The solution to a random shutdown/overheating iMac G5! Fan Mod!

Discussion in 'PowerPC Macs' started by breakdown77, Aug 5, 2009.

  1. breakdown77 macrumors newbie

    Jul 29, 2009
    Before I begin, I'd like to say thank you to the people here who helped me realize it was indeed a heat problem over just a "logic board" malfunction. Who knows, maybe when G5 processors get old, they start belting out more heat. Heck, my G5 was IDLING at 80°C! That's insane!

    What's more insane is how useless my once amazing iMac had become. I could no longer type term papers because it would overheat and the automatic shutoff would kick in... bam there goes my paper.

    All that to say, I finally finished my fan mod on my iMac. It was almost painful to watch my Dremel slice through the clear plastic casing and shred trough the aluminum heat spreader... but it had to be done! Now my gorgeous iMac has some sweet cool blue LED fans on the back that won't let her climb above 50°C! Thats a 30°C drop from my IDLE temp! And thats with me doing several tasks at once. G5 my friend, you have been reborn!

    It would only be fair to disclose how I did this type of surgery, seeing as there is a lack of detailed steps on the internet. So here it is, enjoy!

    Step 1: Head to Radio Shack and buy the following:
    a) 12v DC power supply ($20) b) 2x Thermaltake 80mm blue LED fans ($20pair)

    Step 2: Then pop over to a hardware store to get the following a) box of butt splice pieces b) a switch (if you want... I like having a switch on the back)

    Step 3: Test the fans with your DC to make sure they work (and to make sure you know how to wire it all together)... basically, combine the positives from both fans and the negatives from both fans then run them to the DC you got via the butt splice connectors. The switch goes in on the positive wire before the fans... just being thorough.

    CAUTION CAUTION! Please be careful here! The next steps are irreversible! Only people who know what they're doing or who don't want an oversized pretty paper-weight anymore should continue!

    Note: This is a good time to remove the RAM from your iMac. You don't want to accidentally slice it while cutting through the casing on your heatsink!

    Step 4: The gruesome part! Use a cutting tool, preferably a Dremel ($55 from Lowes) to cut an opening around your G5's heatsink. To do this, its best to take out that lower fan unit altogether, which isn't very hard (lift the latch that holds it down). Cut twice, both close to the edges of the whole heat sink unit but be careful not to slice up the copper heatsink. The purpose of all this is to expose the heatsink to the fans you'll be mounting on the back of the case.

    Step 5: Yes, I'm assuming you know how to take the back off of an iMac. This is where eye skill plays a significant role. You have to determine where in relation to the heatsink to cut a gaping hole in the back of your iMac. If you're good, it will be directly over the heatsink (mine wasn't perfect, but it worked). It took me several hours using my Dremel to finally cut through the plastic (which basically melts out of the way making a mess) and aluminum on the inside of the back cover.

    Step 6: You should have an exposed heatsink, and a back cover with a gaping hole in it. Next step is to measure out holes to drill for your fan. I used the Dremel for this (stupidly) but it was incredibly hard to control and i ended up making large holes in the plastic just trying to break through the aluminum. I'd recommend clamping the case down and using a real drill with a bit that can cut through metal pretty easily.

    Step 7: Mount your fans! I only used 4 screws, due in part because I couldn't stand working with my Dremel anymore. To keep the fans together in the middle, I just zip-tied them... easy, and it works. To clean up the sharp edges on the aluminum and heat sink case, just use the sander tool that comes with the Dremel.

    Step 8: Test your fan once again! If you installed a switch with it, make sure its working. Put the case back together, make sure everything fits and is not in the way (screw ends from the fans) and close it up. Plug in your stuff as usual, and turn on the fans before you turn on your comp.

    There ya go! Hopefully your saturday isn't completely wasted, because now you have an iMac G5 that doesn't feel like quitting on you because he's dying of heat stroke! Let me know what you thought of my method and if i should have made any improvements!

    Not sure if the site allows it, but I can post some sweet pictures of my mod. The iMac truly looks sweet with blue LED fans on the back of it!
  2. breakdown77 thread starter macrumors newbie

    Jul 29, 2009
    Here are 2 pictures of my iMac's surgery:

    Exposed Heatsink

    Completed Cool Blue Fans
  3. MattZani macrumors 68030


    Apr 20, 2008
    Or, surely just completely clean the thing out, and check the original fans?

    Mod ruins the iMac, but is effective i guess.

    Picture is deceptive, thought i had missed a super slim iMac :p
  4. Theclamshell macrumors 68030

    Mar 2, 2009
  5. breakdown77 thread starter macrumors newbie

    Jul 29, 2009
    Oh no question my iMac is ruined... if you consider ruined a giant hole in the back of the case. But my beloved iMac is useable again... its great! I just played wow for like 3 hours... never got above 50 deg C! Definitely worth it. Besides, the fans cover up any blemishes.
  6. SnoopyII macrumors newbie

    Oct 24, 2009
    I did the fan mod also after exhausting many other "fixes". It is running stable.

    Reset NVRAM.

    cleared the preference file.

    reset the SMU.

    cleaned the fans.

    checked for bad caps on board and PSU.

    removed the mainboard and reapplied thermal paste to the CPU.


    Finally I broke down and did the mod.

    I installed a 120mm clear fan with metal finger guard.

    I removed the top layer of the heatsink duct (the aluminum part with te big "G5" logo)

    I dremeled the bottom layer of the heatsink duct (I cut a nice rectangular slot on the top of the bottom layer to retain some "ducting effect")

    I also cut a 1" x 1 1/2" rectangle in the side of the PSU (the side facing where the original fan was)

    Removed the original fan.

    added a 1" fan and placed it over the slot i cut in the PSU (I harvested it from a CD-RW drive that was dead.

    Made a piece of ducting that routed air from the bottom of the heatsink duct toward the PSU.

    End result> It is running @ 57 to 59c idle and under full extended load it is around 69 to 71c.


  7. rtrt macrumors 6502a

    Jan 19, 2008
    Like this update to the thread - thanks for the write up and pics. have a few q's for you;

    Can you post a pic of the 1" fan and duct and what are the benefits - finding the psu running cooler?

    Mine overheats and switches the iMac off. I'm running it outside the chassis with an extension cable - problem fixed for now.

    Where are you taking the power for the 2 fans from?

    How hot does your disc run? - mine gets up to 55C + and the fan only slowly increases at that sort of temp - needs to ramp up sooner and faster imo.
  8. SnoopyII macrumors newbie

    Oct 24, 2009
    I will post a couple of pix later tonight.

    Yes it helps cool down the PSU

    I clipped the wires from the original "Mac blow dryer" fan. There are 4 wires. black, brown, gray, and a black one with a gray stripe.

    The black and brown ones are the wires you want to use. The Black wire from your new fan goes to the black wire from the original fan and the red wire from your new fan goes to the brown wire from the original fan.

    The other two wires are for the temp diode/speed control (which is built into the original Mac fan)

    My hard drive runs at around 35 to 38c. I don't think I have seen it go up to 40c ever.

    For reference I have an iMac G5 Rev. "A"/1.6ghz CPU/17"LCD/1gb RAM/160gb HDD.

    I will also take a picture of the location where the original fan plugs into the board.

    My system fan runs at 3200 RPM's and my HDD fan turns at 2000 RPM's.

    Oh I also cut out the "cheese grater" vent on the back piece where the CPU ducting connects to the back of the iMac.
  9. rtrt macrumors 6502a

    Jan 19, 2008
    Ok right - i'd assumed the fan was in addition to the existing - can see it would be simpler and probably better for the psu loading to replace it.

    Mines a rev B 2GHz 20" ALS - base fan speeds are 1500 cpu, 1700 system and 2300 hdd.

    Unfortunately there's no way in software (that i know of) to speed them up as i think that might solve my psu and hdd overheating probs.

    Thanks for talking me thro the wire colour coding - am thinking maybe i should do a similar mod to yours but for the hdd rather than the cpu

    When you say cheese grater - is that on the bottom?
  10. SnoopyII macrumors newbie

    Oct 24, 2009

    This is my homemade rigged up ducting. The exhaust air from the bottom of the heatsink gets routed toward the mini fan that I mounted on the side of the PSU.


    This is the location of the CPU fan connector (on my G5 17" rev. "A". It may be in a different location on your model/revision) It is recommended to clip the wires near the original fan not near the fan plug on the motherboard.

    The "cheese grater"

    The ducting from the CPU heatsink presses against it and routes the exhaust air out of the slit that is a about 2 1/2" below the top of the back of the iMac.

    By removing the grating it frees up around 35% more exhaust air exit surface area.

  11. mrsir2009 macrumors 604


    Sep 17, 2009
    Melbourne, Australia
    The light on the fan makes it look real classy!
  12. Big-TDI-Guy macrumors 68030


    Jan 11, 2007
    Glad to see you solved your issue.

    I'm curious - at any point (prior to the mod) did you check to see if your heatsink was properly mated up? I've noticed more and more hi-power CPUs / GPUs decoupling from the heatsink due to grease / indium foil migration over time.

    Ditto that for the switching transistors / FETs within the PSU itself. (had that happen to me recently on a PSU actually, just needed to re-torque the heatsink mounting hardware, and smear some glyptol onto it)

    Good to see your mod did the trick regardless - just wondering if there may be a slightly less-invasive procedure for other bold DIY'ers.
  13. SnoopyII macrumors newbie

    Oct 24, 2009
    Yes. I completely removed the main logic board, inspected everything, and reapplied thermal compound (I even lapped the heatsink lightly to make sure it had a nice, smooth surface)

    I exhaustively tried many hardware and software fixes (and yes the mosfets appeared to be seated properly also)

    I only dremeled the exterior as a last resort.
  14. rtrt macrumors 6502a

    Jan 19, 2008
    Thanks for posting the additional pics snoopyII - appreciated.

    not sure mine has the cheese grater but i can see why you'd remove it - will have to check mine at the weekend.

    think there's a connector just where you show - right next to the on/off contacts - might well be the same fan.

    admit i'm a bit confused by the psu and cpu ducting - are you taking air from the psu and putting it thro the cpu heat sink or the other way around?

    it seems to say the latter but wouldnt that risk overheating the psu?
  15. SnoopyII macrumors newbie

    Oct 24, 2009
    I am routing air away FROM the CPU duct and TOWARD the PSU. The air coming out of the CPU duct is very cool air.
  16. rtrt macrumors 6502a

    Jan 19, 2008
    understood - might need to try something like that if i decide to put my psu back inside the chassis
  17. SnoopyII macrumors newbie

    Oct 24, 2009
    I got industrious and cut a vent slot in the bottom of the PSU (well technically it would be the SIDE of the PSU) but it is at the bottom when the PSU is mounted inside the iMac)

    It is functioning as an exhaust vent for the PSU fan.

    I also taped off the top of the PSU to help duct all of the air towards the exhaust vent.

    The last noticeable hot spot is now greatly reduced. I think I am done modding on it for awhile.

    This has been my first experience modding a mac (I am a PC user)

    I bought the iMac at an auction for $85.00 with the description "loud fan noise, shuts off after 40 minutes" so it was a good gamble and not a great loss if I killed the iMac during my experiment.

    Originally I thought it might be a sticky or dirty fan but after inspecting it and reading up on it I saw that it is a design flaw/hardware flaws.

    In all fairness I have done much more radical & cruel things to PC's. :eek:)
  18. rtrt macrumors 6502a

    Jan 19, 2008
    Agree with the design flaw/hardware flaws and since i paid full whack for mine back in 2005 am keen to keep it going a while longer.

    I'm going to bookmark this post and if i decide to get a bit more adventurous then i might do some of this to get the psu back in and maybe try to cool down the hdd a bit as well.
  19. SnoopyII macrumors newbie

    Oct 24, 2009
    Here is a diagram of the iMac airflow:

    Hot air coming out of the PSU top vents and going over the caps to me isn't optimal.

  20. rtrt macrumors 6502a

    Jan 19, 2008
    yep see what you mean - not seen a pic like that before - thanks for posting.

    it looks a little different to mine - might be a 17" at a guess - but everything is in the same place more or less.
  21. 300D macrumors 65816


    May 2, 2009
    The main issue is the heatsink is much too small for a G5 in the iMac. Thats why there was never a Powerbook G5.
  22. cfos macrumors newbie

    Jun 30, 2010
    How's it Workin'??

    I am considering your fan mod for my 2004 imac G5. I am curious if your system is still working one year later before try it.
    Thanks for any feedback,
  23. kbfr08 macrumors 6502

    Mar 16, 2007
    Since your imac is already ruined, how about ditching the 12v psu, and soldering the fans to a 12v+ point on the logic board. Maybe upping the cpu's multiplier as well ;)

    I can pull the schematics off of my iMac and give you a few locations for 12V pads and test points.
  24. jptjr639 macrumors newbie

    Jul 3, 2010
    great to see!

    I'm running 70c on 17" 2.0 ALS and I was trying to track this page down based on a recommendation from iFixit. I'm on my second hard drive with this thing and I don't want to go for thirds. For those who've done the Mod how's it going? I look forward to taking my Dremel out again and watching the plastic fly!
  25. breakdown77 thread starter macrumors newbie

    Jul 29, 2009

    A year or so later and my iMac 17" is still running strong. The mod was definitely worth it. One issue to consider however is the dust factor. My mod was by no means a clean one (I'm an amateur btw) so dust is frequently a problem. Every month or so I have to pop off the back cover and give it a good pressurized blast from an air can.

    Other than that, go for the mod! If your iMac is running how mine was, then an alternate cooling system is definitely worth it.

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