Chosen Solution
Hello, I performed the Dual Hard Drive Kit upgrade as suggested in the guide at Installing iMac Intel 27" EMC 2429 Dual Drive Kit (HDD or SSD) I followed the steps precisely during the whole process. After the second drive (SSD) was installed, I booted up the iMac and heard loud fan noise after a few seconds. Both CPU and ODD fans are running at full speed. I have tried resetting SMC/PRAM, but to no avail. I reassembled the logic board twice, with and without the Dual Drive Kit upgrade. It still didn’t fix the problem. So, I believe something somewhere has gone wrong and I need to identify the problem and fix it. I have also noticed that it is not just the fans that are loud, my game which I play every day at 30fps, is crawling at 6-7fps after the upgrade (still utilizing the HDD though, not the SSD). Running the Apple Hardware Test revealed failure with TA0P code, which indicates Ambient Temperature sensor/connector failure according to some google search results. Moreover, Temperature Gauge Pro app reports the following: ODD 3729 RPM HDD 1097 RPM CPU 3917 RPM Fan Diagnostics: These fans appear to be not working properly : ODD Sensor Diagnostics: These sensors appear to be not working properly : CPU Some further Googling has revealed that this person had a similar problem and flipping the LCD Thermal Sensor Cable fixed it for him: http://forums.macrumors.com/showpost.php… However, I’m not sure which of the cables mentioned in the iFixit guide are the LCD Thermal Sensor Cable, for me to give it a go (I doubt any of the cables can be flipped on this model though). Any help would be appreciated. TLDR: After installing 2nd drive (SSD) on 2011 27’’ iMac,CPU and ODD fans are running at full speed, HDD fan at normal.Degraded gaming performance at 6-7fps.Failure in Apple Hardware Test with code TA0p.Something somewhere went wrong in assembling/disassembling (perhaps). Thanks! Update (02/25/2014) I removed the LCD panel from the iMac and booted it with external Cinema Display. The fans are still loud. So I doubt that the problem is with LCD sensor. Maybe I should pay attention to the Ambient Sensor/connector, since the AHT failure also reported a fault with that.
I had this issue recently and after analyzing the schematics for the iMac 2011, I found that two tiny inductors (ferrite beads) in the ambient temperature sensors’ path have been knocked off somehow and that caused the ambient temperature sensor not to work and in turn the system sped the fans up and slowed the cpu down. This issue has nothing to do with the hard drive it just happens to many people while they’re disassembling the machine, the two inductors are right near the ambient temperature sensor connector (L5500 & L5501) and I guess can be knocked off easily. It can be fixed with some soldering skills and there’s no need to remove the logic board for the repair. I don’t think there is a need to replace the parts they’re just there to reduce some radio frequency. If you do want to replace them they’re both a 220 ohm ferrite bead SMT size 0402 (1005 metric). After my discovery I found some guys on a repair website mentioning a few times that they’ve dealt with this issue on the iMac 2011. That fix that was mentioned about the LCD temp sensor being inserted incorrectly was only for the iMac 2010 based on what I found in the schematic for that machine. This is a picture of my repair, I just added two traces of solder to replace the missing ferrite beads.
This issue, caused by Apples greed in putting proprietary drives in, can be solved easily by using this: OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade http://eshop.macsales.com/item/Other%20W…
Check the LCD Thermal Sensor Cable (vertical sync cable) and the cable to your main hard drive. You didn’t mention if you also changed the main hard drive or not.
I had an interesting endeavor with a Mid 2011 iMac 27”. I wanted to replace the broken harddrive with a new 2,5” one and add an SSD on top of it. I got the cable for the second drive and was able get everything up and running - except that the fans were running at full speed shortly after switching the iMac on. The first thing I came across was the issue with the non-standard HDD temperature reporting. I stumbled upon https://www.elvikom.pl/imac-21-5-27-blad… which describes that you can shorten two pins on the harddrive to let the iMac think temperature is normal. I did this on a Sabrent converter frame (3,5” to 2,5”) to avoid soldering directly on the harddrive. Guess what? Fans still spinning at full speed. Then I tried the OWC OWCDIDIMacHDD11 which is similar to the solution offered by iFixit to add an external temperature sensor for the HDD. Aaaand it was still not working. Fans at full speed. I was a bit out of ideas. Some weeks later I gave it another try. The whole time I was running the iMac with the display removed to make things easier while in repair. I had it connected to an external display. I ran the Apple Hardware Test and it showed me this error: 4SNS/1/C0000008: TL0P—124. I found out that this is a problem with the display temperature sensors. And indeed they were not shown by Macs Fan Control. Obviously, this was due to the fact that I didn’t have the display attached, However, even after attaching it I got the same error and fans spinning at full speed. I removed the display again and found the temperature sensor on its backside. I removed its connectors and re-attached them. Then I attached the display again and tried starting the iMac without the additional OWC cable (i.e., only with the soldering solution). And it worked! Fans were quiet and I could see the display temperature sensors being shown by Macs Fan Control. In the end, it seemed to be a problem with connectors of the display temperature sensor. So the iMac didn’t recognize them and turned on the fans. What a ride.
