Imac 20 inch early 2008 randomly switches off

Discussion in 'iMac' started by MacDoogal, Oct 3, 2014.

  1. MacDoogal macrumors newbie

    Oct 3, 2014

    First post on this forum so sorry if this had been asked/answered elsewhere.
    My sister in law has an early 2008 20 inch iMac which has given good service for the last few years, however recently (last 6months or so it has developed a habit of randomly just swathing itself off. She then restarts via the power button and all is OK until next time. This may happen2-3 times during the time she writes on shortish email.
    She has tried disconnecting the printer (originally we thought it happened when printing!) but the problem still exists. There is very very little on the hard drive and the machine is still running the original OS it came with. When it is running it is great fast to boot and load programs etc. The mac is only used for Web surfing and mail.
    It has been to the local Apple Store who say they can't find anything wrong and in any case she ought to be thinking about a new machine as hers is well out of date for repairs or parts etc!
    I wondered if there were any things one could look at or if anyone else had experienced this?

  2. Brian33 macrumors 6502a

    Apr 30, 2008
    USA (Virginia)
    Hi. I've got an Early 2008 iMac, but it's the 24" version. My guess (and it is a guess, but hopefully an educated guess) is that the machine is overheating and shutting itself off to prevent damage. This could occur after years of dust accumulation in the CPU or GPU heatsinks. If this is indeed the problem it is fixable.

    There are a number of applications available that will report the values of the various internal temperature sensors and the current cooling fan speeds. I happen to use iStat Menus which is a paid app, but I believe there are a bunch of free apps also. You could try one and monitor the temps/fan speeds to correlate with the unexpected shutdowns, and also report them here to try to see if they're typical.

    Someone who is methodical, patient, and reasonably handy with tools can open these iMacs and clean them out (I have) and apply new thermal paste if indicated. I found the guides at to be invaluable for my machine.

    I agree that these machines are still very useful and I encourage you to find a solution if it otherwise meets her needs. Mine is still my "daily driver" and I do a fair bit more than web surfing and email! (Although I have increased the RAM and installed an SSD.)
  3. MacDoogal thread starter macrumors newbie

    Oct 3, 2014
    Hi Brian,
    Sorry for the delay and thanks for your reply.
    I have not had the opportunity to question my sister in law more closely and have a few more details which may help to shed some light on the problem...

    The problem seems to be connected with the printer. Whenshe hits the "print" button in Pages or Email the iMac will switch off. Then machine will then reboot and printing can be done OK. This can happen a fews times in a row.
    Sometimes if the iMac has been on for a while it will switch off spontaneously. There is then a "whooshing sound" which I suppose is from the fan(s). The machine then has to be unplugged from the power wall socket before it will reboot. (pressing the power button on the iMac makes no difference).
    In the hope of solving the problem she has removed the printer - problem the same. And also replaced it with a new one, when she put the disk in to do the install the iMac again shut down!

    I did read about PRAM resetting, is this a possibility?
    Best regards,

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