CPU fans on 2010 iMac 100% after SSD install

The mysterious fan spinning on most iMacs can be solved using a simple transistor. I just did it in a 27" iMac Mid 2010. The photos below hopefully will help others as I could not find any substantial explanations.

This model uses a Hard Drive with an additional 8 pin header along with the Sata and Power connectors on most HHD's.

There is an internal sensor built in these Hard Drives that does not exist on SSD's. A transistor can be used to satisfy the Logic boards need for a temp reading just like on the older models where it is attached to the body of the HDD as in the 2008 models.

Example of older hard Drive with sensor attached to body:

Use a 2N3904 transistor and bend the leads as in the photo with the flat side facing you.

Below is a transistor slipped into 8 Pin connector as in 2010 iMac with internal Hard Drive sensor using the :

You can also solder the transistor as shown below:

I

As far as I understand does Apple use a non-standard power connector which feeds temperature information from the SSD back to the logic board. You have this connector only when you buy the iMac with the SSD pre-installed.

If you install a SSD later on using a standard cable, the logic does not receive a temperature reading and assumes the senor in the SSD has failed. As a result it forces the fans to work a 100% to prevent overheating. So there is noting much you can do, unless you want to get your hands a bit dirty. See in that case: http://forums.macrumors.com/showthread.php?t=808178&

Hope it helps.

Did you ever find a resolution for this? I added an Intel SSD to my late 2007 iMac using the same tutorial and have the high CPU fan problem. It's spining at ~3900 rpm and SMC or PRAM reset or any of fan control utilites didn't help the issue.

Thanks.

I just upgraded my mid 2010 iMac 27 inch to an SSD which was installed at microcenter. After the upgrade my HDD/SSD fan goes over 4000 RPM and will not come down. It takes it about 10 minutes to get there after turning it on.

The sound is heard all around the computer, but I figured out it is coming out of the circular intake vent in the center back of the computer behind the arm stand.

I called microcenter general tech support number and they didn't know and I'm waiting to hear back from the service center at the store.

The HDD proximity temperture is always low at 48 Deg F. So there is no reason for it to be so high. The CPU and optical fans are not effected and both stay around 900 RPM.

I did some research and it looks like it might have been the sensor and the mounting kit they used to convert it from 3.5 to 2.5 size. Maybe the kit they used didn't have a place to connect the wire.

What do I do? Microcenter is an Apple certified service center so Apple should tell them how to do the service so this doesn't happen.

This software fix works for now (see youtube link), but I want it fixed in the hardware, otherwise it will be a problem in windows and also I want it done right since I paid money for a certified professional to do it.

http://www.youtube.com/watch?v=6rdFT5yVROI

You go into Automator ->Utilities -> Run Shell script and paste this: "/applications/smcfancontrol.app/Contents/resources/smc -k F1Mx -w 1770"

My issue (CPU fan running high) turned out to be bad LCP pannel temp sensor connection.

As for HDD/SDD fan, I'm note sure, but the temp sensor on HDD may not be connected properly, or connected to wrong pins (only 3 pair out of 4 are used).

If you had someone install it, having them fix it is probably the best option.

I just wanted to add to this post after spending weeks on forums and trying every trick in the book to stop excessive CPU and Optical fan speed after a SSD upgrade on an iMac (9,1).

I had come to the conclusion of a corrupt SMC and thought i was looking at a new mainboard.

Turns out that the CPU and Optical fans will spin faster if a LCD temp sensor is at fault. During my carefull SSD install i had pinched the LCD temp sensor cable that runs from the lower left of the mainboard past a fan and behind the LCD display. 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.

I had formatted twice, reset SMC and PRAM more times than i can imagine, removed bootcamp partition and spoken to 3 certified apple techs at 2 different stores.

Quick solder and some trusty electrical tape and my imac was back to normal fan speeds.

FIXED THE ISSUE.... This took a little time, but it was a simple fix. The LCD sensor that you have to disconnect from before removing the LCD was the issue. After receiving HIGH CPU fan speeds, I began looking at possible issues. First, I had [http://www.macupdate.com/app/mac/12381/temperature-monitor|Temperature Monitor] Installed. I had all my sensors including the ambient air sensor reading. After I upgraded my HD to a SSD I started getting HIGH CPU fan speeds, but the HD and DVD fan speeds were fine. I looked at my Temperature Monitor and I noticed i had several Temperature Monitors not reading including the ambient Air Temperature (bare with me, these are steps to troubleshoot). After reseting the SMC and PRAM, still nothing. I shut down and disassembled my IMAC again. This time after i removed the LCD, I looked at the LCD cable that you must disconnect when removing the LCD and BAM, I saw the issue. The wires that connect to the Motherboard from the LCD Sensor, inherently like to lay across the screw hole the Bezel attaches to. I have a couple of pinched marked that exposed the wires and when I tighten the bezel down, it shorted the wires and caused the issue. I cut small pieces of electrical tape and covered the bare spots. When I reassembled the IMAC, i made sure that all my BEZEL screw holes were completely clear of any wires. Once back together, I plugged in the IMAC, waited 5 Seconds and turned it on. All is well. I feel this a majority of everyones issues when they take apart their IMACS and put them back together. THe Fan Control SOftware is good, but this was my solution that worked. Hope this helps.

Yes and thanks for your advice.i fix it 🙂