermal monitoring spec is here:
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/24228.pdf

Arctic Silver thermal diode compensation spec is here:
http://www.arcticsilver.com/diode_calibration.htm

This is how to do it.
1)solder a 30,000 ohm resistor (use a precision resistor if you can get one to limit thermal drift) from TMPIN1 input to VREF output (pin 89 to pin 90). VREF goes to a couple of the resistors in that area so you can pick it up there.
2)Solder a .0033uf capacitor from TMPIN1 to GNDA (pin 89 to pin 86). GNDA also goes to several of the caps in the area so you can pick it up there.
3)connect a twisted pair of wires to GNDA and TMPIN1 and run them to pins S7 and U7 of the CPU socket on the solder side of the board. TMPIN1 goes to S7 and GNDA goes to U7.
4)Calibrate the thermal diode using the specs suggested.

I have access to the Analog Devices evaluation card and used it to determine the offset required to calibrate my processor's thermal diode. I had to subtract about 4 degrees c.

Run the latest version of MBM and configure the temp input 1 to be a thermal diode. Add your calculated offset and you're ready to go.

Be advised that the AMD processors thermal diodes are reported to be somewhat nonlinear.

While this process is not perfect at least the internal temp can be monitored and is useful for comparisons of cooling modifications and processor loading.