8 Replies Latest reply: May 28, 2012 5:34 AM by WZZZ
Iain MacDonald1 Level 2 (405 points)

My iMac is a 2010 model, and has recently developed some of those weird greyish marks on the screen. The kind of come and go, but always in the same place. Usually a bit wavey, but sometimes straight. Its not ideal, but its not the end of the world so long as it doesn't get much worse, and is made up of dust / particles rather than the screen actually crack and become unusable.


Anyway, I figure the most likely culprit is heat, so I've installed smcFanControl. According to the that, the iMac typically runs at between 50-55 degrees, with the HDD at around 1200rpm and the CPU at around 940rpm.


Are those remotely typical or does that sound too hot? I'm slightly concerned about the fan, as although its set in the preferences to kick in if the HDD gets to 1100rpm, it doesn't seem to come on. I assume its not so quiet I wouldn't hear it?


Is there a way ti turn the fan on manually to test it?


Thanks for any advice.

iMac, Mac OS X (10.7.4)
  • WZZZ Level 6 (12,875 points)

    What runs at 50-55 degrees? There are various temp sensors all over the Mac.


    There are three fans.


    Scroll through these two threads for my posts on using smcFan. You need to establish pre-sets. Sounds like your fans are running at the default speeds.

  • WZZZ Level 6 (12,875 points)

    Here are those links,






    And here's a huge thread, "Greyish Smudge marks behind the glass screen." Don't know if that's your problem



  • Iain MacDonald1 Level 2 (405 points)

    Thanks for the links. I did see the long thread about the marks, but I was interested mainly in the heat issue initially. The 50-55 degrees is in reference to what smcFanControl says. I don't know which it is in reference to.


    I've downloaded the Temperature Monitor, which gives these results:


    Ambient Air - 26

    CPU A Heatsink - 53

    Display screen proximity - 51

    Graphics Processor Heatsink 1 - 64

    Graphics Processor Temperature Diode - 65

    Main Logic Board - 56

    Optical Drive - 51

    Power Supply Position 2 - 68

    Primary Heatsink - 66

    SMART Disk - 54

  • WZZZ Level 6 (12,875 points)

    The SMART Disk is the drive. 54 is on the hot side. I  like to see the drive to stay in the neighborhood of 45-48. Of course, depending on the ambient temp, lower is better. The Power Supply at 68 is also high.


    In addition to usng smcFan, I run a small clip-on fan at the back of the computer. This helps dissipate the case heat.




    Here's my setup using a $10 clip-on fan mounted to a bracket on the wall behind the computer, to avoid vibration. The fan blades are about 6" from the back, and the fan is aimed at the the upper left, in particular, but covers most of the area of the back. I turn it off and on using a power cord inline switch to avoid wearing out the cheap switch on the fan itself. Even in summer, while the back may get warm, it never gets really hot to the touch.


    I periodically open the fan up, clean the blades and lubricate the front and rear shafts with a light oil.

  • Iain MacDonald1 Level 2 (405 points)

    Thanks - from reading those links I'm going to have to fess up to not doing anything with that vent above the power cord. I've given that a quick vacuum, and also switched on a fan similar to yours that we had in the house - its to the side rather than directly behind. (Not sure there's room.)


    Anyway, since powering back up for 10 mins or so (it was only off for a few minutes), the figures have dropped a bit:


    Ambient Air - 22

    CPU A Heatsink - 44

    Display screen proximity - 45

    Graphics Processor Heatsink 1 - 48

    Graphics Processor Temperature Diode - 48

    Main Logic Board - 46

    Optical Drive - 44

    Power Supply Position 2 - 60

    Primary Heatsink - 59

    SMART Disk - 45


    Do they sound a bit more like it? If so I'll keep an eye on them and hopefully they won't creep up to much. Weather sise this is about as hot as it gets here in the UK.


    Out of interest, with the marks, to save me trawling through that thread, do you happen to know if it is most likely just dirt stuck behind the glass, or if its likely to be any structural damage?


    Thanks for taking the time to post.

  • WZZZ Level 6 (12,875 points)

    Those look better, especially the drive. But still don't like the PS at 60, especially since Position 2 means it's not a direct internal reading. Right now, after running for a few hours with the room temp at around 26/78, mine is only 44.


    Out of interest, with the marks, to save me trawling through that thread, do you happen to know if it is most likely just dirt stuck behind the glass, or if its likely to be any structural damage?

    Sorry, don't know much about that. I've never been able to scroll through that entire thread. I think some are saying it's behind the LCD, not between the LCD and the removable screen.

  • Iain MacDonald1 Level 2 (405 points)

    They seem to still be falling..


    Ambient Air - 21

    CPU A Heatsink - 42

    Display screen proximity - 42

    Graphics Processor Heatsink 1 - 46

    Graphics Processor Temperature Diode - 46

    Main Logic Board - 44

    Optical Drive - 41

    Power Supply Position 2 - 57

    Primary Heatsink - 56

    SMART Disk - 42


    Where is the PS reading from? Where the power cord is attached?


    Just realised I'd missed some readings...


    Secondary Heatsink - 62

    CPU core 1 - 48

    CPU core 3 - 42

    CPU core 5 - 45

    CPU core 7 - 41

    CPU core 8 - 44

  • WZZZ Level 6 (12,875 points)

    Where is the PS reading from? Where the power cord is attached?

    Don't know exactly. Just know that Position 2, as opposed to Position 1, is not at the core. Keep the fan running at the back. That will definitely help for the PS temp. Also be sure to keep the lower intake grille and the one behind the stand dust free. The fan and ramping up the temps with smcFan -- use it conservatively at the minimum necessary to keep thngs under control -- will create more dust. Periodic vacuuming is a good idea. Have to run out for a bit now.