iMac Intel 27". EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz), EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz)

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CPU Fan runs at full speed.

Hi, the CPU fan of my iMac is running at full speed. iStat says it's not running (0rpm). The temperatur sensor is working, my ASP says, that's a problem with the logicboard. Any resets (SMC, PRAM) are done but this problem is still there. I just bought an external fan control but first I want to ask if somebody know the pin assignment of the CPU fan plug.

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Has the hard drive ever been replaced?

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Nope only the fan has been replaced.

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Something is not right here with iStat. Do you have the older widget or are you use the current version? Give Temperature Gauge a try, does it show the samething? Lets see what the second tool tells us.

The fan speed sensor is part of the fan unit so you may need to replace it. I don't see the logic board as the issue here, pending what new info you can tell us.

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Well I tried smcFanControl like this guy here: CPU fan runs full speed

But with no success. This tool shows me 0rpm too, I installed the SSD Fan Control tool to have a look if the temperature changes when I turn up the HDD/Optival fan. Yes it does even the CPU Temperature is changing a bit.

The device was at a ASP last week because the graphics card was broken. They tested the device, found a broken HDD fan they renewed it an then, they say that the CPU fan is broken too, so they tried it with several fans with no success, so they guess its a problem with the LogicBoard.

Now I get this code from AHT: 4MOT/4/40000002:CPU-0, but I can hear it running, and the Temps are okay too (in °C)

https://dl.dropboxusercontent.com/u/4619...

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Well another program shows me that the internal HD is at 0.0°C

https://dl.dropboxusercontent.com/u/4619...

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Here is a handy article on how to decode Apple error codes CNET - How to invoke and interpret the Apple hardware tests

So looking at your AHT error: 4MOT/4/40000002:CPU-0

4MOT- Fan motor

CPU - Of course is the CPU

What is odd here is the error 0 I've always seen some three or four digit error here we see none.

Then we have FanControl showing 0 temp on the HD. I'm wondering if the SMC needs a reset here.

But, before we do that can you tell me how you have the system powered are you using a UPS or a surge suppressor (not a power strip) and have you checked your household power services to make sure Ground is good and you have no power fluctuations. Do you get a lot of lightning storms in your area? If you do have you noted the light flickering or have had power outages?

If any of this holds true you may need to replace your surge suppressor (damaged), repair your power services and/or talk with your power supplier. If you have a UPS you may need to replace the battery or it may not be able to support your system through a power disruption.

Here's a good Apple TN on resetting the SMC Intel-based Macs: Resetting the System Management Controller (SMC) as you can see one of the symptoms of a messed up SMC is the fans running high in the TN.

Lets also check your SMC firmware level and if needed update it. Follow this Apple TN EFI & SMC firmware updates for Intel-based Macs.

Let me know what you discover.

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Well I did the SMC Reset, pluged the Mac to another plugbox and I'm not using a UPS or surge suppressor. The power services are good too, ground tested and no fluctuations.

Well I don't know if the reset is done properly, I'm not standing there with a stopwatch. But normally I disconnect my Mac when it's shutted down. So a SMC reset is done all night.

I tried to install the firmware updates but it is said, that they are already installed.

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Are you still getting the AHT error when you run it? Is the fan still running at full tilt?

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I had done the same thing when dismantling the iMac 27" Mid 2010 Model, the internal heat sinks where clogged with dust making the iMac run really hot (but strangely all the FANS remained at normal speeds), so as I have done countless times with notebooks I dismantled the unit and removed the main logic board, but in my dismantling when i pulled out the power button cable connector, i must have inadvertently ripped off the SMC resister just above the connector there and this made the CPU FAN report 0rpm which causes the system to run the CPU FAN at maximum speed, I do not know what the correct resistor was but i tested the resister directly above it and it reported as 10k ohm, so i took a guess and soldered on a new SMC 10K Resistor and prayed it would work :) lucky enough it did and now the CPU fan is reporting 950rpm at idle. So I hope this helps, but if anyone knows if the resistor marked (R5797 on the logic board) is 10K or not, I would like to know :)

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Wow! This really helped! I'm using my 27" iMac for school as I study graphic design.

But since a month or so my cpu fan blows at full speed. (I had to take out my logic board to repair a broken internal display connector)

I've done so much this past month: took it to Apples technical service, replaced the fan, took it again to technical service and finally got the news that my logic board had to be replaced for a rough 600 euros (Belgium).

Your post made me search to that resistor and indeed the one you're talking about is broken off.

Could you give me more detail about the replacement part/resistor you used? :)

Thanks!

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The resistor I used was a 10K ohm surface mount type (I didnt have the original resistor to test so i tested the resistor above the one that was missing and it read 10k with my multimeter, so i took a educated guess the missing one was also 10k) I then salvaged from some old electronics boards a 10k ohm SMD type resistor that was slightly larger than the original one, but it is so small and tiny you need tweezers and a 0.5mm soldering iron tip and a magnifying glass with light and a very stable hand to solder it back. But after I successfully soldered it back in place, the iMac went back to normal fan speeds :) I hope this helps :)

Resistor is like this one:

http://au.rs-online.com/web/p/surface-mo...

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I have one of these iMacs and, following your advice, I looked for the resistor and found that I too have a missing one right next to the power button connector. I touched one of those color banded 10kohm resistors to the contacts and immediately got an RPM reading for the CPU fan. The fans turned right down and the computer seemed much happier.

Next step is to have someone more skilled than me place a resistor on the board but this is definitely the culprit.

I took a couple pictures so anyone else with this issue can pin it down. FWIW, the spot was fairly easy to find once I knew it was near the power button connector. Only had to remove the glass, display, and power button cable to find it.

From afar: http://i.imgur.com/8W8SpxR.jpg

Close-up: http://i.imgur.com/hbvNIE3.jpg

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Okay so the actual resistor for that is a 47K 1/16W 5% in a 0402 package.It's around $0.10 at places like digikey.com etc. It does control the Fan Tach circuit

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Cool! How'd you figure that out?

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Did you fix that problem?

Update

Fixed my iMac: broken resistor right next to Pwr button connector.

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Can you give us some more info on this resistor (picture please) and how you figured it out.

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Would be great to know!

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Okay so the actual resistor for that is a 47K 1/16W 5% in a 0402 package.It's around $0.10 at places like digikey.com etc. It does control the Fan Tach circuit

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I can confirm that the fix works.

Got help at my office to mount a "47K 1/16W 5% in a 0402 package" at the place specified in this page.

They said at my office it looked like there where something mounted there before but is now missing.

After mounting the resistor the fan speed return to normal.

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Well I tried several things, my solution is not the best but it works well. I bought an external power supply 3V to 12V and a potentiometer and build a controlunit for the fan. Then I installed Macs Fan Control and this program turns on the other fans if the CPU is going over 80°C and then I have to run the power supply at 9V ;)

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Update on my situation: Ordered the correct resistor based upon this diagram http://lkcomputers.com/janhoffmann/Apple... a "47K 1/16W 5% in a 0402 package."

Had a friend solder the little guy onto the board right above the power button connector and it totally solved the problem. Looks like it's really easy to break that resistor off while plugging that cable back in. Probably pretty impossible to even realize it happened because of the size.

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I too accidentally took the small resistor out while trying to upgrade my CPU and the cpu fan run at full throttle.

By the way where did you order the resistor?

I'm so glad i came across this discussion as it is very useful.

Peace!. :)

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Just like to add:

You can order the resistor at digi-key

partnumber: RMCF0402JT47K0CT-ND

http://www.digikey.ca/product-detail/en/...

it cost me $6 total.

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Well I opened the MAC and put an external power supply unit to the fan with a poti in between. I let it run an 7V and got the poti in a mode it is very silent. If the device is getting too hot, I put the PSU at 9V.

I also installed MACS Fan Control and say, that it should turn on the HDD Cooler if the CPU temperatur is going over 75°C, so I was informed to put on 9V mode :D

Well it's not the best solution but an new MAC is not far away .

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Could somebody tell me how to connected the three wire of a Zalman Fan Mate 2 potentiometer with the four wire of the fan?

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You have to try it, there are 3 black cables one is - one is 5+ and one is 12+ the best way is to use the external PSU to find out which is the right one and then mark it. I used the Trial and error.

PSU --> Zalman black and red zalman Input --> CPU fan. Maybe you have to split that Input to the yellow/White one to make the fan move.

But my Fan Mate is getting very hot after a while and now I ise something like this: http://amzn.to/1KPdq6J

PSU @7.5V and fine adjustment with the potentiometer.

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Thank you for your reply, I will try. I am waiting delivery of my Zalman Fan Mate 2.

For what is your alternative, this product is not available in Canada. I'm looking for an equivalent.

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Well it's something like this: http://bit.ly/1QT89ia maybe you will find something similar in canada.

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I finally installed the Zalman Fan Mate 2. It works very well for minimum and maximum speeds. The intermediate speeds are more difficult to adjust. The whole is very satisfying and I have not seen yet exaggerated heat.

I could find in Canada a similar potentiometer to the one you suggested, but I thought 4W was not enough and I was looking for 6W minimum.

Thank you again.

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Good luck with that!

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If rpm=0 then control the fan connector , could be a fake contact of the rotation sensor , slightly pulls the wire into the connector , I have solved this way the problem

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I had done this once, i pulled the wires out the fan plug by mistake, and put them back in the wrong way so the fan span out of control. However i followed the wires round with my thumb from top of fan and managed to get them in the right order. Fan was as quiet as a mouse after that. Don't know if that is your problem but so easy done.

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Anybody know what the value of L5701 is? I accidentally ripped the %#*@ pad of the side that goes towards R5797...currently testing (jumping) with kynar and a couple resistors. Thanks.

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Just in case someone else encounters this apple hassle, L5701 has no value...added a 0 ohm resistor from another junked PC board, jumped it with kynar to the corresponding spots (because of ripped pad) and fixed the issue.

You need a steady hand, magnifying glasses, fine tip, voltmeter, experience with tiny resistors and a friend with mac to know where is and not continuity on those resistors in order to accomplish this type of repair. Good luck!

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