Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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Where is my secondary Heatsink?

Hey there,

can anyone please tell me, where i can physically find the "Power Secondary Heatsink" Temp Sensor ?

iStat Pro tells me that the Temp sometimes runs up to 90°Celsius (approx 194°F) (with a CPU Load up to 60% )

IDLE the 2nd Heatsink is about 60°C - 75°C (140°F - 165°F)

'''Today i disassembled the iMac completely and i looked for all those Temp. Sensors, but i couldn`t find anyone on a "Heatsink" only near the CPU & the GPU, Ambient, Display, ODD,.

is it maybe on the Power Adaptor?


1,5 Years ago, i upgraded a SSD -CORSAIR Force 3 and to Control the HDD Fan i use SSD-Fan Control,

(it runs Manually 1700Rpm, cause the S.M.A.R.T. stat from the SSD couldn`t be read out by the iMac... don`t know why, maybe a Firmware Bug)

thx for your help!

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I do believe the power supply has a thermo sensor on one of the heat sinks. As far as a firmware bug, no, I suspect you didn't properly connect the HD thermo sensor. Did you not remove it from the HD when you swapped it for the SSD? So it could be mounted onto the SSD.


Hello Dan,

no the ThermoSensor HDD is just a Cable with a Connector which is plugged in to the Original Apple Seagate HDD, and plugged in to the Logic-Board.

The Corsair SSD has not the Specific Firmware to Send TempInformations to the SMC. either not the Connector-Input to plug in the Cable.

The Temp Sensor for the HDD is not one like the Temp Sensor ODD or the other ones (Electrician would say: it`s not a NTC (negative temperature Coefficient or PTC (positive temperature Coefficient). Its only a Connection between HDD Firmware and Logic Board.


Apple is consistent with their temp sensor's all of them as far as I've seen are a diode type. How it is used within the circuitry of the system (NTC (negative temperature coefficient or PTC (positive temperature coefficient), is really not needed to be known on the most part (unless you are trying to reverse engineer things here).


yeah, you`re maybe right, don't know... anyway... next time, i disassemble the iMac i will take a look at the Power Adaptor, maybe there is a Temp Diode ;)


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I'm confused here Shane - Did you still have your HD still installed in the system? I thought you swapped it out with a SSD. If you did the sensor is internal to the HD Internal sensor.

You could get an external HD sensor or short the cable out (telling your system the HD is always HOT). I prefer getting a replacement sensor than using software to override the fan's.

But this is not the sensor I was speaking about in my comment.

Apple has a lot of sensors in their systems. In my '11 iMac I have four sensors just in my power supply two on heat sinks! We don't have any more 21.5" models so I can't tell you how many you have and your description on what you were looking for was a little vague.

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Hello Dan,

i replaced the Original Apple HD with a SSD from Corsair, i left the HD Sensor Cable out (Its not Connected anymore, neither on the Harddisk, neither on the Logic Board---> its in the Drawer in a Cupboard) i control the HD Fan with the small APP "SSD-Fan Control" --> it works Fine.

I Check out, which Fan i have to speed up to cooling this Secondary Heatsink.. the Only Fan which gives me a cooling Effect for the Secondary Heatsink , is speed up the CPU Fan, ergo, the Second Heatsink have to be Placed on the Left side in my iMac.

Here are a Screenshot with the Temp Sensor overview (iStat Pro) on my iMac 21,5 (mid 2010)

there you can see the Temps, and the Fan Speed, i Speed up the CPU and HDD Fan up to around 1700rpm (it`s quiet , and will give me an acceptable Temp inside the iMac).


iThink the whole cooling in my iMac is Okay, --> excluding the Secondary Heatsink.... thats the Only Problem i have.

thx dan for your previous Help until yet.

(maybe my English is the Reason , that reads vague for you!?


greets from Germany*


Yes, the secondary heat sink is one of the power supply heat sinks.


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