XP-Diode reading fails, does Maxim 6657 need an offset!?
 

Hi! I just assembled such a Temp-Reading-Circuit described on many sites like http://www.procooling.com/articles/h...hermal_dio.php

I'm sure having assembled it properly, but the remote sensors shows over 100ºC in MBM5!!! The local sensors is right (28ºC). :mad:

The remote wire is shielded and 4in (10cm) long. I also but the filter stuff correctly (2.2nF for the sensor, 2x 100Ohm resistors & 2x100nF for supply) :shrug:

So, has anyone got it working?

What might be the cause?

Do I have to set an offset for the remote sensor?

Got the connection to the thermal diode backwards? MBM would say 127 for that.

Have a diode, any diode, or maybe a diode-connected 2n3904 transistor that you could connect to that input channel to see if its working?

Quite sure it's not backwards.

Further, den Temp is increasing under load. Looks like a DC offset.

I have a Thoroughbred-B 0.13µm Athlon XP1700+. Maybe a different diode than Palmino?

The diode idealty factor is a bit different between the the two, but that wouldn't account for more that a degree or three.

Series resistance is another possibility.

That's right. I guessed that. But I hate these disassemble-the-computer-reassemble-the-computer-without-success-cylces..... ;)

Right. I soldered a SI-Diode (1A, didn't find a smaller one) and I shows 112ºC. Touching it with my hand increases the Temp.

This means that the remote channel has an offset of 87ºC, as the local sensor shows 25ºC.

Finally: the diode reader says -127ºC when connected backwards :D

Your SI-Diode will have a rather different ideality factor than the reader is set up for, so I wouldn't use it a calibration method. A diode connected 2n3904 very nearly matches what's in the CPU.

So, what's between the IC and that diode? Eliminated any possible series resistances? Checked for duff solder joints at the IC? Followed proper static-electricity safeguards?

no duff solder joints, used 4in of shielded cable, 2200pF condensator in parallel close to the IC

I will try the other sample MAXIM sent me. Lets see....

Broken wire in the cable?

Could have been heat damaged during soldering???
Its been a while since ive used MBM and i cant check coz i dont have it installed but i remember a while back when i was using it i had to change a pulse timming setting or sumpn so it detected one of my fans correctly, it was giving an increadibly high RPM reading, hope this helps :)

I soldered another MAX6657. Same old story!

I took a lot of care not damaging it through heat. Maybe it's MBM's fault.... (Version 5.3.6.0)

The cable is definitely not broken. No series resitance (i.e. less than 0.7 Ohms).

:cry:

That is mighty bizzarre. I am at a loss. :confused: