OS X Mavericks Hardware Diagnostics
 

I've got a mid-2010 27" iMac 2.8 GHz Intel Core i5. The fan goes nuts after about an hour and it seems I need to run hardware diagnostics. Booting with d pressed doesn't work and if I get the Hardware Diagnostics running from the Internet it says it doesn't work with my iMac.

I am running 10.9.2 and have the Snow Leopard disks. Can I use these for hardware diagnostics? Or what else can I do?

Thanks.

I guess you've read this?
OS X Mountain Lion: Use Apple Diagnostics or Apple Hardware Test

For most(?) alternate startups, you hold the special key down immediately after the gong sound (not before or during), and until you see that it is starting differently. (my current Mac is a headless mini, so I don't do this test)

Thanks, yeah, tried that and it just boots as normal. Hmm, am I missing something?

Sounds like your keyboard isn't responding correctly. Do you have another (USB) keyboard to try?

Just tried it with a USB and still the same.

Try running the Apple Hardware Test with your Snow Leopard DVD set. You should be able to run the AHT from disk 2. Here's an excerpt from the Apple KB:

Using Apple Hardware Test on computers with OS X 10.5.5 to 10.6.8

AHT is located on the Applications Install Disc 2 and should be included with your computer or the MacBook Air Software Reinstall Drive on a MacBook Air (Late 2010). To start AHT on these computers make sure the Applications Install Disc 2 is inserted into the built-in optical drive, external Apple Superdrive, or for the MacBook Air (Late 2010) be sure the MacBook Air Software Reinstall Drive is inserted into a USB port. Please then follow steps 1-6 outlined in the "Using Apple Hardware Test on computers with OS X 10.7 or later" section of this article.

That worked, thanks!

It came up with an error that a took a photo of. Then when I rebooted a progress bar came up and it took about 15 mins to boot. What's going on in that time?

Maybe a bit of a stupid question but did you remove the DVD?

You could try installing Temperature Monitor. This makes checking the internal components temps easy. This way you could find what is over heating. Here's a link to the web site

Temperature Monitor: Description

Well, I did the hardware test from the Snow Leopard disk and it came up with a fan error on the hard disk. I restarted and a progress bar came up and it took about 15 mins to boot. I then did a PRAM reset and now I've been using it for four hours and it is totally silent! No fan overuse (it normally comes on about an hour after use)

Does the hardware test actually fix anything? Could it have been the PRAM that caused the error? Or should I be worried about imminent failure of the fan?

Normally, a SMC reset will fix a runaway fan due to management errors (SMC) but sometimes a PRAM reset will accomplish the same thing. Looks like you may have solved it with the PRAM reset. Keep your eye on it for any future problem and don't forget to make backups. ;)

Thanks, I did SMC reset initially but it made no difference. As and when I get time I'll run the hardware test and see if it still reports a problem. I did read on the Apple forum that the fan sensor can simply report the wrong information which causes it to overrun and that it can be fixed by software only so maybe that's it!

Can anyone answer my question as to why there's a slow boot and progress bar immediately after a hardware test?

Thanks a lot.

I don't really know. (I suspect something gets reset.) It does the same thing after a firmware update and can be scary since it looks like it's going to crash. However, after it initially boots the first time, everything seems to go back to normal.

It works anyway. Thanks everyone, lots of great support and help here.