Chosen Solution
I have a 2009 iMac Core i7 2.8 GHz upgraded with an SSD in place of the optical drive and 32 GB of RAM. All that works great, however I have had the Seagate 1 TB drive that came with the iMac replaced under Apple’s extended replacement program. This second Seagate drive has also failed, and surprisingly I’m eligible for another free HDD replacement (even almost 4 years later). Of course I do not want another small 1 TB Seagate HDD (that may fail again) installed, and be without my iMac for a couple of days. Instead I have already installed a Western Digital Black 4TB HDD. I have read many discussions and possible solutions to switching brands because of the different connectors for the temperature connector. But I couldn’t find anyone that suggests or confirms that I can just buy the appropriate cable for the different brand HDD. I found this on eBay: Temp Sensor Hard Drive Cable 922-9225 Is there any reason I can’t simply replace the Seagate temperature cable with the Western Digital temperature cable? Are the internal sensors in the different brand HDDs actually different therefore the SMC won’t recognize the signal and adjust the fan speed appropriately? (This would suggest that firmware or the logic boards are different for each brand of HDD, I find that doubtful.) Simply replacing this cable seems like the perfect and simple solution because it has the correct connector to the hard drive. (If buying the correct cable won’t work, then what is the best software fan control solution?)
Your correct all you need to do is swap out the cable harness with the correct cable for your new HD (Seagate for Western Digital). But before doing that why don’t you get your system to Apple to get the HD anyways. Then take it out and put it into a case to use as a backup drive or even sell it. Free is good ;-} Here’s the rundown of the different temp cables: 922-9223 - Hitachi922-9224 - Seagate922-9225 - Western Digital
Using the external cable is unlikely to work correctly on a non- iMac specific drive, and it even has to be for the correct series iMac. The generic drives usually do not have the correct firmware to use Apple’s temp cable. In the case of WD drives, the late 2009 iMac repurposes pin #5 on the jumper block for temp data. On a generic WD drive, pin #5 floats at about 2.5 v. If it is shorted to pin #6, (ground, 0 v) the drive is set for SATA 150 mode. On a WD Blue drive pulled from a late 2009 iMac, pin #5 floats at 2.5v, and carries a 2-pulse signal every 4 seconds. Presumably, this either carries the temperature data, or is some kind of handshake. An Apple-branded WD drive pulled from a 2007 iMac lacks this signal, as do the new generic WD drives I tested. Apple’s 2-wire cable connects pins #5 (signal) and #6 (ground) to the logic board. If the cable is jumpered, the logic board goes to low fan. If open, or if the correct signal is not present, it goes to high fan. So, if you attach the WD temp cable upside down, as suggested elsewhere, you disable fan control and set the drive for SATA 150 mode! Fortunately, OWC offers an external temperature sensor that mimics the correct signals from the iMac-specific drive. This allows use of non-Apple drives, including SSDs in the main drive bay. It’s possible that an Apple optical drive temp sensor, which is taped in place, could work, as they do have the same logic board connector. It does not appear to be a simple thermistor. I have not checked the function of this. Perhaps someone could hook a scope up to one in a working system and see. The part number for a 2009 iMac optical drive temp sensor is: 593-1152 Why would Apple do such a thing? It’s better, and cheaper too, from their point of view. The drive’s internal sensor is more accurate than the older taped-on sensor, and not using the data stream to read temp data prevents slowing down the system. Serviceability and upgradeability with non-Apple parts has never been a top priority for Apple, as the machines are meant to be repaired by Apple and replaced when obsolete.
