iMac Intel 27". EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz), EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz)

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Third Hard Drive Connection Cable (Heat Sensor?)

When I removed my original hard drive from my 2009 27" iMac, there was a third connection to the right of the two thermal sensors. It's a small four prong connector. The installation guide doesn't mention it and the new hard drive I got to replace the original one doesn't have an applicable slot to hook this third connection up.

I'm currently stuck with an iMac that's pulled apart and no way to know if this connection point is necessary or how to proceed.

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What are the last three digits of your serial number?

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iMac "Core i5" 2.66 27-Inch (Late 2009) 2.66 GHz Core i5 (I5-750)

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This model has an internal hard drive temperature sensor.

Are you talking about the connections on the drive? Review Step 10 of this guide HD Replacement

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Dan,

After doing some reading last night I found out about the proprietary temperature sensor on the hard drives for the iMac of that model. This is what I think it is. It's not either of the two main connections on the drive.

I read about a possible solution of installing the new drive and running http://exirion.net/ssdfanctrl/

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Well sorta yes, I would return the drive and get one of the drives that now support the internal sensor. You should get the same vendor's HD of the series your older dive is (larger size if that is what you want).

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Turns out it's a proprietary port that Seagate uses for their warranty and testing purposes. Apparently Apple used it to lock up a temperature gauge to it.

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Sorta yes here as well. The SMART standard call out for these pins for thermal sensor. But as always the definition of how it's used was never properly defined (everyone did their own thing). I'm sure Seagate as well as the other HD vendors used it as a test point {also note: not all drives have this sensor}. But Apple wanted to use it for system heat control. So they worked with the vendors on how they wanted to do things and they complied. The rub here is Apple used all of the drives they could so it took awhile for the open market to get these drives (remember the floods in Thailand cut HD production).

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I replaced my defective Seagate hard drive on my iMac with a SSD.

Considering the poor reliability of Seagate drives and the substantial improvement with SSDs, I would never consider putting in another Seagate because of the internal sensor.

The link (from Dan) to exirion,net for a program to control the fans worked perfectly and was the best solution in my case.

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Sorry to here you had a though time with a Seagate HD. I promise you all of the HD vendors are basically the same here in reliability. True, Seagate has had a bad run of drives a few times (as well as the others). For some reason Seagate got bashed more in the news. I have a closet littered with Hitachi, Seagate, Toshiba & Wester Digital drives equally.

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As to using some form of fan control app from experience I can tell you over the long haul its not good for your system. Many of these use a fixed setting so if you have more heat they don't ramp yup the fans to cool the system. The other direction of over running the fans shortens the life of the fan units and adds more dust internally. So I do strongly recommend not to use them. Instead I do recommend adding a replacement sensor (for SSD replacements like in your case). Here the a spare optical drive sensor is used to replace the missing sensor in your SSD unit. Then the system is happy and the SMC services can ramp up or down the fans as needed.

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One last point: At the time I wrote this we didn't have many options. Today we do with better drives. The floods in Thailand had a silver lining! Many of the factories where rebuilt with much better automation and robots! So the quality of drives have gone way up and the costs have come way down! Today we use SSHD's in our older iMac & MacBook Pro systems internally. We have over 200 MacBook Pro systems now in the field with Seagate SSHD's. While we still get a few killed systems all can be attributed to user action not HD defect. as for the iMacs we use both HGST & Seagate drives.

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