Fan control pwm problem

[Ark1375]

I have a Msi 870-g45 motherboard and an AMD Phenom 2 x4 965 cpu in my rig (I know, it's old). Lately I have this wiered issue that after like 30-45 min in the windows (I didn't check any other Os), no matter the amount of load on the cpu, the fan just drops to like 1000 rpm without any good reason(when loaded it suddenly drops from 5000 to 1000). The CPU gets hot and eventually the system shuts itself down because of the overheat.

I tried to mess with the bios settings for fan control but no change. 

There is this option in the bios called CPU FAN TARGET, which I set at 50⁰ C and a Min CPU rpm (currently at 2500).

I checked these:

The fan (ok)

Bios settings (looks ok)

 

Anyone has any idea of what's going on???

Is there a good reason for the fans's PWM signal to just drop down??

[LogicalDrm]

23 hours ago, Ark1375 said:

The fan (ok)

This would be the point of failure. How did you test it? With another fan on CPU header?

[Ark1375]

On 12/7/2020 at 12:23 AM, LogicalDrm said:

This would be the point of failure. How did you test it? With another fan on CPU header?

No, I used an arduino to generate the PWM signal and the fan works pretty much ok

[LogicalDrm]

5 hours ago, Ark1375 said:

No, I used an arduino to generate the PWM signal and the fan works pretty much ok

So you don't know if it's the fan or header doing it. Could be either failing. I don't see any other reason for this behavior. Since it has just started. Seems like power delivery issue.