the stream

Mac Mini early 2009 temperature sensor placement

Alexander Bochmann Wednesday 11 of August, 2021
I noticed that the old Mac Mini I reinstalled with Linux (a longer story involving the rEFInd Boot Manger) was running quite hot as soon as it got a bit busy. After installing and (auto-)configuring lm-sensors it turned out the fan was running at low speed despite the high temperatures.

I had at some point replaced the SSD I had in there (instead of the original SATA disk) with a different model. There's a temperature sensor glued to the front of the disk, which is a feed to the automatic fan speed management. The original disk (and the older SSD) had a metal casing, which acted as a heat transport to the sensor. The new SSD is enclosed in plastic instead, and while I put the sensor to the same position, it never measured the temperatures required to spin up the system fan.

For now, I ended up placing the sensor to the rear on top of the shielding of the Wifi module instead (the chipset heat sink didn't seem like a good idea). This seems to work well enough, and the fan now actually turns up when required:

$ sensors
Adapter: ISA adapter
Master :     2424 RPM  (min = 1500 RPM, max = 5500 RPM)
TC0D:         +46.2°C  
TC0H:         +45.8°C  
TC0P:         +47.0°C  
TH0P:         +59.5°C  
TN0D:         +68.8°C  
TN0P:         +57.5°C  
TW0P:         +56.5°C  
Tm0P:        -128.0°C  

Adapter: PCI adapter
temp1:        +68.0°C  (high = +95.0°C, hyst =  +3.0°C)
                       (crit = +100.0°C, hyst =  +2.0°C)
                       (emerg = +135.0°C, hyst =  +5.0°C)

Adapter: ISA adapter
Core 0:       +44.0°C  (high = +105.0°C, crit = +105.0°C)
Core 1:       +46.0°C  (high = +105.0°C, crit = +105.0°C)