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Old Jan 20, 2013, 08:27 PM   #1
Jarek104
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Problem after CPU upgrade in mid 2010 iMac

Hello everyone. Yesterday me and my friend replaced the CPU (2.8 i5 with compatible 2.93 i7) in my mid 2010 iMac using this tutorial:http://www.hardmac.com/articles/335/page1 . Everything works fine. iStat reports cpu temp of 35, HD= 41, optical drive= 31 and ambient=16. optical drive fan is 1000rpm, HD fan is at 1200 rpm but for some reason the CPU fan shows 0rpm while working like crazy. I spent the whole day looking for the answer on different forums, reset the SMC and PRAM, took the iMac apart again to check all the connections and even took it to apple store. Unfortunately I was told that they won't help me since I upgraded the CPU. The hardware test they ran showed indeed 0rpm for CPU fan but that's all the info i got from them. I also read somewhere that I could install resistor to slow down the fan but I have no idea which resistor to use and on which wires it should be installed. ANY help would be appreciated.
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Old Jan 20, 2013, 10:38 PM   #2
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Old Jan 21, 2013, 02:53 AM   #3
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Originally Posted by Jarek104 View Post
Hello everyone. Yesterday me and my friend replaced the CPU (2.8 i5 with compatible 2.93 i7) in my mid 2010 iMac using this tutorial:http://www.hardmac.com/articles/335/page1 . Everything works fine. iStat reports cpu temp of 35, HD= 41, optical drive= 31 and ambient=16. optical drive fan is 1000rpm, HD fan is at 1200 rpm but for some reason the CPU fan shows 0rpm while working like crazy. I spent the whole day looking for the answer on different forums, reset the SMC and PRAM, took the iMac apart again to check all the connections and even took it to apple store. Unfortunately I was told that they won't help me since I upgraded the CPU. The hardware test they ran showed indeed 0rpm for CPU fan but that's all the info i got from them. I also read somewhere that I could install resistor to slow down the fan but I have no idea which resistor to use and on which wires it should be installed. ANY help would be appreciated.
No ESD protection while procedure I guess sorry mate you short the cpu thermal sensor which is on the motherboard that mean you have 2 solutions first order a new mobo and second to add a resistor to the fan.To add a resistor find in the 4 pin fan connector in mobo the pins that give the voltage with a multimeter there are two.Add the appropriate resistor to reduce the voltage from 11volt(fan full speed) to 5 volt so the fan be quiet.

Last edited by chevalier433; Jan 21, 2013 at 02:59 AM.
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Old Jan 21, 2013, 03:14 AM   #4
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Soldering ...

... a resitor between 80 to 120ohm to one of the cables of the CPU fan should make it silent enough, but giving the CPU the best possible cooling.

Another option might be that you detached one of the other fans of your iMac, and the CPU fan now is trying to compensate for the lost cooling - thatīs why it may show a wrong/no rpm count.

Last edited by giffut; Jan 21, 2013 at 03:23 AM.
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Old Jan 21, 2013, 03:40 AM   #5
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... a resitor between 80 to 120ohm to one of the cables of the CPU fan should make it silent enough, but giving the CPU the best possible cooling.

Another option might be that you detached one of the other fans of your iMac, and the CPU fan now is trying to compensate for the lost cooling - thatīs why it may show a wrong/no rpm count.
Wrong two wires give voltage.The last thing that you said is not possible istat and AHT show 0 rpm.
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Old Jan 21, 2013, 05:34 AM   #6
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Originally Posted by Jarek104 View Post
Hello everyone. Yesterday me and my friend replaced the CPU (2.8 i5 with compatible 2.93 i7) in my mid 2010 iMac using this tutorial:http://www.hardmac.com/articles/335/page1 . Everything works fine. iStat reports cpu temp of 35, HD= 41, optical drive= 31 and ambient=16. optical drive fan is 1000rpm, HD fan is at 1200 rpm but for some reason the CPU fan shows 0rpm while working like crazy. I spent the whole day looking for the answer on different forums, reset the SMC and PRAM, took the iMac apart again to check all the connections and even took it to apple store. Unfortunately I was told that they won't help me since I upgraded the CPU. The hardware test they ran showed indeed 0rpm for CPU fan but that's all the info i got from them. I also read somewhere that I could install resistor to slow down the fan but I have no idea which resistor to use and on which wires it should be installed. ANY help would be appreciated.
Why you did that?How stupid...people spent a fortune to buy a Mac and they destroy them
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Old Jan 21, 2013, 05:51 AM   #7
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OP, take it apart and check if LCD temp sensor is connected properly. If it isn't, or sensor cable or its socket is damaged, CPU fan will act exactly like this.
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Old Jan 21, 2013, 06:07 AM   #8
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Wow thank you for fast responses! Obviously I dont want to spend $500+ for something that could be "fixed" with few cents worth resistor. I'm going to order it online. My question is which one should i pick? 80-120ohm but how many watts? There are resistors available with anywhere from 0.25W to 20 and more.. I don't know much about that stuff. Also, since there are 2 "hot" wires, can interrupt any one of them? How much time does it take for a resistor to burn out? I know thats a lot of questions but now, when I learned how delicate those things are, I don't wanna mess anything up again.

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I did that only because i needed more power from my mac since some of the plugins I run in Logic were laughing at my i5

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Oh, thanks 666sheep. Will do it after!!
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Old Jan 21, 2013, 06:22 AM   #9
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*After work
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Old Jan 21, 2013, 07:08 AM   #10
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*After work
When i have time I will do a research to tell you the exact wires and the resistance you will need to run the fan at 1200 rpm.You can buy a external box,pass the cables out of the "cooling holes" bottom of the mac to adjust the fan speed manually.You can find at ebay logic boards at 300 dollars.
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Old Jan 21, 2013, 07:55 AM   #11
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That would be very helpful. I will take a look at those external boxes. Thank you for your time
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Old Jan 21, 2013, 01:58 PM   #12
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When i have time I will do a research to tell you the exact wires and the resistance you will need to run the fan at 1200 rpm.You can buy a external box,pass the cables out of the "cooling holes" bottom of the mac to adjust the fan speed manually.You can find at ebay logic boards at 300 dollars.
While researching about those resistor boxes i came across information that tahometer in the fan is used to send impulses to motherboard which based on the number of impulses determines the rpm of the fan. Is there a chance that that mechanism in the fan will not work, thus will not output impulses to the motherboard? If that would be the case, I would need to only replace the CPU fan. Correct?
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Old Jan 22, 2013, 03:27 AM   #13
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While researching about those resistor boxes i came across information that tahometer in the fan is used to send impulses to motherboard which based on the number of impulses determines the rpm of the fan. Is there a chance that that mechanism in the fan will not work, thus will not output impulses to the motherboard? If that would be the case, I would need to only replace the CPU fan. Correct?
Conversely motherboard fan circuit sent impulses to fan.I have seen this problem before its not the fan it's mobos fan circuit.Do you have any electronic knowledge or skills to tell you the procedure?

Last edited by chevalier433; Jan 22, 2013 at 03:33 AM.
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Old Jan 22, 2013, 04:57 AM   #14
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Conversely motherboard fan circuit sent impulses to fan.I have seen this problem before its not the fan it's mobos fan circuit.Do you have any electronic knowledge or skills to tell you the procedure?
Unfortunately I don't know anything about fan circuits but soldering is not a problem. I figured out which wire carries 12V. I'm going to get 100Ohm 5W resistor and will install it on that wire. Will let you guys know how it worked out when I'm done.
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Old Jan 22, 2013, 05:38 AM   #15
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Unfortunately I don't know anything about fan circuits but soldering is not a problem. I figured out which wire carries 12V. I'm going to get 100Ohm 5W resistor and will install it on that wire. Will let you guys know how it worked out when I'm done.
Soldering knowledge is enough 100ohm resistor is the one you need the wires are the first and the forth from the upper left.First is the voltage and the forth is the one that you previous mention in your post you need to both cut the wires and solder the resistors.
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Old Jan 22, 2013, 07:03 AM   #16
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Unfortunately I don't know anything about fan circuits but soldering is not a problem. I figured out which wire carries 12V. I'm going to get 100Ohm 5W resistor and will install it on that wire. Will let you guys know how it worked out when I'm done.
Before you'll solder anything, check what I said before. I think that's your issue. Read last two answers in this thread if you don't believe me
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Old Jan 22, 2013, 01:33 PM   #17
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Before you'll solder anything, check what I said before. I think that's your issue. Read last two answers in this thread if you don't believe me
The thing is that when I took my imac to the apple store and they ran the AHT the only problem it found was the cpu fan. I didnt receive any error code. They didnt want to help since I upgraded the CPU. What if i took it to different apple store and didnt tell them about the upgrade? Would they run the complete diagnostics? How should I check the connection with the sensor? And where can i check what temp that sensor reports?

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Quote:
Originally Posted by chevalier433 View Post
Soldering knowledge is enough 100ohm resistor is the one you need the wires are the first and the forth from the upper left.First is the voltage and the forth is the one that you previous mention in your post you need to both cut the wires and solder the resistors.
Can I please ask you about the reference for that information? I thought the 12V is all i need..
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Old Jan 22, 2013, 02:04 PM   #18
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The thing is that when I took my imac to the apple store and they ran the AHT the only problem it found was the cpu fan. I didnt receive any error code. They didnt want to help since I upgraded the CPU. What if i took it to different apple store and didnt tell them about the upgrade? Would they run the complete diagnostics? How should I check the connection with the sensor? And where can i check what temp that sensor reports?
To test it yourself without dismantling whole unit, you'd need ASD 3s140. To check connection and cable visually, you'd need to take iMac apart. As poster in previously linked thread said, it's easy to damage sensor cable while tightening screws:
Quote:
This cable runs very very close to one of the 4 long screws you have to remove to get the aluninium frame off, the sharp thread on the screw and cut one of the two temp sensor wires, you could barely see damage to the heat shrink
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Old Jan 23, 2013, 11:27 PM   #19
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To test it yourself without dismantling whole unit, you'd need ASD 3s140. To check connection and cable visually, you'd need to take iMac apart. As poster in previously linked thread said, it's easy to damage sensor cable while tightening screws:
Ok I ran both the EFI and OS tests. I had few errors..
OS:
-cpu fan motor is stalled (not sure what that means)
-HD fan unable to stabilize
-cpu fan unable to stabilize
EFI:
-HD fan is spinning too fast
-CPU fan is spinning too slow (it takes few seconds after I boot up but then it spins like hell)

All other hardware passed the test.

ps I know I should not even have the ASD, and I also understand that the apple technician didn't want to look inside my iMac, but I won't just leave it like that only because they don't want to help me..
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Old Jan 24, 2013, 02:02 AM   #20
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-cpu fan motor is stalled (not sure what that means)
I.e. fan does not spin. At least you iMac "thinks" that. Grab your tools and disassemble the thing. Or try another AASP if you're afraid to do it yourself.
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Old Jan 24, 2013, 07:33 AM   #21
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Ok I ran both the EFI and OS tests. I had few errors..
OS:
-cpu fan motor is stalled (not sure what that means)
-HD fan unable to stabilize
-cpu fan unable to stabilize
EFI:
-HD fan is spinning too fast
-CPU fan is spinning too slow (it takes few seconds after I boot up but then it spins like hell)

All other hardware passed the test.

ps I know I should not even have the ASD, and I also understand that the apple technician didn't want to look inside my iMac, but I won't just leave it like that only because they don't want to help me..
Dude...I told you whats wrong you short the fan circuit of the motherboard that why istat and test show fan speed 0 if any sensor broke or forgot to assemble the fan should be 2500 rpm and you would had a sensor error.I told you the solutions resistor in fan,used mobo from eBay or take the mobo to someone who can fix it.Even if apple technician open your iMac he will see that you remove the warranty void if remove stick from cpu heatsink.
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Old Jan 24, 2013, 11:02 AM   #22
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I.e. fan does not spin. At least you iMac "thinks" that. Grab your tools and disassemble the thing. Or try another AASP if you're afraid to do it yourself.
I installed smc fan control and it shows 0 temp for my internal hard drive..
As far as i know smc fan control uses the internal temp sensor while istat uses the external sensore of the HDD.
After reading post from lexvo on this thread http://forums.macrumors.com/showthread.php?t=1417443 i think im gonna order the hdd before trying jumping any sensor.
This would explain why it passed the ASD

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Dude...I told you whats wrong you short the fan circuit of the motherboard that why istat and test show fan speed 0 if any sensor broke or forgot to assemble the fan should be 2500 rpm and you would had a sensor error.I told you the solutions resistor in fan,used mobo from eBay or take the mobo to someone who can fix it.Even if apple technician open your iMac he will see that you remove the warranty void if remove stick from cpu heatsink.
If new hdd sensor won't help i will probably use the resistor

Last edited by Jarek104; Jan 24, 2013 at 11:08 AM.
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Old Feb 5, 2014, 01:22 PM   #23
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The thermal sensor used on the MacPro motherboards is a 2N3904 NPN Small Signal Transistor (http://www.radioshack.com/product/in...ductId=2062609). About a buck for a pack of three IIRC.

Check out "http://www.insanelymac.com/forum/topic/77290-building-a-macpro/page-17" for the directions.

Worked for me.
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