Hi,

I have recognized that the "CPU Temp." sensor returns incorrect values on the X399 Taichi after updating the BIOS to the last version 3.20. The sensor simply returns 40°C at every condition. Therefore, the reported values will not change if the CPU heats up or cools down.

So, if the fan control is switched form "Tctrl" to "CPU Temp." the fan speeds will not change at all. In addition, it is irrelevant if the standard, silent, performance or custom curve is selected. The fan speed will be stuck at their 40°C value at any condition. The Tctrl otherwise acts as expected but unfortunately with the +27°C offset added.

furthermore, I have read related threads, e. g. for the x370 boards. It seems that they have this specific problem too. For what ever reason, it seems that a incorrect or faulty temperature readout is implemented on all AM4 and X399 boards. Either, because the Tjunction temp. isn't correctly obtained from the CPU or the on board sensor below the socket isn't accecces the right way (if ther is any).

If you have observed the same behaviour, please add your findings.

http://forum.asrock.com/forum_posts.asp?TID=9207&KW=cpu+temp&title=cpu-temperature-sensor-problem-on-asrock-x470-fata

PECI is wrong sensor i think

in HWInfo settings enable reading for negative temps. then i have one CPU reading (on motherboard) more but -62 or somithing like that. 

I noticed this issue on my x470 Taichi as well. Attempting to use "CPU" for the fan tuning resulted in the fans never changing speeds even when stress testing and the CPU temp raising. I don't know if I am just misunderstanding what value that is tied to and maybe it isn't hitting the breakpoints I am expecting, but it does not seem to work as expected.

I switched to using the tctl for the fan tuning and this seems to be working more as expected.

EDIT - Just in case this is a bios issue, I am getting this with v. 1.50. I can't say for certain if it was working prior cause I just built this machine and updating the bios was one of the things I did before really digging into the settings and testing.

Thank you!

I can also read the correct values from the CPU under windows with HWInfo64 - in fact for the Tctl and Tdie. I would assume the program simply subtracts the 27°C offset from the Tctl value here.

But, that is not the point here. The problem is that the BIOS  will not control the fans by the "CPU Temp." correctly. Therefore, we have to switch to the Tctl in the bios. Unfortunately this value is too sensitive to load changes such that the fans will ramp up and slow down like crazy.

Well it is definitely broken. Because having a control function that relies on a temperature value that won't change makes no sense.

I could imagine that the engineers want to implemented a function here that realizes some kind of filtering to reduces the slope of the fan cure or at least some kind of hysteresis. But it seems that this implementation is broken, providing 40 ° C for "CPU Temp" at least within a human-perceivable time span.

I had been assuming that my board was broken but maybe this is a generic problem.  Very strange.

(PS I seem to recall that at least for the X470 Taichi BIOS, you can't select Tctrl in the cute FanTastic graphical thingie, but you can select it in the tabular layout.)

BIOS is whatever the early-July Taichi update was.

Yeah, I'm hoping this issue gets fixed as well. I'd very much prefer that my case fans are observing CPU temp instead of TCTRL but if it can't monitor the temps effectively, it's kinda pointless.

ASRock X399M Taichi here.