If you’ve ever tried installing a new hard drive in one of these machines then you’ve probably already found it goes something like this. Step 1. Spend an age delicately removing that big ass glass panel and then screen, installing the new drive, putting it all back together (careful, no dust). Step 2. Coming to the stark realisation the hard drive fan is spinning like a mad man and your quiet and serene iMac has turned into something of a 90′s gaming PC. Time to take it all back apart again then.

The reasoning behind this oddity is the fact Apple started using the built in temperature sensor (that most hard drives contain) to monitor and adjust the fan speed accordingly. Now you may think, ok so if I replace the drive with the same make and model Apple used at the time then all will be ok? Wrong. I found out the hard way by buying an exact replica of the 2TB Seagate ST32000542AS drive Apple shipped as an upgrade option back in 2009. After installing this I still got the noisy fan syndrome, and this was because unless the drive is flashed with Apple’s custom firmware then the pins used for the temp sensor cable are infact pumping out hard drive rpm signals.

Is there any way around this? There must be something we can do!!? Well yes, there is. It’s a simple mod that will get your capacities up without that dreaded fan following suit.

1. I will assume you already know how to get into your iMac. You need a couple of suction cups to remove the glass panel without cracking it. The panel is held on by magnets around the perimeter of the machine. For a detailed guide in opening her up, then check this. NOTE: Unplug the power cord!

2. Once inside and the screen is removed (careful with the screen cables, especially the one in the top left!!) you will have access to everything and the hard drive is slap bang in the middle.

3. Here’s the clever part. We need to replace the current temp sensor cable going to the hard drive with an external temp sensor. Now there’s another drive in your iMac that is constantly getting monitored, and that’s your Optical drive. That uses an external temp sensor with the exact same plug on the end as the hard drive cable. Put two and two together and you realise we can buy a spare Optical drive sensor and stick it on the hard drive. Bingo.

4. The part number you need is 922-9229, I got mine from TheBookYard here in the UK. Google the part number and you should find a supplier in your locale. Check the picture above to see where I installed mine. It’s been working flawlessly for about a month now.

If you have any questions then use the contact page to get in touch.

I recently bought myself a brand new Samsung 750GB SATA hard drive to put in my ‘Late 2006′ 20″ iMac. The machine is a 2.33GHz Core 2 Duo with 2GB RAM and a Radeon X1600 Pro 256MB. So I followed the steps to open it up and removed the screen, then replaced the drive and reassembled.

Next I booted up and everything seemed to be fine, started installing Leopard and noticed it was taking a while to install, 5 hours to be precise! I then put my old hard drive in a FireWire Caddy and used Apple’s ‘transfer data from another Mac’ option to get all my files back, this took about 16 hours!

After all was done I started using Leopard for a while only to find that every minute or so the system would beachball and become unusable for about 2-3 minutes. It would then catch up with itself and a minute or so later, beachball again! I trawled the internet for answers and found someone else on the Apple Support forums that had bought the same hard drive and had exactly the same issues. He told he’d returned his Samsung drive and bought a Seagate model, which he said worked fine.

Two days later I have my new Seagate 750GB hard drive waiting to be fitted. I go through all the motions again, removing the iMac’s front, taking out the screen, installing the hard drive. Guess what, it also had the beachball problem! I even tried using a jumper setting to force SATA 1.5Gb/s mode, still the same!

So now I’m back with my original Seagate 250GB hard drive installed, and am booting the iMac from the Samsung drive using my FireWire Caddy! No beachballs at all now! I can only think that the SATA Controller in the iMac just can’t cope with a drive bigger than 500GB. Time for an Aluminum iMac I think…